|
Vintage Tape (Audio), Cassette, Wire and Magnetic Disc Recorders and Players Open-reel tape recorders, cassette recorders, 8-track players etc. |
|
Thread Tools |
16th May 2020, 10:59 pm | #21 |
Octode
Join Date: May 2007
Location: Liss, Hampshire, UK.
Posts: 1,870
|
Re: Revox A77 issue
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. |
19th May 2020, 7:22 pm | #22 |
Pentode
Join Date: Sep 2017
Location: London, UK.
Posts: 115
|
Re: Revox A77 issue
Spot on thanks. C407 had shorted.
|
21st May 2020, 2:39 pm | #23 |
Pentode
Join Date: Sep 2017
Location: London, UK.
Posts: 115
|
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. I’ve swapped the oscillator, rec relay card and checked all the wiring on the switch board and can’t locate the fault. Is there something obvious to check that I’m missing?
|
21st May 2020, 8:42 pm | #24 |
Pentode
Join Date: Sep 2017
Location: London, UK.
Posts: 115
|
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.
|
21st May 2020, 11:39 pm | #25 |
Octode
Join Date: Jul 2006
Location: Perth, Western Australia
Posts: 1,965
|
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. |