Sony PS-X45 turntable spins backwards in stop mode

Chet1

Member
2019-11-19 2:10 am
Hello!

I have unusual problem with the Sony PS-X45: when powered on it immediately starts to spin the platter backwards. When I press start - it starts in right direction, holds the speed, all the buttons and indicators works as they should. Even the crystal lock works fine. But when stopped it starts to spin back again until powered off.

I have a service manual (schematics attached) and a scope, but unfortunately have almost no experience at fixing electronics of that level of complexity.
Full service manual is available here: SONY PS-X45 Service Manual download, schematics, eeprom, repair info for electronics experts

So, do you have any thoughts where to start digging?
 

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Chet1

Member
2019-11-19 2:10 am
Thank you all for your advice. I have some not very good news.


I tried to adjust gain/offset as you recommended using the guide from the manual (pic attached).


At the point 2 I have no AC voltage except some high frequency noise and about -1.5V DC on pin 1 of IC102. Adjusting the 50K resistor has almost no effect on voltage. The backward rotation slows a bit when I connect that shunt but does not stop.


However, I tried to adjust all the RVs mentioned and got something very close to the values in the manual, but with no significant positive effect - it still rotates backwards (a bit slower although) and accelerates when I remove the shunt...



So, what do you think should I try next?
 

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