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Technics SP10 MK3 Restoration

Just got my SP10 MK3 base (motor unit & controller) back from JP at FidelisAnalog.com
JP is one of the most knowledgeable on the SP10 MK3 and is the one who designed and manufactures the MN6042 Speed Control chip that keeps these and other Technics turntable models still operating.

My SP10 MK3 came with the stock Technics SH-10B5 faux obsidian base.
It has very low hours of use , no signs of wear at all on the bearing and not a single blemish, other than some specs of dust and a couple spots on the copper part of the platter that need cleaning.
but I would like to have a 2 arm, constrained layer plinth built and have the motor unit mounted 'naked'. I am presently searching somewhat 'affordable' plinth builders and suggestions would be greatly appreciated.

The work that JP did to both the motor unit and the controller:

1.       Pre-refurbishment measurement to baseline the performance of the unit and to see if there are any underlying issues.
2. Cleaning of all PCBs to remove the factory conformal coating. At~40 years this coating tends to become hygroscopic which can cause stability issues.
3. Physical inspection of all solder joints under an inspection microscope. Many of the joints will exhibit annular deformities which can lead to joint fractures down the road. These must be cleared of the factory solder and re-soldered. There will also be poor joints that need the same treatment. You can’t just reflow as the solder alloys aren’t the same which can also cause joint failure down the road.
4. Electrolytic cap replacement and rectifier diode replacement.
5. Disassembly and cleaning of the motor. Bearing inspection and service work. Proper Anderol 465 oil is used for reassembly. Motor is then checked for any areas of bearing drag.
6. The brake solenoids typically needs cleaned, and band tension is adjusted.
7. Stop/start and speed selection switches in the motor chassis are measured for contact resistance. Too high of resistance is indicative of a switch failure in the future. In the control unit I typically replace all the tactile switches, and the start/stop switch if needed.
8. Relocation of the brake regulator transistor to the heatsink to prevent overheating of the board (factory design flaw).
9. MN6042 replacement installation.
10. PSU ripple check at all critical stages (10).
11.   Course calibration is performed and post-refurb baseline measurements for FG spectrum, motor drive phases, etc. are taken.

12.   After 48-hour run-in final calibrations and verification measurements are performed.

The basic service returns the unit to factory or better specifications (assuming no permanent bearing damage has occurred).   This service is quite exhaustive and very different from the typical work I see of just swapping some caps out, checking some voltages, and adjusting phase tracking.

The advanced service adds on top of the basic service:

1.       Replace all polyester capacitors.
2. Replace drive circuit metal oxide resistors.
3. Replace all voltage regulator ICs and update circuits.
4. Replacement of certain diodes.

Rick


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Showing 6 responses by lewm

lewm
12,524 posts
 
The lunatic billionaires in NYC are typically not New Yorkers by native standards and typically don’t actually reside in their mega-expensive apartments. Of course we know that one bona fide native NYer who is a self described stable genius and billionaire recently moved to Florida.
lewm
12,524 posts
 
I made slate plinths for several of my turntables, or I should say I had them made on a one by one basis, using Pennsylvania slate and a York, PA, Waterjet shop to cut the slabs. The total cost was always less than $500 per. Here we’re talking about cast iron, but the cost to build  vs the retail price for audio products is known always to be wildly out of whack. You pay your money, or not.
lewm
12,524 posts
 
solypsa, There are many aftermarket plinth makers who can remove an SP10 Mk2 or Mk3 motor assembly from its square-ish surrounding escutheon and mount only the motor assembly in a plinth specially designed for that purpose.  I think OMA can do that.  I know that Steve Dobbins was among the first to do that.  Probably others can do that too, for a price.  The process requires re-locating the on/off switch and the speed selector switch to some other outboard location, so it is not for the amateur. 


As to balsa wood, I am a firm believer that the very high torque motors of the SP10 MK2 and especially the Mk3 are best off in a high mass plinth.  Otherwise, there is the possibility for the tail to wag the dog; the very high torque puts a rotational force not only on the platter but also on the motor assembly.  Nature does not care which of the two rotates.  You want the torque to be used to push the platter, only.  So the plinth should be high in mass to resist motion.  Balsa wood need not apply. This is my opinion.  Others may disagree.  That's OK with me.
lewm
12,524 posts
 
For looks alone, the Dobbins plinth is gorgeous. It looks like slate (which Chakster likes to call "graphite") but I think it is made from a synthetic material that has some of the properties of slate/graphite.  For what it's worth, Rich, and I think I have mentioned this before, by ordering my slate slab direct from the quarry, where they honed both sides to perfect flatness and even champhered the corners so as to give it a nice look, and then having it cut to fit the Mk3 by a water-jet company also in PA, I was able to make my slate plinth for about a total of less than $600.  Then I had the solid cherry base made by a carpenter for another few hundred bucks.  I bolted the slate and the wood together for max CLD effect, but gravity really does most of that work. I can help if you want to go a similar route.
lewm
12,524 posts
 
Presumably, you are referring to the cast iron plinth offered by OMA. Just to be sure there is no confusion, I was referring to the slate plinth that has been offered by OMA for many years. I personally would have misgivings about mounting an SP 10 Mk3 in a cast iron plinth, because of the massive magnet that is the rotor.  It would take some convincing for me to believe there is no deleterious interaction between the iron plinth and the rotor that might affect torque, for example. On the other hand, this is such an obvious issue that I have to believe OMA did their homework a priori.
lewm
12,524 posts
 
My advice is don’t overthink it. Nearly all the materials discussed can yield excellent results. I do rate constrained layer damping as a plus, and the mk3 needs high mass, IMO. I used slate and cherrywood. My plinth weighs about 90 lbs I think. ( I never weighed the assembled unit.) My slate comes from the same quarry used by OMA.
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