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Sunday, September 11, 2011

Mending a pair of M-AUDIO BX5a monitors

One of my sons friends asked me if I could take a look at his speakers which had stopped working. he and my son had been mixing some songs using a pair of M-AUDIO BX5a monitors. These are bi-amped active speakers, with Pro audio style inputs (XLR and 1/4" mono jack). They each have two integral amplifiers so only need a line or balanced input. Each speaker also has a mains power input and a volume control, and a blue LED on the front to indicate power. The speakers have two drivers, a small domed tweeter and a small 5" Kevlar woofer. One had developed a loud buzz, coupled with a very loud 'thump' sound when powered off. The other had completely lost all bass output.The speakers were only 13 months old, which seemed a very short life for a pair of speakers - I have speakers made in the 60's that are still going strong. However with additional electronics in these BX5a's I'm not really comparing like with like.These speakers are self contained audio systems. All you'd need is a source like an iPod or CD player and you'd have a pretty decent stereo system. They are primarily aimed at pro audio monitoring use and retail for around £200. They are also very well reviewed on the web. I was also intrigued by the name. My own main speakers are a pair of Goodmans BBC LS3/5a speakers - something of a legend among small monitors. I thought the naming of the BX5a was perhaps a nod to these classics.

My first advice was to see if the shop he bought them from would be prepared to fix them as they were not that old. They would only fix for free when the speakers were within warranty, which these were not. Oh well ....I googled the speakers and some of the symptoms and pretty soon found dozens of hits on the buzzing problem, with the loud thump on power off . Again and again people 's BX5a had developed loud buzzes through both tweeter and woofer. It seemed that the speakers had fallen victim to a more widespread problem of poor quality capacitors. This problem has been the scourge of the IT Industry too, I have had a Dell Optiplex fail the same way. I understand that Apple Time machines have had problems with caps leaking/exploding too. Possibly it's due to the caps being a faulty batch or the temperature upper limit being exceeded and prematurely ageing them.

The power supply in the speakers uses a couple of 6800uF 25v caps to smooth the output from the 4 diodes making up the bridge. NOTE : the switched mode supply, ubiquitous in every other aspect would be too electrically noisy for these applications. Here we have good old linear supplies with diodes, and smoothing caps.These two caps appear to have a common problem where they leak. The top of the cap appearing to bulge, and in some cases electrolyte oozing out. These symptoms certainly seemed like one of these speakers , so I offered to replace the caps . I figured it was within my capability.

I should state at this point, that this is quite a hard repair to carry out. Some forums imply this is easy, but it took me around 90 minutes to do the first speaker, and 60 to do the second. You have to substantially dismantle the speaker and remove two caps which are soldered and glued in position. There are a lot of steps along the way.

I looked on-line at caps and in the end RS Components did suitable caps 6800uF 25v . In addition other important values are temperature (105 degrees) diameter (18mm) and lead pitch (gap between the leads - 7.5mm). The Cap length is not so important but you need to get all the other parameters the same. RS and Farnell have thousands of caps, but by the time you specify all these constraints, you are down to one or two , I went for these Nichicon caps. RS states that the caps come in packs of 2 , so I ordered a total quantity of 2, assuming this would equate to 2 packs of 2, meaning 4 caps. I had decided that while the second speakers problem was different, it was worth replacing the smoothing caps in both. It might fix the other problem, and I reasoned that it looked like this might become a problem in the second speaker at some point anyway. The package arrived 2 days later but only included 2 caps. I think I had been confused by the quantity &  the fact that 2 came in a single packet. Anyway I ordered a second batch and set to work on the speaker with the buzz. When dismantling these speakers you will need :

  1. a tray to keep all the screws in
  2. a medium sized Philips screw driver
  3. a No. 3 metric Allen key

I put a towel down on the table and laid the speakers face down. The front does not have a protective grille, but the drivers are recessed enough into the bezel that they don't protrude and laying them on their front is fine . 10 Philips screws hold the back panel in place and I carefully removed these, cupping my spare hand around the Philips screw driver point, so as not to slip and scratch the cabinets. This is more important later when removing the bass driver. It's very easy to stick a screw driver through a speaker cone if you are not careful - I have done this before and it's easy to avoid with care. Once all the screws were removed, the back is loose, but I soon realised that the cables inside connecting with the drivers on the front , were too short for me to gain access to the amp Cables ties had been used to gather up any slack, so I couldn't get the back panels with attached amps clear via the back.

I turned the speaker over, laying it carefully on it's back. the towel is important as the volume knob on the back protrudes, so laying the speaker on something a bit soft will save your tabletop and the speaker volume pot. The front bezel is held on with  No. 3 Allen key headed screws. At first this seems frustrating but actually is a smart idea. It means you can apply pressure in a plane across the speakers, not toward them (as with conventional screws). I still cupped one hand over each driver, while removing the Allen screws with the key in the other hand.

Once they are removed you can lift the bezel. The bass drivers are not attached to it, they are still screwed to the front of the cabinet. However the tweeter is attached to the bezel. You will need to disconnect the speaker wires from the tweeter to free it. The wires are coloured black and white and have identical sized pushed connectors. I photographed the tweeter at this point so I'd remember the tweeter polarity.

You can pull the speaker wires from the tweeter but take note of the polarity or better still take a picture. Once the tweeter is disconnected you can take the bezel and tweeter and place safely to one side. You then need to remove the woofer. This is held to the speaker cabinet by 4 Philips screws. Again, cup one hand over the driver while you carefully remove the 4 screws. It' very easy to slip and pierce the driver with a screw driver - I know, I have done it before, and kicked myself for my stupidity.

Once you remove the bass driver you do not need to take note of the polarity as the push connectors are a different size for positive and negative. Note the silver wires behind the tags - their significance is important - read on.

Once you have disconnected the woofer, place it safely to one side.

You will find you still cannot remove the backplate as the LED which indicates power is fastened to the front of the speaker. The cable slack has been wound with the excess speaker cable using a cable tie. I carefully cut the cable tie, releasing enough slack cable to allow the amplifier module to be removed from the speaker while leaving the BLUE LED cable in place.

Once the amplifier module was out I could see that the smoothing caps were failing as predicted.

You can clearly see the electrolyte oozing out of one of the smoothing caps and that the top of the cap is curved outward. Something inside is trying to get out !

To replace the caps you will need a de-solder pump or de-solder wick, a soldering iron and a craft knife.

However before you can gain access to the back of the board there is a metal plate which has to be removed. You can see the plate in the picture below. It's held on by a couple of screws on the right hand side, which also hold two earthing wires in place. These screws have been secured with green enamel paint or possibly nail varnish, which I had to chip away to access the screw heads. On the left a cable tie through a hole secures the plate.

I removed the screws on the right hand side and cut the cable tie on the left. The plate is further secured to the back of the circuit board with an adhesive strip. With gentle pressure the plate slowly came away. This gave me access to the back of the capacitors. I took a picture to remind me of the polarity of the cap leads (negative -ve and positive +ve). You can see below how bad one of the caps appears. The sticky electrolyte has got some of the speaker acrylic wool stuck to it, making it appear hairy !I heated the solder pads on the reverse side of the board where the capacitor leads passed through. I used the solder sucker to remove as much solder as possible. I then carefully cut with the sharp craft knife around the base of each cap to cut through the glue which has been used to further secure the cap to the board. This is a slow and delicate operation, hence my comment earlier about this being a difficult fix. You don't want to damage the surrounding components nor flex the board. It's possible to raise the copper tracks from the board if you apply excessive heat or try removing the solder too many times.

