Studer A807 recording only on 1 channel

C

carlosraj

New member
Hi

Earlier I had a problem of unable to record at 15ips with this recorder. I rectified the problem with the guidance from the forum. The problem was the bias setting was at zero for 15ips. After that it was recording OK all this while until recently. Now when I record, both channel start recording OK, but after a few minutes, the left channel stops recording totally. While recording, I usually switch to "repro" to monitor the present recording. Both channels are reproducing the current recording at the beginning but after a few minutes the left channel is suddenly playing back the previous recording( i.e it is not erasing the previous material and also not recording the present material). The right channel is doing fine. Can someone familiar with this problem give me some guidance.

Thanks

Carlos
 
On most versions of the channel card, there is a relay that controls both the erase and record head for that channel. If that relay switches state unexpectedly, you will get the problem you're describing. Off the top of my head I can see three possibilities:
1. The K1 relay has gone bad.
2. Something has gone wrong with the transistor pair (Q7/Q8) that drive the relay.
3. The control line C-RECX is changing state abnormally - this is the Really Bad option, because it could be anything up to and including software.

K1 is the relay under the metal shield unfortunately, which is a pain in the arse to get off as the power transistors are attached to it. You can probably pop off the little retaining clips with a screwdriver if necessary, but don't let them escape.

What I might try first is to physically swap the cards over. This is a bit of a nuisance owing to the many flying connectors carrying the audio across the top. It might be a good idea to use a pen down the side of them, so that you have a mark on both the top and bottom of each plug and you can get them back together. They are all labelled, but the labels may fall off owing to the extreme age of the glue.
If the problem moves from one channel to the other, it's definitely on the card itself, rather than option 3 (the data line going bad).

If you've never removed the cards before, note the bolts at the top of each one. These are to allow you to lever the cards out, by putting a screwdriver or similar implement in below each one and pushing down on the handle, ideally both sides at the same time. The latches at the bottom of the card cage allow the tray to slide out providing easy access.
When putting the card back, make sure that the card falls into the guide slots properly, and that the pins line up with the sockets as the cards may flex a bit.

If the problem is definitely the card, I would try replacing (or getting someone else to replace) the K1 relay first as it's a mechanical component. Otherwise you'll need someone more adept than me at debugging and testing transistor circuits to help you out.
 
Since the problem is intermittant is the connector P2-19 (cntrl to Q7) fairly accessable? If so hook a meter on it on longish leads and check the voltage when the fault occurs.

If the voltage does not change with the fault, the problem is on the board.

On a general theme I would have loved (I think?) to have worked on these machines and due to their complexity and access problems would have developed various "sniffers" to hang in them based on Jfet op amps and LEDs.

Dave.
 
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