Pioneer PL12D service - revisited

I'm delighted to receive messages from readers who have found my Pioneer PL12D blog of use. I recently received this article from a correspondent - Dirk Sipes, and wanted to share it. His approach is that of an engineer, rather than my amateur efforts, and there are some very interesting  details around things like bearing material and the nature of the suspension springs. He has also owned the deck for 40 years since new, which speaks volumes about both their quality and his care.

Here it is :


About me:

Readers be aware that I have tried to use names for parts as they appear on the service schematics for the PL-12D that are available on VinylEngine.com, thus bushings referenced in the blog are what I call cushions, etc.  Also, I have provided some locations where products that I used can be obtained.  Those businesses do not even know I list them, and my use does not necessarily represent an endorsement, although I have found them to reputable.  My thanks to Mr. Ives for helping me to post this.

PURPOSE

I am undertaking the servicing of this turntable because I do not like the sound I get when listening to it through headphones.  There seems to be an underlying low frequency hum, not the 60Hz power hum, but something irritating nonetheless. ( I use Sennheiser HD-424 and HD-598 headphones.)  Also, I recognize that the resurgent interest in vinyl is bringing this turntable back into vogue, and that many new owners have no idea what the provenance of their units are, or what an original really looked like.  I take this opportunity to provide a glimpse into the original presentation as delivered from the factory.

PROVENANCE

I bought my Pioneer PL-12D II in 1968 in Ontario, Oregon, USA.  The cost was $100, which in today’s  money represents $735 in buying power.  I am the original and only owner.  I have never before opened the deck of the turntable, sufficing to service it from the top with oil, belts and high viscosity damping fluid.  I have cherished this fully manual turntable, and have only one other, the semi-auto version.  I’ve used it for 40 years mostly to transfer vinyl recordings to cassette tapes and later to digitize (gasp) my vinyl records.  So It’s not heavily used, just constantly lightly used.  I know that some readers will disbelieve that after 40 years the grease is still viable, the foam was not crumbly, the rubber bushings were usable, etc.  All I can say is that it has always been part of my stereo system, lightly but constantly used, oiled once in a while, never stored away, and it has seen the demise of 4 belts which were replaced before they caused damage. I have replaced the original Shure ceramic cartridge.  Other than the belts and the cartridge, it’s original, and the good condition of the parts testify to the quality of the manufacture, assuming that the environment in which the unit has been located is clean and moderate temperature, such as has been my living quarters.

ON THE OUTSIDE

A sticker on the back says, “Pioneer, model PL-12D-II, stereo turntable, 120 volts, 11 watts, AC 60Hz, Pioneer Electronics Corp, made in Japan, serial No. VD32063MP”.  The turntable was provided with a dustcover, rubber mat with silver decorative ring to cover the platter, an adapter for 45 rpm records, a vial of oil (long since gone, but I remember it being about the viscosity of sewing machine oil), an original rubber belt also long since gone, a small screwdriver and a ceramic cartridge labeled “Shure RS-8T  R1000EDT Realistic”.

INITIAL LOOK INSIDE

I opened the deck, as Mr-Ives does, except using a metal paint can opener with its hook to pull up in the front locking slot, as I did not want to put too much pressure on the plastic control levers, and my deck seemed to stick at first.  I loosened the screws in the sliding slots by only 2 turns, slid them inward, and retightened.  I propped the metal deck up with a  sanding belt eraser, a block of rubber 2”x2”x12”, which did good service by not slipping no matter where I placed it.  

WIRING

The wiring is set up for single frequency 60Hz input, there is no switch to change to 50Hz.  The main power comes in via a 2-wire plug and cord, which attaches to a solder block which hangs underneath the deck near the main spindle shaft housing, the neutral line then going to the on-off switch and then back to the block, the power then going to both sides of the motor.  There is NO ground wire from the mains to the solder block or the motor.  And it doesn’t matter which way the plug is inserted into the US standard 60Hz wall receptacle as the motor turns correctly either way.

