STUDER A810 SPOOLING MOTOR CONTROL PCB 1.810.760-82

[SonusBonum]

Hi everyone,

I just got my beautiful A810 and it plays like an angel. However after a while and closer to the end of the tape the left tension roller starts wobbling. It is like the tape tension fluctuates in a regular fashion.
I took out the SPOOLING MOTOR CONTROL PCB and checked it. What I found was that C15, C16, C18 and C18 were 220uF/35V while the book says they must be 100uF/25V. Since those caps are in a opamp circuit I figure that these values should be correct. I mean, they are not just for voltage regulation.
Can someone tell me whether the book is wrong or the guy that changed the caps...?
Thank you much...!

Ronald

[Ki Choi]

I would put the original value 100uF 25V electrolytic caps back in the circuit board and check for traces of overheating / cracks on C26, C27, and C28 .47uF 150V rectangular oil caps.  Replace them with modern film type of same value.  These caps will fail eventually anyway.

Ki

[stellavox]

Ronald,

Please let us know if Ki's suggestions fixed your problem. 

I did run in to a similar intermittent problem on an 812 I worked on AFTER replacing the caps you/Ki mentioned.  The 812 has another board called the Tape Deck Periphery Interface, just before the Spooling Motor Controller board you mention .  On the Interface board, Studer revised the time constant on the 812's left tension, hi-pass filter circuit (R43/44 around IC20) from 4M7 in parallel with 6M8 to a single 910K resistor.   This eliminated my problem with large reels but it would still occur (infrequently) on 7 1/2 ips with a smaller 7"reel on the supply side.

Of course the deck probably shouldn't be used with small reels!  But, I happen to have a few of those wonderful, prerecorded remnants from the mid/late 1950's.

Charles

[SonusBonum]

Well, with respect to the spooling motor problem:

I've renewed ALL electrolytic capacitors and the three big paper caps. Changed the 200uF for the 100uF too. Still no change to the wobbeling.
I have professional Weller desolder equipment and resoldered with high quality tin with some silver added to it.
Visually checked the board, the voltages, the test points.

So out of frustration I bought another A810 around the corner and guess what: First changed the spooling motor control PCB. Still wobbeling. Than changed the left motor with the one in the "new" A810: NO PROBLEM ANYMORE...?????

I never ever expected the problem to be in the friggin' motor...?! It turns perfectly. I haven't disassembled it yet.

[SonusBonum]

Oh I forgot: Thank you for responding to my post. It's good to know I am not alone in my R2R adventure... :-)

[SonusBonum]

Hold the phone: not the motor either...! Wobbeling came back. Now I'm angry as a bird...!
Long story short: The brake solenoid wasn't working/moving at all.
That explains the temperature dependency too.

Anyway, finally I can mark this one as solved...!!!

Thank to all for baring with me on this one...