penmarker
Active Member
I have the turntable above and it had a speed runaway problem. After a while playing it would suddenly speed up and the speed selector or the front adjustment pots wont make any changes.
There were some tantalum capacitors in the servo circuit. Since it happens after warm up i figure it would be heat related and the tants are leaking when they warm up. Vref also goes up so turntable speed goes up. tants get warmer and leak more, vref increases again and so on n so forth.
I replaced all tantalums with tantalums for low leakage except C19 (schematic says 3.3uf but original is actually 0.33uf and i didnt have the value), replaced trimmers, cleaned the front panel adjustment pots
the speed got rock solid.
i got to test it for a week and it held its speed properly. after handing over to owner the speed drift happened again. what could it be?
Attached is the schematic for it. its not the official diagram, i think this person drew it.
There were some tantalum capacitors in the servo circuit. Since it happens after warm up i figure it would be heat related and the tants are leaking when they warm up. Vref also goes up so turntable speed goes up. tants get warmer and leak more, vref increases again and so on n so forth.
I replaced all tantalums with tantalums for low leakage except C19 (schematic says 3.3uf but original is actually 0.33uf and i didnt have the value), replaced trimmers, cleaned the front panel adjustment pots
the speed got rock solid.
i got to test it for a week and it held its speed properly. after handing over to owner the speed drift happened again. what could it be?
Attached is the schematic for it. its not the official diagram, i think this person drew it.