Entirely separate from the power wiring, the audio leads are two male RCA plugs from a single flat uni-cable, which has a thin ground wire embedded in between the two signal wires.  These wires attach to a second solder block which is attached under the deck just inward of the tone arm mounting.  The fine wires that attach to the cartridge then route from this second solder block up into the tone arm mounting screw. At this second solder block, the ground wire is connected to two black fine wires that lead to the cartridge, also to the metal deck, and to a metal laminate covering the entire inside bottom of the plinth. Originally, there was no provision to connect this grounding setup into the mains power ground. The owners manual instructed that this ground wire be connected to the GND terminal on a receiver or power amp.  I note this because I know of instances where a lead was connected to this ground wire and inserted independently into the mains third female socket (the mains ground) in an attempt to eliminate hum in circuits where the turntable was being used without a receiver; ie input directly to a computer, or through a RIAA equalizer device such as the USB Phono Plus audiophile computer interface by ART. (Of course, I myself would never attempt such a Rube Goldberg setup….lol.)  I have since come to my senses and connect this ground wire where indicated on a receiver or the external Phono Plus unit.  But I WOULD BE INTERESTED TO HEAR FROM OTHERS ON HOW THEY CONNECT GROUND TO CONTROL HUM.  While I am on the subject of RIAA, one of the reasons I bought this PL-12D in the first place was that it had a ceramic cartridge that output enough voltage to connect to the microphone inputs of a Sony tape recorder.  This was obviously prior to the time I came to understand that to hear the base component of music correctly, the signal from a vinyl record must be corrected via that RIAA curve in a pre-amp or computer program.

SPRINGS

Before opening, the deck was flat with the wood frame all around.  It was springy, but I did not consider it unusually so, and as the turntable usually sits on a weighted shelf mounted to a wall corner and independent of the floor, footfall vibration has not been a problem.  I found the foam buffers inside the springs to be intact, dark grey, not powdery at all, merely deeply formed into the spring.  I did replace the foam, however, as I could not resist trying for the incremental increase in stability reported by others. I found that the light yellow/white foam from a camping pad did well and did indeed reduce the oscillations of the deck slightly.  

On feeling the springs before removing them, it was apparent that they are of different strengths, based on their deflection under the same weight. That the springs are all different is also indicated by the part numbers on the service diagram, where each has a different number (while the foam buffer inserts all share the same number).  Three of the springs also have different colors painted on them, while the fourth is left unmarked.  I tested the springs for strength and the results are below.  I am being particular here, as I know that other owners have shifted the springs around attempting to level the deck cosmetically with the plinth.  In doing so, they may or may not be rectifying what others have done before them, but it will be of interest to know what the original positioning of the springs was, at least on my unit.  IMHO, it is more important to have a certain spring at the point it was designed for, to deal with the mass apparent at that point and its vibrational characteristics, than it is to level the deck for cosmetic purposes, but then I am speaking from the position of having a cosmetically level deck to begin with. Remember that different masses absorb vibrations differently, and I believe the springs were designed to not only support different weights at their respective locations, but also to deal with the different vibrational and resonance damping characteristics of those masses, as well as for damping incoming vibrations such as footfall on surrounding support structure.  It would appear that the solution was simple, but the evaluation, though complex, was completely within the knowledge of vibrational analysis in the 1970’s, even though we were still using slide rules at the time. However, it IS also possible that the springs were designed by some engineering student based solely on the desire for damping incoming vibration (without regard for the resonances from the masses above) while keeping the deck level with the plinth, and in that case I am just blowing smoke, lol.  In either case, I have decided to leave my springs where they were, and just document where I found them for interest.  BTW:  I found only one spring with a rubber washer, at the right front of deck, which was really a rubber layer glued into the hole which accepts the spring. Because other people have found washers in diverse configurations, I believe the washers were used to level the deck, and thus may be a better way to do that than by moving the springs.

The test for strength was conducted by applying 1.5 pounds weight and measuring the deflection. Range of error estimated at 15%. Lesser deflection means stronger spring. Note that the strongest spring is located closest to the heaviest weight which is the motor.

Spring Position Part Number color deflection

right front of deck PBH-010-0 none .20”

right rear of deck PBH-002-A Blue & Green .11”

left rear of deck KBH-149-0 Green & Red .05”

left front of deck PBH-004-A Black .08”

MOTOR

The motor rests on rubber cushions (bushings) which have grooves which allow insertion into the mounting plate.  The cushions were grey but pliable and not crumbly at all.  With the mounting bolts tightened, the cushions do not come into contact with the nuts installed on the underneath of the deck plate, and there is about 1/16” space above the cushion. So the cushions are not compressed by the tightening of the mounting bolts, but only deform slightly under the weight of the motor.