I did more de-soldering until I could bend the remaining length of lead up, allowing the cap to be slid out from beneath . Eventually each capacitor slowly loosened and I could gently pull them away. I further de-soldered the remaining holes and trimmed as much yellow glue from where the caps had been. It was then a case of inserting the new caps, checking the leads were correct. (Negative lead has a white strip down that side of the can ), re-soldering them and cutting the spare from the protruding leads.

If you chose the right value of capacitor ( 6800uF, 25v, 105 degrees, 7.5mm lead pitch, 18mm diameter) you should find that they fit perfectly, though might be a little taller, but there is plenty of space.

Once fitted I carefully reversed the process, fitting the plate back and applying a new cable tie through the corner hole. Fitted the rear panel in the box and then the bass speaker, finally the bezel. Always remember to use one hand to protect the drivers - that treble unit has a strong magnet in it and a wandering screw driver can easily be attracted to the soft dome if you are not careful.

I repeated this entire sequence on the second speaker, thinking that it a) might solve the other problem (loss of bass) and b) is probably a good thing to do. While the capacitors were not in as bad condition, there was a distinct 'doming' of the ends. I also checked the continuity of the two fuses on the amplifier board. Both were fine.

Powering up each speaker revealed no buzzing, the LED still came on and no big 'thump' noise on power off. Placing my ear next to each driver revealed a small amount of background hiss from each treble unit and a tiny amount of background hum from the bass, but this seemed normal to me. Unfortunately I have no interconnect cables to test the speakers with to hand, so returned them to there owner with the advice that he try them ASAP.

Well the good news was that the speaker that had buzzed, now worked perfectly. However the speaker that had no bass .............still had no bass.

I realised at this point that I had omitted to do the single simple test which would have saved me the following rework . I should have tested to bass speakers continuity while I had the driver out i.e tested that there was a circuit between the positive and negative terminals on the back of the disconnected speaker. An open circuit /no circuit would have indicated the speaker had failed internally, as it now appeared it had. Of course it could be other problems with the power amplifier ?

The offending speaker was returned to me. I had also found a cable I could use to test with an RCA plug on one end, and a 1/4" stereo jack at the other. The BX5a needs a mono 1/4" jack , but I knew it should work if I slightly remove the jack so that the internal contact touched either the left of right band on the jack. This was a mono cable, so both were wired to the signal in a single RCA.

I repeated the steps above as far as removing the bass driver, and tested it for continuity. No circuit ! This was good in so far that had the driver blown completely it was a relatively easy procedure to order and drop in a new driver.

I wanted to double check the speaker was not functional , so wired it up to one channel of a small desktop Sonic Impact T-amp I had. I turned the volume to quite low and played some music. Without a cross-over the sound would be bass heavy, but I figured it should produce some sound.

Nothing, as the continuity test had predicted.

I sat down and started web surfing to see get a cost for a replacement bass driver. The M-AUDIO website was not very helpful here. I could find no links for spare parts.

I stared at the driver and , without much thought double checked the continuity again. My trusty TANDY/Radio Shack digital meter has a simple beep continuity mode, where it beeps if it sees a circuit. I tried the positive and negative terminals again. No change.

Then I tried the wires that lead to the terminals from the centre of the speaker voice coils - short lengths of silver wire.

BINGO ! We had continuity.

Further tests showed that the negative terminal of the bass speaker was open circuit. It looked OK, but it appeared that the solder joint was not good. I de-soldered it and resoldered it, and the speaker was fine. I put the second speaker back, after testing it quickly outside the cabinet with my CD player (A Sony Playstation 1), my RCA to stereo 1/4" jack plug and a much loved copy of "The Kinks are the Village Green Preservation Society".

Worked fine so put the speaker back together again. Job done.

A final puzzle: "phased and confused"

It's impossible to connect the bass drivers incorrectly as the spade connectors are different sizes for positive and negative, red and black. However the connectors on the tweeter are the same size.

I noticed that the tweeter connections are mirrored. Rather than both tweeters being connected the same way (black left , white right connector), the arrangement is inverted in the second speaker. I'm not sure about this. I don't know too much about this tweeter but would assume, that like the bass driver, both speakers should be wired identically to preserve absolute phase ?

Here is one speaker, with the bezel disconnected, photographed from the top:

Here is the other speaker, with the bezel disconnected, photographed again from the top:

I guess if the treble sounds a bit odd, you might want to check if your treble units are wired in phase or out of phase with each other ? I think they should both be in phase, both with each other and with the bass drivers, though how you tell is unclear as neither tweeter connection tabs were labelled.


Postscript: revisited 19/4/2012

My sons friend contacted me to say that one of the speakers had lost its bass output, and he thought it was the one that originally had the hum problem i.e not the one that previously needed the bass tag resoldering.

He dropped the speaker off, we followed the dismantle sequence above, I removed the bass driver and put a multimeter in continuity mode across the two tag terminals on the speaker. Sure enough - nothing. I then repeated this but gently putting the probes on the silver wires behind the tabs. Once again i had continuity i.e measurable low resistance, not open circuit. By trying the four combinations of two probes on two terminals and two wires , I figured out it was the right had tab looking at the speaker with the woofer facing upward.

Pleased it was a problem we had encountered before i used a solder sucker to remove the solder around the connector, then resoldered it. I put the speaker back together and played some music, all seemed well as "Picture book" by The Kinks played out. A great track and as i had the mono recording it gave me a familiar sound through only one speaker. Pleased with our results , my son suggested something louder and so "Achilles Last Stand" by Led Zeppelin, which is in stereo so we'd only get one channel, but still good. I mention this because half way through we lost all bass. The problem had returned !

Repeated the process, but this time spent longer using the solder sucker . When the connector tag was as clean as i could get it and i could see the hole through it, this time I poked the silver wire from the voice coil through the hole from back to front and gently bent it over. Don't pull it too far through, otherwise you could damage the driver. Just a mm or so, then held it with tweezers and made a good solid solder joint.

Repeated the Zeptest and it survived all of Bonhams drum fills, and is working  and back with its owner.

....So it looks like some bass speakers, certainly the ones in this pair, suffer from a poor solder joint , in both cases on the black wires terminal, where the voice coil wires connect to the push on connector terminals. A good re-solder seems to fix it.

I have since been advised that this is a stress fracture. The braided wire which liks the coil to the tabs has to flex. If soldered badly the solder creeps along part of the braid making it stiff. At this juncture between solder and non-solder braid, you get stress ractures. A tip which I will try next time is to de-solder the braid completely and apply some super glue close to the end where the-joint will be . This will prevent solder from creeping along its length by capillary action when molten.

Another BX5a and a BX5 (update 16/9/2012)

My Son wants to get a pair of BX5a and I was on the lookout on ebay for any examples for spares or repairs, reasoning that I could get them working , and that even a new pair might need the above fix anyway over time.

Not many are listed for spares or repair but eventually a single BX5a came up and the seller also listed a single BX5, its earlier precursor. The seller had sold the working second speaker of each type to a friend.  We hatched a deal where if I could get both broken examples working , we'd swap and I'd get the BX5a's and the friend would have the working BX5. What could possibly go wrong ?

