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Old 17th November 2012, 02:03 AM   #1
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Default A problem with my Revox A77 MK3

Hello

I have a Revox A77 MK3, sr: G170460, two tracks, with 7 1/2 and 15 ips speeds. I did not used it since some times.

I have a problem, wen I turn it on, even wen I did not push any recording buttons, and without any input signal, the vu-meter are topping to the maximum and still topping to the maximum until I turn my Revox off.

And wen I record music or sine signals (7 1/2 and 15 ips ), I did push all the buttons for recording, but there is no sound on the recorded tape (Scotch 250)

All the motors run good.

Any hints or solutions ?

Thank you

Bye

Gaetan

Last edited by gaetan8888; 17th November 2012 at 02:22 AM.
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Old 17th November 2012, 05:56 AM   #2
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Hello

I have take out the bias board and the vu-meter are still topping to the maximum.

I have take out the playback amp board and the vu-meter are still topping to the maximum.

But wen I have take out the 2 record amp board, the vu-meter was no more topping to the maximum.

So, I think it's the 2 record amp board who are the problems.

Which parts on the record amp boards who could cause the problems ?

Thank you

Bye

Gaetan
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Old 17th November 2012, 09:04 AM   #3
AuroraB is online now AuroraB  Norway
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Location: Norway, -north of the moral circle..
I'd start with checking PSU and internal DC distribution, cables, connectors etc.
Seems unlikely both record amps would blow at the same time
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Old 19th November 2012, 06:04 AM   #4
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Hello

I think I have found the problems. I've tests some capacitors with my capacitance meter.

First, the two recording amp C509 electrolytic capacitors, who connect to the vue meters, are short, so dc are going to the two vue meters.

And the record relay circuit C602 electrolytic capacitors are dry and do have near 0 uf, so the relay was not working since C602 need to be full to switch on Q601 and the relay.

I will do more tests, but it seem that I will need to replace all electrolytic and tatalum capacitors in my Revox.

Thank

Bye

Gaetan

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Old 20th November 2012, 09:09 PM   #5
jkorten is offline jkorten  United States
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All of your tantalum capacitors have probably died. Some as a dead short, some open. You would be advised to replace them all. On the motherboard as well as on the cards.
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Old 20th November 2012, 10:39 PM   #6
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Hello

Yesterday, I allready replaced all the tantalum capacitors in my Revox A77

Thank

Bye

Gaetan
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