Bernard GS 431 Turntable: Unstable Rotation, Speed Fluctuations & Performed Repairs

Hello,

I recently dug up in the attic of my father-in-law's old Bernard GS 431. After the initial problems I solved myself I encountered a difficulty I can't overcome. The turntable has extremely unstable rotation. Sometimes half the disc is played correctly and then goes "crazy" by speeding up and slowing down the recording. What I've changed / done so far is:

- belt replacement;
- lubricating the plate axis with technical oil;
- replacement of bulbs and photoresistor under the plate;
- needle replacement;
- electrolyte replacement;
- photoresistor replacement under the plate
- replacement of the potentiometer for speed control;
- replacement of PR1 and PR2 potentiometers for speed regulation (noticeable improvement after this replacement);

At the moment, I ran out of ideas and I reviewed a lot of threads about this series of turntables.
Does any of the forum members have experience that could be shared and directed me to the potential source of the problem? I will be grateful.

Desolder D6, possible malfunction of the flip-flop.

Switch 33/45 to be checked.

Did you also replace these electrolytes in the power supply? Is the diode D2 stable about 10V?
The problem may still be the engine itself.