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Technics SP-10 mkII speed adjustment question

Hi,

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:

"Hello,

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,

Sébastien
128x128sebastienl
chris74
99 posts
 
We also do not provide free technical service but referred the OP to a certified technician we recommend in Chicago for advice. Our certified technicians are not available for free technical advice or assistance. In the event the OP should decide to send in his Mk2 for service, we would obviously be able to repair/service his unit accordingly.

Christopher
Artisan Fidelity
lewm
13,298 posts
 
Sebastien, I am very glad to hear that you got help from Bill. I feel very fortunate that I can get to his shop from my house in only about 30 minutes, and once I get there, I know absolutely that my equipment is in the best possible place for repair. I was rather surprised, actually, when you inferred in your first post that Bill was unable or unwilling to help you; on both counts, I would have expected him to come through for you. Glad to know that this is indeed the case.

Christopher, as I also remarked to Jonathan, I think your position is entirely understandable. I meant no slur on either of you, when I wrote that your respective companies were not "techies". What I really meant by that is that you are not primarily in the business of repair or of offering highly specific technical advice over the phone. If I was wrong even on that level, thanks for the correction.
sebastienl's avatar
sebastienl OP
84 posts
 
Hi Lewm,

I think that I wasn't clear in my first post when I said:

"We already asked Bill Thalmann, Artisan Fidelity and Oswald Mill audio..."

I meaned that we had contacted them, but at that time, we haven't received any answer from them. Finally, I learned that Bill already contact my technician who emailed him before me. Just a bit of confusion there.

Sébastien
sonofjim
557 posts
 
I've worked with both Bill and Chris and have found them both able and affable. I've also corresponded with Jonathan a couple times and personally would never do business with him based simply on his smug and condescending attitude. This is not rocket science and personality counts too.
atmasphere's avatar
atmasphere
11,948 posts
 
Sounds like when your guy looks at the strobe, the act of doing it loads the circuit enough that its unstable. Most 'scopes have a high impedance input (10M is typical) so the loading should not be an issue; this suggests that a device very close to the test point has failed and is barely able to pass the strobe signal.
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