Technics SP-10 Mk. II drive problem

[Sam Cogley]

The story until now...turntable and power supply recapped (with the exception of one 1uF 50V in the turntable, didn't order enough). Table is speed stable and seems to exhibit no problems at the 33 and 45 rpm settings. Table is running slow at 78 rpm. It's also making what almost sounds like a grinding noise, and if picked up, the table feels like it is "kicking" as the platter rotates. Neither of these problems is observable at 33 and 45. Anyone have a clue what's going on?

[13oots2]

Might well be worth taking a peek at the service manuals available in the Library. http://www.vinylengine.com/library/technics/sp10.shtml

[Sam Cogley]

I have, and I finally got my o-scope working so that I can start going through the troubleshooting steps. Mostly I was hoping to run across someone who has seen a similar problem and would have a good idea of where to start.

[crofk]

May sound trite but start at the beginning and don't skip any steps.

kc

[Sam Cogley]

"Start at the beginning" worked this time! I re-tested the power supply voltages after the recap and found them still out-of-whack...and as it turns out the electronics of the SP-10Mk.II are EXTREMELY sensitive to out-of-spec voltages.

First test results (no load, nominal/actual):
5V / 5.39V
32.5V / 33.12V
140V / 151.5V

For further testing, I connected the trusty ol' Fluke to the power supply, hooked up the table to test things under load, and adjusted the 5V supply so that it was dead-on at 5VDC. 33 & 45 OK, 78 still slow and physically wobbly. Not a logic problem, obviously.

After that I set the Fluke on the 32.5V motor drive line, and dialed it in with the table running. At first the pot didn't seem to want me to get anywhere between 32.42 and 32.58, but after working it back and forth a bit I got it right at 32.5. 33 and 45 good...78...also good! No more wobble!

The 140V line is unregulated and only drives the neon strobe light. This French page has a pretty cool LED replacement in post #5: http://www.ls3-5a-forum.com/phpBB3/view ... ?f=15&t=94

[Sam Cogley]

It's amazing that .62VDC caused so much trouble.

I also find it interesting that the logic circuits worked fine at 33 and 45 rpm, only going out-of-whack at 78. Could this be a clue as to why there weren't more quartz-lock direct-drive tables with 78 capability?

[crofk]

It's amazing that .62VDC caused so much trouble.

I also find it interesting that the logic circuits worked fine at 33 and 45 rpm, only going out-of-whack at 78. Could this be a clue as to why there weren't more quartz-lock direct-drive tables with 78 capability?

YEa, it always amazes me how many times I bang my head against the wall trying to figure out whats wrong and its turns out to be something silly like that. I seem to overlook the obvious, like " well it was just recapped so THAT HAS to be right" I learned when diagnosing from a tech manual
ALWAYS start and the beginning - don't skip a single step. And you know --- it usually works

Good to hear you got it running correctly. They are a nice table.

kc

[Sam Cogley]

I've let it run at 78 rpm for several hours this afternoon. Still steady as a rock.