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,

If it comes to that, I like what Steve Dobbins did to Mike Lavigne's Mk3, removing the motor entirely from its chassis and imbedding it in a solid plinth. I would be reluctant to do that with my Mk3 for fear of diminishing its value, and because it was NOS when I got it, kind of an historical object that also plays music. This did not prevent me from going all out with the plinth design and construction, however. I have held off on the Thalmann mods because of cost. Eventually, I will likely cave in and get it done. The Cotter and certainly the Kaneta mods pertain to the Mk2 only, I think. Also, I think Halcro's objection to the SP10 construction is relevant more to the Mk2 than the Mk3. (Maybe that will get a rise out of him.)

So, can you say what turntable(s) you do favor at this point in time? I myself am not ready to say that the Mk3 is clearly a winner vs the tweaked L07D, at least not yet. For sure, I could live happily with either one.
The Dobbins treatment is not an irreversable step. He did the same with one of my mkllls and sent me back the chassis housing which can be reinstalled with about 3 bikes work he tells me. Not that I ever will but good to know. It's a great performer in it's current form. I also am soon sending my other MKlll to Bill for the Krebs mods so within a month ro two can compare. I expect roughly equivalent performance. We'll see.
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 .