Tape Project Forum
Tape Machines => Tape Tech => Topic started by: SonusBonum on May 25, 2016, 02:36:31 PM
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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
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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
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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
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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.
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Oh I forgot: Thank you for responding to my post. It's good to know I am not alone in my R2R adventure... :-)
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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...