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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 16th May 2020, 10:59 pm   #21
jamesperrett
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Join Date: May 2007
Location: Liss, Hampshire, UK.
Posts: 1,152
Default Re: Revox A77 issue

Quote:
Originally Posted by cgehansen View Post
Thanks Maurice. It was actually the input amp. I've swapped it for a good one and the pops have gone away. It was also affecting the left record level which sounded very scratchy as though the pot was dirty. Now it appears to be fault free
Sounds like DC running through the pot and switch which could be caused by a faulty coupling capacitor (C407?).

Last edited by jamesperrett; 16th May 2020 at 11:10 pm.
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Old 19th May 2020, 7:22 pm   #22
cgehansen
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Location: London, UK.
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Default Re: Revox A77 issue

Spot on thanks. C407 had shorted.
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Old 21st May 2020, 2:39 pm   #23
cgehansen
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Default Re: Revox A77 issue

Sadly the A77 appears to have a recording problem now. It plays fine and the input works. If I press the record buttons the vu meters work and then if I press play/record the red lights come on. However nothing is recorded on the tape. It does erase correctly though. This affects both channels. Iíve swapped the oscillator, rec relay card and checked all the wiring on the switch board and canít locate the fault. Is there something obvious to check that Iím missing?
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Old 21st May 2020, 8:42 pm   #24
cgehansen
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Default Re: Revox A77 issue

...oops sorry ignore the last post. It was a tape alignment issue. I've changed everything back to normal speed. The heads hadn't been moved so it was just a matter of swapping the capstan motor and removing the modifications on the pcbs.
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Old 21st May 2020, 11:39 pm   #25
TIMTAPE
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Default Re: Revox A77 issue

After such a mod or unmod the repro head should really be checked for the centring of the tape contact patch (left to right) on the head gap. You can't see it because the tape obscures it. Ideally the head is first relapped to remove the "flat" caused by previous tape wear. With the A77 these adjustments require removal of the control panel cover so you can see the head clearly. My trick to check the contact patch is to draw a patch of black with a whiteboard marker right on the head face, play a tape for a few seconds, remove tape and then inspect. The contact patch is of course where the black has been removed. The Revox single screw mounting allows for
minute rotation. It's a fiddly business but results in optimal contact and therefore response. The long term payoff is even wear and so long life on the expensive and these days harder to source heads.
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