 I should add that the seller was completely honest about the speakers, describing the BX5a as having the hum and thump problem as above. However the BX5 had a "static" sound. I wasn't sure but thought it worth a go.

The BX5a responded to exactly the process described above. The bezel was slightly different . As before the main problem is getting the caps off the board, where careful , firm pressure is needed with a craft knife.

The BX5 is a completely different beast. Different drivers, bezel, and different inards. Actually marginally easier to work on as each drivers cables attach to the motherboard with push connectors, as does the LED. The problem was, as described. When I turned on the speaker with no connected source, there was a loud rustling through the bass driver, rather like someone rubbing a Microphone. This was independent of volume settings. The BX5 also has a number of EQ settings and these too made no difference. The Caps looked OK, no leakage or signs of stress.

To be honest at this point I was out of my depth with the BX5. I asked a local repair guy who I have used before to have a look at it. He concluded that the chip amp was the source of the problem, but having de-soldered it and re-soldered it once, he was very dubious he'd be able to complete the maneuver a second time with a new amp. The boards are not made to be fixed.

So, I have a working BX5a and a non-working BX5. A gentleman at the other end of the country has a working BX5a and a working BX5.

If anyone (ideally UK based) has either :

1) a BX5a with the hum & thump problem they want to sell


2) has a single working BX5 they want to sell

 please contact me.

Alternatively if anyone wants a BX5 for parts ( drivers, cabinet, bezel), also please contact me through the comments section

Postscript February 2013

Well my son needed a pair of active monitors for his college work on music production, and I'd only managed to source one fixable BX5a from ebay see above). hence I faced the need to buy a pair of BX5a or similar. In the end I opted for a pair of Fostex 0.4 monitors, similar to the BX5a in terms of features. They are a little smaller. he seems pleased with them. Why didn't I opt for the BX5a ? Well the story above shows that while they have a good sound, I think their build quality could be better.

September 2013 - More pictures

I had  a comment on the Blog from Joey McGowan asking about the wiring from the transformer. I hadn't taken pictures of this area, so opened up my one remaining fixed BX5a and took a few more. Its quite densley packed in the area of the transformer, AC selector, rocker switch and AC socket, there are also shink wrap "boots" over the backs of the AC socket, switch and AC voltage selector, with cables ties. I left these on as I don't really want to have to replace.

I took these notes which I *think* are right (please double check) and I hope are useful combined with the pictures below . Please double check and remember that these are correct for my unit, but colours may change. Anyway here goes:

Transformer (TX)

White -> Rocker switch
Red -> AC voltage selector
Yellow -> AC selector
Green -> AC selector
Dark Blue -> Mains IEC socket

Rocker switch

White -> TX
Red (Fat, different wire than from TX) -> Mains socket

Mains socket
Yellow + Green combined  Earth -> Screw on Sheild and Heat sink
Dark Blue (Fat , different from TX) -> AC selector
Dark Blue -> TX
Red (FAT) -> Rocker switch


Anonymous said...

Thank you for taking the time to post this. I have the same problem with 1 of my BX5a's but was unsure on how to disassemble it. This will serve me as a great example and a helpful guide. Once again you have my thanX!

Mr Ives said...

My pleasure. It's quite a fiddly repair, but if you take your time and are careful, it's well worth it. Getting the old cap off the board is the hardest part, but just take it slowly, de-solder as much as you can and gentle prise the cap off while applying some heat to the 2 cap leads.

best of luck

John Mannion said...

Thanks for a memorable post - took me longer to read than it did to resolve my last major speaker issue - when they failed to do justice to the Clash's 'I Fought the Law' they were dispatched single handedly to the bin whilst I did justice to another Boddington's with the spare hand!

Mr Ives said...

Well John, a typical punk response, if I may say so. Should have listened to the Kinks as I did, while drinking some Fullers.


`NiCK^ said...

I've been searching far and long for this. At least now I know how the insides of my speakers look like! Thank you.

One tip about desoldering, if there are delicate tracks on the board around where the caps are, a solder wick would be great for desoldering as you won't shock the board as much as a solder sucker.

Quick question, I sometimes have some music playing in the background while I sleep, and blue LEDs are not really the easiest on the eyes and am interested in swapping them out for dimmer white ones.
I can see spade connectors to the board for the LEDs, but how is it connected on the other end, will I need a glue gun to mount the LEDs back in place?

Thanks again.

Mr Ives said...

My pleasure Nick, and thank you for the tip about using solder wick rather than a solder sucker.

On the example I worked on the Blue LED's appeared to be hot glued into the front baffle of the box. Some posts I read implied that in some cases the LED is just a push fit.

I wonder if an alternative might be to use a resistor at the circuit board end to dim the LED , guessing something like a 300 Ohm ?

You'd need to remove the spade connector and solder the resistor in series, but might be easier than trying to get the LED out if glued ? Just a thought

Anonymous said...

I'm a university student studying sound engineering. This was my first university project, and it worked very well.
You have nice hands.

Mr Ives said...

Anonymous. - thanks, but clearly you have never seen my hands

Howard Long said...

For info I had the same buzz problem on one of my BX5a's. Sorry I didn't see you post before! However I managed to fix it in about 30 mins without even resorting to the Internet - the buzzing symptom and the oozing cap were enough, although mine just had a film yellow/orange gunge, not the mould. I had some 2200uF 63v in stock and used that and it works fine.

I suspect the original 25v caps are rather underrated for voltage purposes. 35v would be better. I measured pretty much 25v on them: too close for comfort IMHO.As you say there's plenty of space for a slightly larger radial cap with 7.5 mm wire ends.

Cheers, Howard

Mr Ives said...

Thanks Howard,wise words re. Choosing a higher voltage.

Out of interest have you solved the puzzle of the tweeter polarity ? The examples i had were wired as a mirror pair. I have since learned how to check the polarity of a mid or bass with a 1.5v battery, but thats not going to help with that tweeter.

El Complicado said...

Hello, I think my left speaker has developed the same issue and I was wondering if you would repair them (obviously for a fee) as I am less experienced with soldering new parts.
If I sent them to you (as you're in the UK) would this be possible. If not, I will try it myself, but I'm just wary.

Mr Ives said...

Greetings El Complicado

Sorry to hear your speaker has developed similar symptoms. I'm just an amateur and not a repair shop, I've also a stack of other repair jobs to get done when I get a chance. Where are you located and what are the symptoms ? The buzz and thump at switch off is the cap replacement and is the harder problem to fix. The loss of bass is simply a bad joint and quite easy to fix ? I would have though a local electronics repair shop (i.e Audio or TV repair person ) would be able to fix the cap problem. Most charge Time & Labour plus parts.

Tim Butler said...

Your detailed description of the disassembly gave me courage to attempt my own power filter capacitor replacement. I had the same problem (thump on power on and hum). My initial inspection of the speaker didn't seem to match others' descriptions. My speaker's construction is the same as yours with glued components and the grounding metal plate adhered to the bottom of the board. I assumed the glue would prevent a component replacement. One of my capacitors was glued to an adjacent smaller cap, but patient cutting with an xacto kife worked. It was encouraging to know somebody had already blazed the way.

It helped to realize I would not have to disconnect the LED to make the repair. I used Nichicon 6800UF 25 V capacitors from digikey: These were the same diameter as the originals, although much taller. Fortunately my configuration had no problems with clearance.

This was the first repair like this that I have made.

