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Vintage Tape (Audio), Cassette, Wire and Magnetic Disc Recorders and Players Open-reel tape recorders, cassette recorders, 8-track players etc.

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Old 21st Jun 2021, 5:35 pm   #1
bockhanal
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Default Revox A77 Fast Forward failure

Hello.
I'm working on an A77 Mk III which has been in a cupboard for the last 23 years. Play, Record and Rewind now work as they should but Fast Forward does not work at all. I replaced all the capacitors on the motor drive board and cleaned the relay contacts. Relay C for Fast Forward actuates and holds when the push button is operated. AC voltages for the right hand reel motor are shown in the service manual as Play - 55; Fast Forward - 105; Rewind - 15. The corresponding voltages I'm measuring are 73, 24 and 6. The AC feeds to the board measure OK. I'd be really grateful for any suggestions as to what could be causing the problem.
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Old 21st Jun 2021, 6:14 pm   #2
ms660
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Default Re: Revox A77 Fast Forward failure

Were those voltages measured at the transformer with respect to the 0v connection?

Lawrence.
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Old 22nd Jun 2021, 2:00 am   #3
TIMTAPE
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Default Re: Revox A77 Fast Forward failure

With brakes off and the reel motor button in are both reel platters equally easy to turn by hand?
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Old 22nd Jun 2021, 9:15 am   #4
lesmw0sec
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Default Re: Revox A77 Fast Forward failure

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Originally Posted by TIMTAPE View Post
With brakes off and the reel motor button in are both reel platters equally easy to turn by hand?
A good point. It is quite common for a machine unused for some time to have the brakes stuck to the drum.
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Old 22nd Jun 2021, 8:09 pm   #5
bockhanal
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Default Re: Revox A77 Fast Forward failure

Thanks for the responses. Platters turn freely, no binding. I checked that I was using the correct terminals to measure voltages and found a fault. I had replaced a couple of components on the capstan speed control board and when I reinstalled it I managed to reverse the connections from the 130 volt winding on the transformer. Sorted that and Fast Forward is restored. Spot the muppet. Thanks again for the input.
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Old 22nd Jun 2021, 9:22 pm   #6
TIMTAPE
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Default Re: Revox A77 Fast Forward failure

Glad you found the fault. I had read you saying the fault had developed while sitting idle for 23 years, rather than the work you subsequently did on it.
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Old 22nd Jun 2021, 11:22 pm   #7
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Default Re: Revox A77 Fast Forward failure

If making the error made you a muppet, then finding and correcting it moved you further in the unmuppet direction than the error moved you muppetwards in the first place. The reason for the difference is that you now have the benefit of experience you would not have gained otherwise!

Everyone makes mistakes. What separates the good guys and the bad guys is what they do afterwards.

David
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Old 22nd Jun 2021, 11:42 pm   #8
TIMTAPE
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Default Re: Revox A77 Fast Forward failure

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Originally Posted by Radio Wrangler View Post

...Everyone makes mistakes. What separates the good guys and the bad guys is what they do afterwards.
Well said David. Congrats to the OP for having retraced steps and discovered the problem.
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Old 23rd Jun 2021, 10:02 am   #9
ms660
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Default Re: Revox A77 Fast Forward failure

I thought it might be that, the voltages measured were more or less the same as some of the voltage differences between the transformer taps.

Lawrence.
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