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Author Topic: STUDER A810 SPOOLING MOTOR CONTROL PCB 1.810.760-82  (Read 2419 times)

Offline SonusBonum

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STUDER A810 SPOOLING MOTOR CONTROL PCB 1.810.760-82
« on: May 25, 2016, 02:36:31 PM »
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

Offline Ki Choi

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Re: STUDER A810 SPOOLING MOTOR CONTROL PCB 1.810.760-82
« Reply #1 on: May 31, 2016, 05:13:57 PM »
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
Ki Choi

Offline stellavox

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Re: STUDER A810 SPOOLING MOTOR CONTROL PCB 1.810.760-82
« Reply #2 on: June 02, 2016, 09:29:55 AM »
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
« Last Edit: June 02, 2016, 09:49:46 AM by stellavox »

Offline SonusBonum

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Re: STUDER A810 SPOOLING MOTOR CONTROL PCB 1.810.760-82
« Reply #3 on: June 12, 2016, 02:20:14 PM »
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.

Offline SonusBonum

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Re: STUDER A810 SPOOLING MOTOR CONTROL PCB 1.810.760-82
« Reply #4 on: June 12, 2016, 02:21:55 PM »
Oh I forgot: Thank you for responding to my post. It's good to know I am not alone in my R2R adventure... :-)

Offline SonusBonum

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Re: STUDER A810 SPOOLING MOTOR CONTROL PCB 1.810.760-82
« Reply #5 on: June 13, 2016, 01:20:03 PM »
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...