Some other hints: I was able to push the front bezel out from the rear port. Only the 10 outer screws on the rear need to be removed. I used tweezers, wick and a flux pen to remove the solder.

BTW - my tweeters were wired in phase.

Mr Ives said...

Thanks for the comment Tim, glad it worked. Also thanks for confirming your tweeter polarity. Which of the two pictures represents the way your tweeters were wired ?

Tim Butler said...

My tweeters were wired with the white wire on the right (looking down from the top) connected to a terminal that was colored purple.
This would correspond to your second photo.

Anonymous said...

power switch on back easy or hard to move it to front?i dont like it in the back

Mr Ives said...

very hard I would say . There is little space at the front of the speaker. You would need to run mains cabling from back to front, which I think would be hard and possibly dangerous. perhaps using something like this would be easier :

Anonymous said...

I have a pair of BX5s, one of the speakers stopped working yesterday. No hum, no hiss no thumps, it's dead silent. The LED is still on though. Was your LED on when the capacitors were failing? I will open it today and check for electrolyte leaks and such. Just curious about the LED.

Mr Ives said...

Hi Anonymous, both times when I saw failing caps, the LED was still shining.

There are a couple of fuses on the amp board and it could be that one of these has blown. While a failing cap could cause total failure, I'd expect it to take a while and pass through the loud hum phase first. Check all your internal fuses first

Anonymous said...

Thank you Mr Ives! I checked the fuses, both visually and with the multimeter and they appear ok. As far s the caps - there is no visible leak but one of them looks bulged. The top is not cracked, just a little "bumpy". The other one is flat on the top and has a QC sticker. I also conducted a simple test with the capacitors and something seems flaky here. I used 1.2V battery to charge the caps and then measured the voltage. The cap with the flat top worked as expected. First showed 1.1V or so and then the voltage started dropping slowly as I was looking at multimeter. The other cap always shows 0.08V and it does not charge nor discharge, even if I short the leads.

Mr Ives said...

Hi Anonymous, Hmm interesting. Does sound like a busted cap, its just Id expect the amps to "soldier-on" , even with a half smoothed supply (hence the hum). Having removed them for testing I guess you have little to loose in replacing them, I have my fingers crossed

Chris (anonymous dude from previous posts) said...

You were right. I replaced the caps (confirmed they were busted) but all I get now is loud click about 10 seconds after I power on. At this point I'm considering replacing the entire internal amp with something like this:
The drivers are ok, the transformer works, so why waste it :)

Anonymous said...

Your description "with Pro audio style inputs (XLR and 1/4" mono jack)" isn't quite correct. TRS is Tip Ring Sleeve and is a 3 pole connector - mono jack is just tip and sleeve and therefore 2 pole.

Anonymous said...

Tried this fix... now my BX5a wont turn on at all. Any suggestions? Thanks!

Mr Ives said...

Sorry your speaker won't turn on. You need to retrace each step, which means dismantling the speaker again. I assume you had the same initial symptoms i.e loud hum through the speaker and a big thump noise when turned on ?

1) Are all fuses back in place . It's not necessary to remove them, but worth checking and worth checking continuity across each fuse

2) Were all wires put back in place ?

3) You managed to remove the two old previous caps. Did you put the new ones in the correct way round (polarity)and were they the correct value. Are the solder joints good .

4) I assume you tested the speaker with an input and its not just that the blue LED has become disconnected ? This is very easy to do, but the speaker should still work fine.

As I said, its quite a hard fix, but if you truly have no power and the speaker is making no noise, then I would suspect one of the above

Jameson said...

Great post!

One of my BX5as sounded like it was clipping on loud bass transients, there was a slight buzz, and it was popping when being turned on or off, so I suspected that the power capacitors were the problem.

I replaced them with 6800uF 25V Nichicon KA series capacitors (link); KA is a new series that is supposedly designed for audio. They worked! No more buzz or clipping.

However, the speaker's volume seems to be significantly lower than it was before. The other speaker sounds louder and the repaired speaker sounds a little bass-light. The woofer is working and both drivers sound in phase. The bass-lightness could just be my imagination because lower volume gives the impression of rolled-off bass. Either way, it seems odd that new capacitors with the same specs would cause a noticeable volume drop. Maybe I will report back when the other speaker has had the caps swapped as well. My solution for now is to turn up the input knob on the repaired speaker. The resulting sound is pretty good, so maybe it is something inherent in the parts difference.

Jameson said...

I should also add that in my case the capacitors in the problem speaker were not bulging or leaking. They looked normal. However, replacing them still fixed the major issues. Appearances can be deceiving!

Mr Ives said...

Hi jameson, Interesting.
While I'm aware of audiophile caps, they typically have a better high frequency response. An old trick used to be to put a small value PP cap across a PSU cap to provide better response at higher frequnecies.

The Bass driver would be hard to install out of phase as the + and - connectors are different. The tweeter is harder to predict but lets assume you put it back as you found it.

Assuming you have some bass , perhaps the other speaker which sounds louder is in fact clipping also ?

I think I'd tryy listening to the repaired speaker on its own with a known Mono source. I love the Kinks and have some of their recordings in Mono. Then repeat for the other speaker.

It could be that repairing the other speaker might balance them (probably a good idea as it will probably fail at the worst possible time). The only other thing I thought was if the volume pot at the back had been damaged when laying the speaker down ?

Sometimes these things can be very subjective and its easy to convince myself of some change in the sound. I think the Mono test might be a good way forward

martianka said...

Hi I have a pair on 1 bass speaker not working,took speaker out and tried an old vox bass speaker no joy,so it,s tha amp I guess.i,m no electrician (no surprise!) any easy remedy to start with?? thanx nick

Mr Ives said...

Hi Martianka,

Hmmm, well I never had exactly that experience. I think I'd want to double check the MA bass speaker just to be sure (I've had 2 with the bad joint problem). Don't know if you have any means of trying the bass speaker. You could potentially wire it across an amps + & - connections on one channel. Turn the volume right down first, then apply some volume. may sound a bit "thick" but it should confim th driver is OK.

I think you have to trace your steps back, but there are two fuses on the motherboard, I assume one for the high freq amp and one for the low freq. It might be that one has gone. Easy to check, if you pop each out, either test with a multimeter (continuity mode or simply test the resistance) or you might be able to check by sight i.e see if the wire has a break, the fuses are a tiny glass tube.

If the fuses is OK and the driver is OK, then we are into unknown territory. Given the dry joint problems with the bass speaker, I'd test the continuity between the two bass wires and the amp board, just in case one is bad at the other end.

If its still dead, I think you are entering the realms that only a repair shop could fix. While I like these speakers, and was pleased to get a few pairs working again, I don't think they are that well made. I got my Son Fostex PM0.4 which perform a similar function and so far have not died.

Paulrus said...

I realize your original post is quite old, but thank you for posting it!

I have the same speakers and they died just after the warranty had expired. I too contacted the reseller as well as the manufacturer and neither of them were helpful at all. I will NEVER buy their products again after how they handled the situation.

The speakers have sat in a corner since then and haven't been touched. Today I was cleaning out my office and thought about tossing them out. But then I came across your article & now I think I might try to fix them.

Thanks for the great article!

Mr Ives said...

Thanks Paulrus for your kind words.

Well if your speakers died in the same manner i.e loud hum and a thump when you turn off, its almost certainly the same problem. Also if you inspect the caps on the board and they are domed at the end or bulging, then its probably this problem too.

