On Saturday, May 25, 2013 8:24:06 AM UTC-7, wrote:
Is there anyone here old enough to remember working on the Sony SL-2700 Betamax? I refurbish Beta's for resale and this one has a tough problem. The VCR works fine except for hifi audio - put in a hifi tape, and the hifi indicator lights but the sound is mute, both on the output and the VU LED's. The linear sound works fine if switched to that.

Tried swapping all boards related to audio, but got the same result, perhaps one of my substitute boards had the same problem.

Any ideas?

I spent most of last week working on a Sony DVW-A500 broadcast VTR machine replacing leaky (some VERY leaky - acid puddles) electrolytic caps. The bulk of the time was troubleshooting the 7 bad traces from acid destroying the copper on the (coincidentally) audio processor board.

Look for yellowish/brown 'mist' around the caps. By that time it's bad. EVERY cap I pulled had some leakage under it. A 'mist' an inch in diameter is likely to require re-constructive surgery. So far I've replaced around 100 caps in this machine, most just simply remove, clean the residue, replace and clean the flux. It gets more 'interesting' with 4 layer boards if it destroys the plated through hole. 2 layer boards are much easier.

FWIW I buy thousands of caps every year for my employer(s) and am called doctor capacitor on occasion.

G²