I unmounted the motor but did not disassemble it nor unsolder the wiring. I oiled it with a synthetic clock oil of about 10w as follows:  The excellent photos of Mr. Ives makes it possible to understand that the lower bearing is lubricated from oil held in felt pads near the bearing.  He also said that the rotor shaft could be moved up a small amount to allow access to the part of the shaft inserting into the lower bearing.  So I did what he initially did, only more so, by placing one drop at a time on the shaft just above the lower bearing and allowing it to slowing creep into the bearing.  I was able to place 12 drops of oil there, about 0.2 ml by volume, without any sling out when the motor was started.  I thought it best to try this, knowing that this amount is 4 to 6 times what is said to be used at any one time when lubricating the top bearing, twelve times what Mr. Ives initially tried, and knowing that the tangential force on the lower bearing is considerably less than that on the top bearing, and especially since I did not want to unsolder the power leads at the first solder block or disassemble the motor and face the problems of reassembly.  As for the upper bearing, I placed 3 drops of oil directly into the upper bearing where the shaft fits, and 3 more into the opening leading to the trough that feeds the upper bearing.  At this point, it remained to be seen whether this lubrication would reduce the rumble that I was hearing in headsets when listening to vinyl on this turntable, the main reason for starting this maintenance.

This is a good place to mention that my turntable did not come with a second brass motor pulley with which some units could be adapted to use 50Hz power.  Also, it is interesting to note that where the belt rides on the motor pulley for each speed there is a slight bulge on the pulley.  The center of the bulge is where the center of the belt should be, and the bulge actually acts to return the belt to that location when any displacement occurs, exactly as can be seen on band saw wheels, the pulleys of belt driven machine shops, and the belt drive pulley of the old large steam tractors.  Except when changing speeds, which must be done only with the motor running, the belt must not contact the belt guide (the brass fork which moves the belt up and down).

MOTOR MOUNT RUBBER CUSHIONS

As stated above, the cushions were grey but pliable and not crumbly at all. I revitalized them with LaCrosse Rubber Conditioner, as I did not trust the glycerine idea.  I soaked them for about 90 minutes, and then dried them.  They returned to the original aged grey color as drying finished.  But they were more pliable and soft. The consistency of the rubber is about that of the rubber used in windshield wiper blades, soft, pliable and smooth.

For those whose cushions have become unusable, I have drawn a sketch of the cushion with the DIMENSIONS IN INCHES.  I have no idea how one would be made. 

BELT

I have in the past replaced the rubber platter belt.  So the one I took off was not original. Still, it is interesting to compare it with the new one I obtained from turntableneedles.com (item FBM 23.6 at $10 each plus a little shipping).  The old one was slack, barely staying on the platter when taken off the motor pulley.  It measured about 24.5” long, 0.19” wide, 0.021” thick, and produced a speed of 34 1/3 RPM (yes, thirty-four).  The new one measured about 23 3/8” long, 0.20” wide, 0.020” thick, was much tighter when placed on the motor pulley and produced a speed of exactly 33 1/3 RPM. (Cross my heart and hope to die!) The explanation for this effect will be forthcoming from a better analyst than myself….

CENTER SHAFT

I removed the center shaft from the brass assembly by loosening the set screw 4 turns and pulling the shaft straight up.  There was some white grease on the bottom of the shaft.  Removing the grease revealed a divot in the precise center of the bottom of the shaft.  Microscopic examination showed machining marks within that divot, not the shiny surface of a wear pattern, thus I believe the divot was intentionally manufactured into the bottom of the shaft.  At the bottom of the brass shaft assembly tube was a 1/8” steel ball, also with a bit of the white grease still on it.  The grease was still viable.  The ball had a circular dark mark on it within the grease, which could have corresponded to the sides of the divot in the base of the shaft.  I removed the ball with a slightly magnetized probe and cleaned the brass assembly and the spindle with alcohol.

I know the argument has been made that the divot is the result of wear and should be eliminated by machining the base of the spindle perfectly flat.  The theory is that for minimal friction the area of contact must be minimized.  That theory is not true, as it can be shown that the force required to overcome friction to move one surface across another is dependent only upon the weight holding the surfaces together and the condition of the surfaces, and is independent of the area of contact.  (Google for “friction equation”.)

So why put a ball there?  Why not just place the bottom of the shaft against another flat surface?  Well, the problem of mating two flat surfaces is expensive, as any variation between the two would cause a variation in the angle of the spindle every revolution, which could cause the platter to wobble as the spindle would be constrained only by the walls of the brass shaft assembly tube, and there has to be some gap there to allow for insertion and lubrication.  Also, the ball is preferable not because it’s cheap, but mostly because when lubrication enters the picture it’s a “horse of a different color”, especially when considered over time and with extended wear on mating surfaces, and considering just how the lubrication is applied. Lubrication changes the nature of the surface of the mating material.  But to do that it must be present.  Some mechanism for providing it must be designed.