What symptoms do your BX5a's have ? I have not managed to fix issues other than 1) the leaking caps problem and 2) The bass units dry joint/stress fracture problem as detailed above

Ed Glazer said...

Hey Mr. Ives, just wanted to say thanks for posting such amazing detail on this common problem. Had been getting the "thump" on power on/off for a while, but thought it was something related to my soundcard setup. Now that i've got "the buzz" I'm betting that cracking open the BX5a will show some busted caps. Thanks for the walkthrough, and for continued troubleshooting, it's greatly appreciated!

Mr Ives said...

Hi Ed and thanks for the kind words. Good luck with the fix. Its a bit long and fiddly, but if you take your time and are careful, especially when removing the drivers and also trying to get the old caps off, you should be fine. The speakers that have been fixed have stayed fixed BTW

Space Jogger said...

I really appreciate your post. I just made this repair and my speaker works again! Thank you!!!

Mr Ives said...

Thanks Space Jogger for the feedback, glad you're up and running again

Mark4931 said...

Are there a total of two identical caps in each cabinet? If I wanted to replace all the caps in my set, I would need four in total, correct?

Mr Ives said...

Hi Mark4931,

yes you are correct, there are two identical caps in each speaker so you need 4 to replace the caps in a pair of BX5a. I think it is worth changing all 4, and probably easier to do at a single go , having done one , the second one afterwards will be easier than having to get everything out at a later date. I mentioned in the thread that I was confused by the component suppliers web site as it implied that the caps came as 2 in a pack, so order quantity of 2 implied to me that I'd get 4, whereas it mean precisely 2 irrespective of how they are packaged. Good luck with your repair.

Joey McGowan said...

Hi Mr Ives

I came across this post as I have an M-Audio monitor that i'm trying to repair. The transformer is gone I got a new one but the wiring is colour coded differently. I wonder would have a picture of the wiring coming off the back of the AC select and power switch? So I can match up the wires. Regards Joe

Mr Ives said...

Hi Joey, the only pictures I have are the ones on the site BUT I do have one repaired BX5a still upstairs. Give a me a day or so and I'll crack it open and take some pictures.

NOTE The BX5 is a completely different beast inside, but lets see.

Joey McGowan said...

Thanks man appreciate it.

Mr Ives said...

Hi Joey, have posted some extra pictures and a description of where I *think* the wires all go.


Hope this helps

Joey McGowan said...

Thanks a million. Appreciate you taking the time to post more photos.
The layout seems to be a bit different to the one I have so it's still a bit tricky to work out which wire goes where. I've emailed M Audio I'll see if they get back with some info. Thanks anyway

Dude said...

Hello mr. Ives, I`m considering
buying BX5`s and I`d like to know
which chip amps are in hf and lf outputs?

Mr Ives said...


Good question. I didn't take note at the time. Looking on some diyaudio forums i posted on there was a discussion that the BX5s used either TDA2020 or TDA2052. Note my primary repair was of a BX5a and the BX5 i subsequently got, i couldnt repair. I still have a single BX5a i could crack open and take a peak, you can almost see the writing here

Anonymous said...

Thanks, yes, my bad, I meant BX5a`s,because today in my country only avalible model is BX5 D2 which is i think very similar to BX5a model
(amps are probably the same).

It looks like tda 2052 yes and
some guy here in comments confirms it.

@TeamBrickSquad said...

Purchased these speakers about 2 years ago but never opened them until yesterday and today I purchased the trs cords to connect to my laptop after all that I found out that one speaker is louder than the other. What should I do about this?

Mr Ives said...

Hi TeamBrickSquad,

The fix in my blog is specifically for two problems, one is loud hum, the other is the complete loss of the bass from one of the speakers due to poor soldering on the bass driver. You sound like you have a different problem altogether.

well I'd try a few things first to try and localise the problem :

1) Each speaker has its own volume control on the back. Check these are both at the same level

2) I'd try playing some music from a different source i.e from a CD player or an iPod, iPhone etc through the speakers to see if the problem is still there. That way you can rule out if the problem is something local to the computer. Computer sound has lots of places where you can set volume, equalisation and Balance. In windows you can often set it in control panel sound, at the sound card level, on the task bar and in the app for example iTunes. Any one of these places might have the balance set slightly to one side. Trying a different source might flag up if its the computer that is the culprit.

3) if you swap the cables over , does the loud speaker swap too ?

4) Even though one speaker is louder, does it sound right i.e if you listen close to the speakers tweeter and bass/mid, are you getting sound out of both and does it sound right i.e not distorted.

It would be worth trying these first. The fix I describe in the blog isn't going to help unless the problem is the complete loss of one of the drivers in the quieter speaker and that doesn't seem like what your describing. Try the tests above and tell me what happened

John said...

Thanks so much for this post! 20 minutes of work and $10 later my one dead Bx-5a is working perfectly again.

the one thing i noticed when i first put it all back together and the monitor wouldn't power up, the green ground line coming from the transformer that was screwed to the heatsink was just a LITTLE loose. i hadn't managed to screw it down tight enough. that was all it took to make the unit not power up.

as soon as i tightened it and put things back together, everything was a-ok. i'm probably going to buy 2 more caps and replace them in the other speaker, just as a preventative measure, since i'm sure eventually those will fail too. thanks again!

Mr Ives said...

My pleasure John, glad the fix worked for you and thank you for the info about making sure the ground wire is tight. I think its a good idea to replace the caps in both speakers as the second is likely to fail, and why not strike while the (soldering) iron is still hot and the steps are still clear in your mind. The only other thing id add is the mystery of the tweeter phase, as i mentioned in the blog, the pair i worked on had the tweeters wired differently,possibly a fault with that pair, but ive never really figured out which way was right. If your are both wired the same , as they should be, then i think you're ok

Anonymous said...

Thank you Mr. Ives, for posting this, lo, these many years ago. Nothing ever dies on the Internets!

My BX5As quit after 7 years of daily use. The 6800 ūF caps looked perfectly fine, but knowing the capacitor problem of the past decade, I figured it was worth $11 USD to find out.

Taking the suggestion of another poster, I used caps of 35V rating. They were physically larger, but the leads were the same offset.

Your pictures of disassembly were most helpful; for me, that was the hardest part of the whole replacement. I was surprised how easy the solder on the caps came off with a solder sucker; solder braid was ineffective.

All this time, I thought the thump on power on was the result of my mixer's output. Now I know differently. Back in the day, I'd throw on a toroidal choke to quell the thump.

For easier access to the main board, I removed the screws holding on the XLR, TRS, heat sink and volume pot. Dead nuts easy to have a flat plane for the desolder work. If you do so, only the legs of the output transistors are holding onto the heat sink, so work gently.

I agree with you that the build quality was poor. My defective LED power light was never soldered, only heatshrunk!

Off to disassemble the other speaker. A tip of the hat to you for your evergreen post! Again, my thanks!

Mr Ives said...

Thanks Anonymous for your kind words, glad the blog is still of use

dg said...

Mr. Ives-
What a beautiful, comprehensive post. One of my bx5's died 3 years ago, exhibiting the tell-tale big thump on shutdown. Finally got around to making the repair attempt, and the new caps fixed it nicely. Hardest bit was waiting for delivery of the parts. Thank you!

(Now, where did I put those Kinks ...)

Mr Ives said...

Hi dg, thank you for your kind words. I'm very glad this old blog is still helping to resuscitate otherwise healthy speakers.


