Technics SP-10 mkII speed adjustment question


I'm on my way to complete my Technics SP-10 mkII project. Actually, a friend of mine, a professionnal audio technician, is working to upgrade the PSU, which is done but a small adjustment on the speed must be done and he need some cue on this issue.

We already asked Bill Thalmann, Artisan Fidelity and Oswald Mill audio. Plus, I'll post on DIY Audio today. We'd like to get the answer as quickly as possible to finalized this for the week-end. Hope someone on Audiogon can help.

Here's the message from my technician:


I'm an electronic technician and I do repair for audio equipments, vintage, hifi pro and more. I have a client here that brought me his turntable Technics Sp-10 MKII to fixed. I have a little question about it and he gave me your email because he pretended that you have some experience with this kind of materiel. So, hope that you can response my technical question.

I replaced all capacitors in the power supply and a big solder job. I checked for defect solders or capacitors on the circuit boards inside the turntable and I tied to do the adjustments . Everything seem good right now, the turntable work fine. I tried do do the period adjustment with the VR101 and VR102 potentiometers like in the service manual ( see attachment, Period adjustment method). When I looked the stroboscope at the front of the turntable, It's pretty stable but I can see a tiny rumble at 33 1/2 and 78 speed. 45 is the more stable speed for the stroboscope. So, I fixed the phase reference with T1 at 18us of period and I try to do the period adjustment at the point test T and S on the board with the O point for reference. When I put my scope probe on the T point, I can observe the stroboscope running. It is not stable at all. If I pull off my probe, the stroboscope is stable again. So When I have the 2 probes at point S an T at the same time to do the adjustment, it's impossible to fixed the wave T because it going right to the left on my scope. When I turned the VR101, the T wave going faster or slower but never stable. I tried to ground lift my scope, plug it into the same power bar and try to pull off the reference at the O point. I can't have a setup that I can see a stable T wave in my scope with the one that I can do the right adjustment. Why? Is there a problem with the turntable or maybe it's a incorrect probe or ground setup? Please let me know what you think.

Best regards"

Thanks for help,

Sorry, that's 3 hours work. I'm on a weekend bike ride to benefit MS with my wife and must subconsciously have bikes on my mind.
That's pretty funny, actually.
The main reason I am tempted by the Dobbins approach is that it allows a much wider choice of tonearms. The stock Mk3 chassis gets in the way of most 9-inch tonearms, and on the wide sides (rear and left) one would be hard-pressed to mount and align properly anything but a 12-incher, surely at least a 10-inch is minimum.
That's one of the best things about the sp-10 tables IMO, their flexibility. As far as the desecration of an heirloom goes, I look at these as my long term tables. I bought them to use and if I can do something to improve the performance it make sense to me. I haven't heard a table that sounds better when these are well implemented. I don't believe either Bill's mods or Dobbin's will decrease the financial value. I see Dobbins plinthed MKllls sell for similar prices to the spec variety. It was really the fact that Steve told me the process could be reversed that convinced me to go ahead with his. It's about the quietest most solid table I can imagine. I really wouldn't be surprised if Bill's mods accomplish very nearly the same result. I don't think you could go wrong either way. I'm not sure what table Dover must have if he finds the mklll uninspiring. It must be an awesome machine. Good for him if so. Meanwhile, I can't imagine being happier with my own situation .
I too asked Dover what turntable he currently favors, but the question remains unanswered. I suspect that Dover does not want to get into an argument about direct-drive vs some other technology that he may favor, and I don't blame him. I can only assure him that I am merely interested to know what he likes, because I respect his judgement.
Well same for me. I think that's also interesting to have somebody's reference to better understand any critic formulated.

I too respect everyone choice. After all, they are personnal preferences. In the audio world, you have components for every taste.