Consider a flat surface contacting a spherical surface with a layer of lubrication (grease) in between.  As the surfaces make contact, the grease is pushed aside, because contact is made at an almost infinitely small point. Even as deformation occurs, the grease is pushed further aside.  Any positive effect of the grease being present can be realized only if some of it has been absorbed into the molecular or crystalline structure of the surfaces, or remains within surface imperfections (admittedly, both conditions are useful).  Otherwise the grease is not present in the contact area in a major way.  But still, lubrication is important in friction reduction, so a way of providing it long term is desirable, and in a better way than depending upon what might be stuck in a surface imperfection.  I think the divot idea was remarkable.  

The divot does not have to be perfectly smooth nor a match for the spherical surface, in fact it must be deeper than the surface of the sphere can reach, for this idea to work.  So the sphere makes contact with the shoulders of the divot, and the deeper recesses of the divot can act as a reservoir of lubricant, which is trapped above the sphere and is forced out into the contact area only as wear allows the sphere to reach deeper into the divot.  So the grease is actually pumped out to the area where it is needed over time, on the shoulders of the divot.

There is a caveat:  I am considering replacing the existing ball, which has mated with the divot through wear, with another ball (albeit of smoother surface texture) which may not precisely match the shoulder of the divot.  And to make matters worse, I’ll do all I can to reduce the friction and wear between the two so the time required to mate the two exactly will be extended.  But when I look at the surface of the old 1/8” ball and see all the microscopic imperfections in it, and compare it to what I plan to put in its place, I am willing to take the chance.

BALLS

So I went looking for a better ball.  Now the Chinese have 1/8” balls by the millions, and cheap too, and that’s what may be available so readily in bike shops.  But in my heart I couldn’t trust the specs. (Really, they advertise grades of G5 for chrome steel balls at a cost of just pennies.)  So I found a company called “BC Precision”, which described itself thus: “We are a small family owned & operated company located in Chattanooga, Tennessee that specializes in precision balls. We were founded in 2011…”  IMHO if a small company is going to compete with the Chinese, it is going to have to have good service and good quality.  Their website shows 1/8” chrome steel balls available in Grade 25.  But I wanted better, and settled on their “1/8 inch ZrO2 Zirconium Oxide Ceramic Ball Bearings G5”. That’s right, a ceramic.  BC Precision says it more resistant to fracture than chrome steel and doesn’t even need lubrication, but also that grease won’t hurt it.  When examined microscopically, the surface of the ceramic is orders of magnitude smoother than the surface of the original ball, and it rolls quieter and straighter on glass too. So that’s what I’m using.  (And now the reader knows just how picky I can be….)  

BTW:  BC Precision website indicates that their carbon steel balls are often used in semi-precision bearings and in bicycles (so carbon steel balls may be what is available in bike shops) and that these carbon steel balls are G1000, much rougher than the G25 chrome or G5 ceramic.  Also, in carbon steel, the closest they make to 1/8” is 3mm.  So my choice really was between the Chrome or Ceramic.

The microphotographs below show the old ball, compared with new ceramic G5, chrome steel G25 and carbon steel G1000 balls, all illuminated by a half moon light from the right, and held to a slide by a drop of white grease in the background.  The image of the light can be seen reflected at the 3 o’clock position in the new white ball, but is diffused to various degrees by surface pitting in the other balls.  Keep in mind that under a microscope, a shiny metal surface can look dark unless light is reflected directed from it into the lens system, but the translucence of the ceramic seems to allow it to look more true to life. Also, the edge of the balls in the photos looks fuzzy because the focal plane was set to be at the reflection of the light source.

     

The grease left in the shaft assembly was white and nearly the same viscosity of a sample of old Lubriplate Aero that I had.  I contacted the Lubriplate company and was informed Lubriplate 630-AA would be a better match for my application, as Aero was made for aircraft use at altitude and thus low temperatures, so I procured some of the 630.

I placed a drop of grease on the bottom of the spindle and pushed the ceramic ball into it, and letting the grease hold the ball in position, I inserted the spindle into the brass assembly. As there was not yet any oil present, the spindle did slide into position with only a little difficulty as the air slowly escaped.  I then placed a few drops of light “turbine” oil at the spindle.  Sewing machine oil would suffice.  However, I advise against any kind of engine oil for servicing this turntable, as such oil has additives designed to help the oil maintain integrity at high temperatures, and these additives are not healthy for metal in any other application, strange as that may seem.  Use oil with no additives.  After all this, the platter seems to turn by hand only about as easily as before.  Maybe it will be quieter.