Anonymous said...

Awesome. Gave me the confidence to open up my BX5a. I'm afraid I gouged the top of the board but we'll see what happens when the replacement caps arrive.

I'll try to remember to update.

Thanks for this information!!

Anonymous said...

UPDATE: (anonymous comment Nov. 2 2014)


Awwwww yeah.

Harp said...

Thank you SO much for this incredible post. I have a BX5a that blows the fuse on power up. Will any of this apply to such a problem? Its time to fix this little guy. Thanks!

Charlie Irene Louverly said...

Thank you .. works great again ..your tutorial is much appreciated!

Mr Ives said...

Hi Harp, short answer is im not sure. A fuse that blows in power up means too much current is being drawn, it could be the caps problem. Did you get any symptoms like him or the thump on power off prior to the fuse problem ?

Harp said...

Its been so long I don't recall, maybe a lil thump. I'm going to change out the capacitors and see what happens! Thanks!

Harp said...

Fixed! This remedy works for the people with fuses blowing.

Mr Ives said...

Thanks Harp, really glad it worked for you and thanks for posting your success

Anonymous said...

Thank you very much for this detailed guide!! These BX5a's are decent little speakers, but boy are the factory caps shite. Replaced em and the speakers sound great again!

Anonymous said...

I ahve seen that as of today, M-audio is selling the BX5 D2, and I'm wondering if they have improved their build quality on this new model. Anyone has an idea about this?

Anonymous said...

The BX5 D2 models have improved capacitors.

4700uF/35Volts are default.

Robert Morrison said...

I have BX5a speaker with a loud hum that I will give to anyone who will pay the shipping. Thanks Bob

jdb said...

Brilliant! Bought some caps on eBay and had mine repaired in less than an hour. Scratchy audio has been banished!

Mr Ives said...

Glad to hear it jdb, and thanks for sharing

me said...

Thanks for posting this. I've replaced the capacitors with these. The repair went smoothly, except that the solder pad came off after de-soldering. I re-soldered the long cap leg to a pad nearby that's connected to the same PCB plate. Continuity checks are all fine.

Unfortunately, no matter the volume input, I get a 120 Hz buzz. The output from the capacitors is as expected—4.6ish V DC with 30mV or so residual ripple current from the 60Hz (US) mains power—but there remains a loud, 120Hz buzz independent of the volume potentiometer.

Any thoughts or areas to test? How can I further narrow down the problem? Have you (or commenters) seen anything like this before?


Mr Ives said...

Dear me, sorry that the repair has not yet worked. Is this behaviour seen on both speakers or are you just repairing one ? 120Hz is twice the mains frequency , and is what I'd expect off the un-smoothed output of the Bridge regulator. This suggests to me that , for whatever reason the smoothing caps are not working as they should,. You sound like you know what you are doing, so I'm sure they are the right way round , and I guess they shouldnt be faulty ?

Quint said...

Thanks for your response on such an old post, Mr. Ives. It seems you are the resource on BX5a repair.

This is just one speaker. Exactly, my first thought was that the output from the bridge wasn't getting smoothed by the capacitors, but it actually is. It's giving a strong, 4.6ish V DC signal with very small ripple voltage across the caps, if I remember correctly. Because of this, I doubt the caps are faulty. My current hypothesis is that there's a short somewhere, perhaps at one side of the bridge. I had to solder a capacitor to a different hole, since de-soldering didn't go quite as well as planned—I went with the trick of bending a cap leg to the nearest solder point connected to the same PCB plate. I'm quite sure they're connected, as continuity checks seem to agree.

Also if I remember correctly, an oscilloscope connected in place of the bass driver shows output that one would expect on the output of the rectifier bridge—a function like abs(sin(x)) at 120Hz.

I'll need to go back over to the lab to make more measurements on it. I'll try to make a trace through all the op-amps and transistor amplifiers to see what the output looks like at each step. When I do, I'll throw another comment up. Stay tuned for hopefully some more precise details!

Quint (formerly "me", not sure why Blogger settings chose that)

Kevin Brady said...

Since one of my BX5a's started to make a loud buzz a couple of weeks ago, and the other had some clicks and pops, I'm very glad to have found this blog!

I ordered Panasonic EEU-HD1V682 electrolytic caps from Mouser here in the USA. They are 6800uF and rated for 35V and +105C. As you pointed out, they are a little longer than the originals, but there is plenty of room for them on the board. They were US$3.73 each.

My BX5as are just a little different from yours. For one thing, the power lamp is glued into the bezel (it was fairly easy to disconnect the power to it from the board though) and the woofer is held in place by four of the same Allen headed screws that keep the bezel on. Inside was exactly the same, although removing both the bezel and the back assembly from the cabinets required a little "persuasion", maybe because I've had these sitting in the same place for quite a long time.

I strongly suggest if anyone else does this to use desoldering braid to remove the defective caps. The glue holding the caps to the board on mine was quite brittle and easily dislodged and with the help of the braid I had the old caps - one on each board showing signs of bulging - off in about 10 minutes with the board looking clean and all ready for its new caps.

Everything else was pretty straighforward. (Well, the lower grounding screw to the heat sink is a bit of a fiddle - a long Philips screwdriver helps.) The first BX5a took me a good 90 minutes to do everything but I blew through the second in less than 30.

Anyway I'm thrilled to have fixed these for under $20. I use them as monitors for my desktop PC and this has saved me at least a couple of hundred dollars for new ones.

Thank you for taking the time and sharing your expertise with this blog.

Kevin Brady - Somerset, New Jersey.

Mr Ives said...

Hi Kevin,

I'm really glad this old blog is still of use, and delighted it helped you.

Thanks for the added detail regarding variations in the LED and woofer arrangements within the production run of these speakers.

Thanks for your kind comments

best wishes


natcho said...

Hi this post is incredible. I've been sitting on a pair of bx5a for years not really know what would come of them. I was wondering whether there is any additional safety precaution aside from disconnecting from the mains. Thanks!

natcho said...

Hi this post is incredible. I've been sitting on a pair of bx5a for years not really know what would come of them. I was wondering whether there is any additional safety precaution aside from disconnecting from the mains. Thanks!

Mr Ives said...

Thanks Natcho,

Once the speakers are disconnected from the mains and the internal caps discharged then they are safe. Basically pull the mains wire out and wait for a few minutes with the switches on the back still on

natcho said...

Thanks that's ace!

John B said...

thanks so much for this article Mr Ives!

i have a pair of BX8a Deluxe's (the bigger brothers) and one has decided to crap out on christmas eve. same symptoms i believe as what has been stated in the article and comments:

- normal low volume use.
- suddenly the speaker goes into overdrive and sounds like a loud bassy trainwreck.
- i switch off in a panic and try to flush the power and try again.
- pops back into life for 20 seconds, then goes nuts again.
- now i only get 60hz full throw as the sub cone is being forced outwards in one phase.
- signal provided to the speaker isn't passing through the sub nor the tweeter.
- power led and unit power still seems to be functional.

I opened it up and had a look hours before stumbling on this article, i was looking for leaky or bulging caps, but couldn't see any, pics below:

my board seems to have a lot of caps of varying sizes, twin 2200uf 35v caps, and a larger 4700uf 50v cap, and a previously bodged larger but same rated 4700uf 50v cap is omitted in the photos but sits on the underside of the board, i can see a white wire across its terminals and residual glue from where it used to be, the previous ebay owner must've not been able to fit it on the original side.

reading from the comments some people said although their caps didn't visibly show failure, replacing them fixed it, it could also be that the caps have leaked from the underside and you'd never see cause jimmy went mad with the gluegun in the factory.

