Excessive W/F issue on STUDER A710 (REVOX B710)

Tubologic

Well-Known Member
I'm currently working on the repair of a STUDER A710 (similar to the REVOX B710). 1st problem (solved) was that it stopped when engaged to play mode after a couple of seconds. The problem was due to missing (R) Reel table sensor pulses and only needed electrical re-adjustment of the sensor bias pot. Now the deck plays fine and doesn't stop during any mode (PB/REW/FFWD), only at the end of the tape as it should.
BUT... now I have excessive wow/flutter/speed variations issues which seems intermittent and (maybe) more pronounced with some tapes than others. Sometimes it plays very well and the speed is stable, but only for awhile... Pinch roller issues are well know on these models thus I removed and carefully cleaned/sanded them but it didn't made any change. The pinch rollers shows some sign of wear but not enough (I think) to produce such high W/F and speed variations. What else could be the problem ? Capstan motors are running freely and doesn't seem to have excessive friction.
Does the reel table motors (which are know to fail or have bearing issues) and related (sensor) adjustments could have any effect on the W/F performances of the deck ? Are other (mechanical) adjustments or checks needed ? The deck hasn't been re-capped yet.
I was about to order a couple of new pinch rollers (13mm version) but they are quite expensive (over 100$) and I'm not sure it will cure the problem. I have another A710 on my bench with pinch rollers which looks in much poorer condition and there is no noticeable W/F or speed variations.
Any thoughs or help will be greatly appreciated.
 
Well... not much feedback received on this.
After further research work I finally found the problem was caused by a worn out pinch roller, even if it can't be seen by visual inspection it was the culprit.
Strangely enough the w/f issue was only present with some tape brands, and with others the speed was stable as rock. Maybe due to differences in tape thickness or back coating formulation ?
New pinch rollers ordered...
 
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