The ball I used can be found at https://www.bcprecision.com/collections/silicon-nitride-si3n4-bearing-balls/products/1-8-inch-zro2-zirconium-oxide-ceramic-ball-bearings-g5

If it seems expensive, talk to Cara at customer service, an incredibly nice person, who arranged to send me two samples free.  Grading for balls comes down to variations in sphericity, which also take into account surface imperfections (deviating from both perfectly smooth and perfectly round):

Grade 5 -       .000005" maximum deviation 

Grade 25 -     .000025" maximum deviation 

Grade 1000 - .001000” maximum deviation

THAT’S IT

I attempted no other work on the turntable.  The tone arm bearings seem tight, and the arm lowering mechanism is working perfectly (remember I did service it with damping fluid a few years ago).  The cartridge alignment is still in good adjustment per the built in overhand checker and also third party grid style tools.  So I’ve replaced the belt, the 1/8” ball with grease, and the foam inserts in the springs.  I conditioned the rubber cushions supporting the motor, and oiled the top and bottom bearings of the motor and the spindle.  Let’s see how it sounds…..

SUCCESS!

What I hear when the motor is turned on, but the stylus is NOT in contact with a record is a VERY faint hum, perhaps 10% of what I used to hear, but only audible with the volume above my normal listening level, and this sound has diminished with just a few hours of running. Lowering the stylus to contact a record in an unrecorded portion, I hear the smooth groove noise at least 10 times louder than the motor hum.  Then, when the music starts, even in quiet passages like the beginning of Brahms Symphony No. 2, those noises melt away, and I am once again listening to the music instead of defending myself from grating rumbles.  I feel I have succeeded.  THANKS TO ALL WHO HAVE CONTRIBUTED TO THIS BLOG.

As I did not disassemble the motor, I expect no problems to develop as it runs longer periods.  It should be only better with time.  And now that I know just where to put it (where Mr. Ives put a single drop on the shaft to run into the bottom bearing), I can oil that in just minutes.

BTW:  I did run the motor after I oiled and before I mounted it, and felt just a little fast vibration as I touched the frame of the motor, perhaps from something as simple as out of balance brought about by the set screw on the motor pulley.  I then mounted it and ran it again and felt the same vibration.  I then mounted the platter and connected the belt and ran it again, and felt the same vibration in the frame of the motor.  When loaded with the belt, which applies tangential force to the shaft, I expected the unit to be less vibrational.  This would have been typical of tangentially loaded bearings, which in my experience run quieter under load than when allowed to free float without load.  But the vibration is still there in the motor frame even under load, so my idea about tangentially loaded bearings being quieter under load may not be valid (humility strikes again!) and lends credence to the idea that the vibration IS due to an out of balance shaft. But I do NOT hear anything corresponding to this vibration when listening to a record. Evidently the cushions and the belt to a good job of isolating the vibration from the stylus, and the Pioneer engineers did not go to the expense of precisely balancing the drive shaft of the motor.

PARTS

Original cartridge: Shure RS-8T  R1000EDT Realistic, replaced with Grado XTE+1elliptical obtained a few years ago from NeedleDoctor.com .

Grease: Lubriplate 630-AA .

Ball: 1/8” steel, changed to 1/8" Inch Zirconium Oxide Ceramic.

Belt:  FBM 23.6 from turntableneedles.com, also avail from turntablebasics.com.

Oil: “clock oil” about 10w.  I don’t know where I got mine, but something like it can be had at

     https://www.emperorclock.com/clock-repair/oil-kits

     and “turbine oil” about 5w by Norvey, inc of Santa Ana, CA (sold in hardware stores with a pullout long plastic tube for a spout, located near the evaporative coolers).

Foam: cut from white open foam camping pad, not closed cell nor memory foam.

Rubber conditioner:  LaCrosse Rubber Conditioner from

    https://www.lacrossefootwear.com/rubber-conditioning-spray.html

Supplies: I get things like record sleeves, damping fluid,  etc from turntablebasics.com

EQUIPMENT

Pioneer SX-1050 receiver: this has a built in preamp and is what I normally run the turntable signal into for playing through house speakers.

Preamp for computer:  “USB Phono Plus Project Series by ART” is the preamp and “Audiophile Computer Interface” I use between the turntable and the computer.  I believe there is a newer version, but mine works beautifully.

Headphones: Sennheiser HD-424 and HD-598 open aural design allow ambient sound to be heard.