I'd like to just be ask ya and be sure before i order the caps and take on the procedure:
- are the symptoms similar to your experiences/diagnosis of faulty caps?
- am i looking for the largest set of capacitors to replace? replace both 2200 + 4700?

i'll likely replace caps on both units as i want them to sound the same

no multimeter at hand for diagnosis but plan to borrow one from my father tomorrow, i've only got a soldering iron so de-soldering while also getting all that glue off could be extra difficult.

when i get the multimeter i can run some tests if you have any tips.
Many thanks again, thank god there are people like you who don't just throw away goods!

John B said...

thanks so much for this article Mr Ives!

i have a pair of BX8a Deluxe's (the bigger brothers) and one has decided to crap out on christmas eve. same symptoms i believe as what has been stated in the article and comments:

- normal low volume use.
- suddenly the speaker goes into overdrive and sounds like a loud bassy trainwreck.
- i switch off in a panic and try to flush the power and try again.
- pops back into life for 20 seconds, then goes nuts again.
- now i only get 60hz full throw as the sub cone is being forced outwards in one phase.
- signal provided to the speaker isn't passing through the sub nor the tweeter.
- power led and unit power still seems to be functional.

I opened it up and had a look hours before stumbling on this article, i was looking for leaky or bulging caps, but couldn't see any, pics below:

my board seems to have a lot of caps of varying sizes, twin 2200uf 35v caps, and a larger 4700uf 50v cap, and a previously bodged larger but same rated 4700uf 50v cap is omitted in the photos but sits on the underside of the board, i can see a white wire across its terminals and residual glue from where it used to be, the previous ebay owner must've not been able to fit it on the original side.

reading from the comments some people said although their caps didn't visibly show failure, replacing them fixed it, it could also be that the caps have leaked from the underside and you'd never see cause jimmy went mad with the gluegun in the factory.

I'd like to just be ask ya and be sure before i order the caps and take on the procedure:
- are the symptoms similar to your experiences/diagnosis of faulty caps?
- am i looking for the largest set of capacitors to replace? replace both 2200 + 4700?

i'll likely replace caps on both units as i want them to sound the same

no multimeter at hand for diagnosis but plan to borrow one from my father tomorrow, i've only got a soldering iron so de-soldering while also getting all that glue off could be extra difficult.

when i get the multimeter i can run some tests if you have any tips.
Many thanks again, thank god there are people like you who don't just throw away goods!

Mr Ives said...

Hi John B,

I'm not sure. if you are getting 60 Hz through the bass speaker that suggests that your PSU smoothing caps are not functioning, and these are the caps I replaced in the article. However with the BX5a the speakers carried on working, there was just loud hum. Do you also get the loud thump when you turn off the speaker via the rocker switch.

I'd love to tell you I'm confident that this will fix your problem, but I'm not sure. I had a bx5 (not bx5a) where I think the problem was probably something in the chipamp and thats beyond my abilities to diagnose. Possibly the BX8 is based on a different chipset ?

Its a lottery. I think I'd be tempted initially to just replace both of the large 4700uf caps with components which will fit on the board correctly, so you need to ensure the right (or better voltage), capacitance, diameter AND pitch . That way you minimise your investment to just a pair of caps, which shouldn't be too expensive. The Cap length may not be an issue, but you need to check the clearance.

You'll need to remove the bodged one from underneath and the original one and clean up all the glue, being careful not to break or raise any tracks or other components, the glue spills over a ceramic cap and a few other things. As long as its clear so the new cap can seat correctly, dont be tempted to bodge it like the previous guy as that circuit board will vibrate when in use and having the full weight of a cap hanging by its leads is not good for joint integrity.

I found very carefully using a craft knife (Xacto type) is god for cutting round the cap and getting the worst of the glue. You just need to ensure the old cap comes off and the new cap fits neatly

if that fixes it then repeat for the other speaker.

if not then maybe look at the 2200uF, but they look like they will be harder to remove, being located quite centrally. It looks like you have two separate power supplies as there are two sets of cables from the transformer and what appear to be two large bridge rectifiers. Possibly the speakers are bi-amped with separate amplifier circuits nd smoothing for the bass and tweeter. Or one power supply drives the inputs i.e all the opamps that handle the buffering while another powers the amplifier device - there are two devices connected to the heat sink. Possibly tracing the wires back from the speaker cones might provide a clue

I'm sorry I can't be more positive , these are complex devices and I have not seen any schematics for them.

I wish you the best of luck .

Casey Finley said...

This is the most detailed info for fixing these monitors. Years after my first BX5a speaker went out, I finally got up the courage to pull it apart and fix it with this as my guide. Works like a champ now. Thanks!

Mr Ives said...

Thanks Casey, glad the blog is still useful

Anonymous said...

I'm experiencing a very weird kind of problem.The audio from one speaker goes off with a pop then comes back again with another pop.The blue LED remains functional all the time.This has happened alot of times.Any suggestions What it can be?

Mr Ives said...

Hi, Not sure, this doesn't sound like its the Power supply caps. Are your speakers BX5a's ? When you loose the sound, do you loose it from both speaker drivers i.e the tweeter and the woofer ? is there a repeatable sequence that gets the sound back i.e cycling the power to the speaker ?

Anonymous said...

Mine is BX5 D2....Yes i loose from both drivers....Nopes.....Sometimes its goes out for like 5 Sec....sometimes even for like a Minute....Cycling the power doesn't help.....

Mr Ives said...

OK, well It doesnt sound like the supply caps are the issue.With failed caps the BX5a seems to work, it just has loud mains hum too.

I guess you are out of warranty ?

Anonymous said...

Thank you so much for this informative description on how to repair the BX5a smoothing caps. I was able to successfully perform the repair on my BX5a speaker this past weekend and would have never attempted the repair not for your post. I wanted to add a helpful tip for anyone embarking on this repair. I was using a 25 watt solder iron and copper de-solder braid for the 1st half of the de-solder portion of the repair, but it was slow going and not very successful. I went out and purchased a 60 watt solder iron thinking that maybe I needed more heat to fully melt the solder into the braid. It worked like a charm. 60 watts gave me the extra heat I needed to wick away the remaining solder into the braid. FYI...I used the same Panasonic EEU-HD1V682 electrolytic caps from Mouser (In the USA) that the poster earlier in this forum recommended.

yatess said...

One of my BX5 speakers is getting much hotter then the other, in fact one is hot and the other is room temperature to the touch. You can't keep your finger on the hot one because it'll burn you, really!
I've replaced both TDA 5052 ICs (the ones that are attached to the heatsink) and two 4700uf/35V caps that were swollen, and temperature problem is still the same. I have no schematic, reference voltages or parts list for this speaker so it's hard to troubleshoot. Visual inspection and guessing are the only techniques I've used so far.
Does anyone else have this problem? Better yet, has anyone found a fix for this problem.


Traysi said...

Thank you so much for posting this information in such detail. I just fixed my old right BX5a's that has been buzzing and popping for years -- just as in your original case, it was a matter of the failed capacitor. Cheers, from St. Louis, MO, USA.

Mr Ives said...

Thanks Traysi for your kind words, glad it helped you.

