Technics sl-b20 speed issues

bigtuna

bigtuna

Well-Known Member
Greetings. Rehabbing this old turntable. Put new belt, had to Ord new cord. Anyway, it's very clean but unfortunately has sat unplayed for a while . speed is way off. Too fast. Downloaded the service manual deoxed the pitch wheel and the 2 adjustable screws next to the motor pulley. Anyway have adjusted both of them. It's either dead stop or 90 mph. ??
 
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I believe Technics had a processing circuit that adjusted the speeds via the motor.. particularly in the direct driven models.

You may want to get a schematic and post on that particular issue. AKers with more "working knowledge" can help you zero in on the faulty circuit.

Hope all works out!
 
I have this table. You also need to clean the speed selector switch! My guess is that's your issue.

Once you've made sure the trimmers and the pitch and the speed selector have all been cleaned VERY thoroughly. Once you done that, set the pitch wheel as close to center as you can (there's no mark, you have to guess, so just try to get close) and make tiny, tiny, tiny adjustments on the speed trimmers. Those things are very sensitive, just the tiniest movement can throw it off by 5 RPM or more.

At that point if you still can't get it to hold speed you might start looking for bad capacitors and/or the motor.
 
The previous poster's advice is good. And very spot on. Clean the pitch control pots, and speed switch first. If this does not cure the problem, check the power supply voltages and also make sure the electrolytic capacitors are good. If the problem still persists, the servo IC is defective (and it and replacement motors are unobtainable now). I have around a 50% success rate with turntables with this motor currently.
 
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