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,

Not offended at all. I have learnt a lot from the various verbal jousts. I'm a great believer in learning what not to do is equally as valuable if not more so in learning what to do.
I dont dislike the SP10mk3, for me the jury is out until I can hear one in my own system. Its on my to do list.
The SP10mk3 upon which Alberts latest mods are based, last I heard it, is mounted in an acrylic/lead/acrylic sandwhich, runs an ET2 heavily modified with custom acrylic manifold & other tweaks, and Shelter 901. The main issue for me are the speakers, Acoustat 2+2 heavily modded in a room that is barely 10ft square. The system in question for me lacks timing, cohesion and transparency but as you know this is a sum of the parts and I would not necessarily ascribe this to the TT.
Albert in an earlier post alluded to power supply mods, and not including the bearing mods, hence the confusion. I cant give you any more insight, but in terms of product improvement in general, you just keep working on the weakest points. It would appear that the latest mods as you mentioned above are more around stiffening up main chassis and mounts.
It would seem to me that reviewing the Kaneta and Cotter mods are quite thought provoking. Looking at the cross section Halcro provided a link to indicates that perhaps opportunites exist to not only stiffen up internal mounts, but decouple or eliminate as much as possible from the main bearing and motor.
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.