John B said...

Thanks so much Mr Ives,

I was the one with the bigger BX8a amp that died. Sorry my reply and thanks has been quite long in the making, but thought I'd post my results here.

I bought and replaced the twin 4700uf and 2200uf caps sadly to no avail, same behaviour as before, at that point I looked for an audio HW repair shop near my work. They diagnosed and found it was the IC (integrated Circuit) chip and a resistor that was faulty and replaced. All in all about £105 spent but sometimes you gotta respect the expert's work! And pay them, I'm glad it's fixed.

I'd also like to post a schematic I found for the BX8a's, might help someone else here:

I'm moving country now so selling them after all that, but atleast I can sell as a pair.

All the best, JB

yatess said...

I have a pair of BX5de monitors. One gets very hot, too hot to touch. I've changed suspicious looking caps and the two power ICs that are attached to the heat sink but the problem still exists. I would love to find a schematic for my model. The BX8a isn't the same as my model. Right now I keep the faulty speaker powered down until I need to hear a stereo image. I have the speakers installed in a FCPX edit suite through a M-Audio Fast Track C400.


Gonzalo Nuñez said...

Thank you so much for the post. I've bought these monitors last february in NY and brought them home (Argentina). Yesterday I decided to set up a home studio and I unboxed them. One of them powered on but had no sound. I opened the speaker and one of the capacitors was swollen and leaked a caramel-looking fluid. Also another electgronic part (I don't know if it a capcitor) is burned and this affected the board also. I will attempt to fix it by replacing the faulty parts and tell you how it goes. Thank you so much for taking the time to share this information with us. Regards!

Gonzalo Nuñez said...

Thank you so much for the post. I've bought these monitors last february in NY and brought them home (Argentina). Yesterday I decided to set up a home studio and I unboxed them. One of them powered on but had no sound. I opened the speaker and one of the capacitors was swollen and leaked a caramel-looking fluid. Also another electgronic part (I don't know if it a capcitor) is burned and this affected the board also. I will attempt to fix it by replacing the faulty parts and tell you how it goes. Thank you so much for taking the time to share this information with us. Regards!

Gonzalo Nuñez said...

Hi. I have just realized that I bought the 6800uf 25v and my bx5 actually has 4700uf 35v. Installing the 6800uf 25v would be risky, right? Thanks.

Mr Ives said...

Greetings Gonzalo,

risky ? No , but there are 3 concerns with using the wrong spec

1) voltage 25v will work fine, going for a higher value gives you a bit of extra margin. The originals were 25v and I went with 25v

2) Capacitance. The additional capcitance should be fine. It can deliver a little more current, but its not significant

3) Size. If the capacitor is a bit longer (bigger uF) there should be room. The main issue is the pitch, which is the gap between the wires emerging from the cap. Its important that they are the same as the capcitor needs to sit tightly against the board. the wires should pass striaght through the board, and not be bent or the capacitor sit too far from the board. if the pitch is the same, then I think you will be fine

Unknown said...

Hi Mr Ives. Thanks for the article and for tending to the comments after all these years.

I used your guide a few years back to replace faulty caps in both of my BX5As which developed the thump within a few months of each other.

Recently one of my speakers started to distort and rattle on transients and anything above moderate volume.

Suspected the caps so I opened it up and sure enough one of the large caps, the one which I hadn't replaced earlier, was a bit of a mess.

I tested the speaker with the cap fully removed and it behaved pretty much the same as it did before I removed the cap. This suggests to me that I am probably correct in assuming the cap is to blame.

Unfortunately in removing the capacitor I accidently took the solder pads off the pcb so I am currently unable to replace it.

Would you have any tips on how I should go about repairing the damage to the PCB?

Many thanks,


Mr Ives said...

Thanks Joe, glad the blog is still of use. OK, I agree it sounds like your assessments is correct. I guess it depends how baldy you damaged the copper tracks. I have in the past doen the same, and repaired the tracks with lengths of wire, for example off cuts from the capacitor leads to bridge removed sections or used insulated wire where I had to cross another track. You need to be very careful, as my disclaimer says, as these units contain full mains electricity, and also any damaged or poor wiring can lead to arcing which can cause fires. That said, unless the damage is substantial it should be possible to repair with point-to-point wiring as I described assuming your soldering skills are sufficient. If the copper is removed directly where the cap leads poke through, I think I would also hot glue the caps down as there will be nothing to hold them in place. The copper tracks solder jpint also holds the caps god and steady in position.. God luck, keep us posted

Joe Sayer said...

Hi Mr Ives.

Thanks for your quick response.

I've cleaned up the area and taken a photo.

As you can see I've caused a few superficial scratches and lifted the pads.

In the photo I've marked the positive side, it's printed as such on the other side of the board.

I found a video in which similar pcb damage is circumvented by exposing the copper on the trace / ground plane then connecting the component via hook up wire.

I think I could apply the same technique but I am uncertain as to where I should make my new contact points.

Many thanks again for your advice.


Mr Ives said...

Hi, Well what you could do is buy some hook up wire of approximately the same diameter as the leads on the replacement caps OR buy some thin heatshrink. . Put the new caps in place, use some hot glue to secure them down. then on the reverse side you could fold the long leads from the caps and bend them to reach the nearest existing solder dome but most importantly , that is on the same tracks as where the lead emerged. place some heatshrink or insulation along the wire and cut with just enough bare metal to solder onto the dome. With some insulation on the wire you are duplicating the effect of the paint over the tracks , i.e acting as an extra safety measure should a component come free inside. hence the positive lead +ve could be soldered to the nearest dome at about 5 O'clock relative to your picture. The negative wire could go to a number of points as it looks like the raised piece joined two sections, but the obvious place is to wire it to the negative of the other cap you already replaced, the one with a pig-tail curl in the lead ;) You might need to bend the lead in a few dog-leg places to get it to be in the area. better it touches the new pad without any reliance on the solder to hold, thet way its not under tension.

Just make sure that you have a) insulation on any lead runs and b) youve secure the cap on the otherside to the board

Joe Sayer said...

Is this what you are suggesting?

So if I bent the capacitor leads and soldered directly onto the marked domes this would behave the same electrically as the original solder pads?


Mr Ives said...

It should do,

I cannot be 100% based on the picture, but that appears not to be joining two tracks that were not joined before

Joe Sayer said...

I can confirm that it is joining the the same two tracks together as before.

I will solder the leads to the proposed points, insulate them and secure the cap with hot glue.

I'm showing my inexperience here, but could I in theory scrape away my own contact point around the '-' symbol, solder there and have it form the same circuit? That is to say, does it matter whereabouts on the track I connect, as long as I am connecting to the right track?

Mr Ives said...

You could scrape away, there is no sequence implied here, everything obeys Ohms & Einstein's laws so everything happens no matter of connection point

Joe Sayer said...

OK great, that's exactly what I was wondering, if the particular position on the trace implied a sequence.

I will go through the repair and report back!

Paul Rowe said...

I have 2 pairs of these. I fixed one that had the buzz and the thump when when turning on and off by replacing the caps and it worked perfectly. The second pair i bought off craigslist for cheap since one of the speakers pulsates. Any idea what the pulsating could be? is there a reoccurring problem with the bx5a that pulsate? Thanks!

Mr Ives said...

Hi Paul, what do you mean by pulsate ? Do you mean the sound varies in volume or the bass has some artificial pulsing ?