Studer A810 tape tension issue

[Mikola]

Hello everybody
A friend of mine has purchased A810 recently and faced a strange issue with tape tension.  The tape doesn't move in forward direction (nor in the play mode neither in FF) and moves only backwards in Rewind mode. If during the Rewind mode press Play or FF button the tape moves OK in forward direction and it is possible to adjust the tension force for supply and takeup motors. If I press stop and then Play or FF the tape doesn't run because of very strong tension from the both sides.
And another strange thing: after powering the deck on the display reads 77777 or 33333 and only after that the soft version 2586 appears. I have changed the battery on MPU board but it did not lead to any changes.
Any ideas are welcome. Thanks in advance
   

[stellavox]

I had a similar kind of tape handling problem on two 812's I recently "restored".  Turned out to be a leaking electrolytic "somewhere".  I say somewhere, because realized that out of the dozens of caps in the unit more than a few were leaky, so changed them ALL - including the tantalums.  Fixed ALL the problems the deck(s) had - after checking/resetting the tension adjustments.  Also check that the tape move sensor is generating the correct signals - if not could be a bad optocoupler (available from Mouser).

It's a LOT of work but worth it - a FINE deck - does benefit from an outboard playback pre tho; He He! 

Charles

[Mikola]

I've checked a lot of capacitors, some of them had been changed. Tension sensors had been adjusted according to SM. No effect. I wander what does 77777 display reading mean.   

[stellavox]

How did you check them? - for leakage?

[Mikola]

Measuring capacitance. Some of them measured 60 uF instead of 220 and 30 instesd of 100, mostly blue Philips   

[stellavox]

Per my experience,  capacitance measurements don't correlate with leakage.  And as I mentioned, there were a number of leaky tantalums also.  It IS a lot of work, but not much money and my problems went away.  Start with the computer(and display)-related cards and see if the flaky readings go away - then on to the tape-handling related cards.  Note that there are electrolytics in places other than on the incoming supply lines.

FWIW; I don't have any problems replacing tantalums with "modern" electrolytics - they are very good.  Believe that tantalums were used in a number of places  because they were physically smaller and space was at a premium.  Todays electrolytics are half the size that they "used to be" and fit very nicely.

Charles 

[Mikola]

Thank you Stellavox
I'll check all capacitors at spool motors control board