Traynor YCV80 weak distorted channel

[Trevor G]

Traynor YCV80 started cutting out on the distorted channel to about half of the normal volume. Clean channel is fine.

I thought it might be preamp tubes so I replaced both of them. It didn't fix the problem so i tried swapping out the splitter tube, one at a time, with the two preamp tubes I replaced. That didn't fix it so I replaced all four power tubes. It did work for a day or two and then started doing it again, but now it never cuts back in. It stays at the low volume level. Clean channel still works fine.

I tried electrical contact cleaner on all buttons, pots, and tube sockets. I opened it up and looked over the circuit boards for burn marks or bad solder joints and thought maybe a couple looked bad on one of the tube sockets so I re-soldered them. Nothing has fixed the problem.

Does anyone know what could cause this?

[Chuck H]

Did you clean the contacts for the ribbon cables? Switching jacks? Anything could be responsible but it doesn't sound like a component failure at this time. More likely a bad connection. It could also be a bad solder contact but you should focus on anything you haven't deoxed and cleaned yet. Ribbon cables and switching jacks are the culprit so much of the time.

[Jon Snell]

If connections are clean, (pay attention to the relay contacts) and check out OK the next thing I would do is check the anode voltages on V1 & V2 then if wrong and a substitute valve makes no difference, R7 - R10 the anode load resistors on V1 & V2. The service manual states silly values. Use the nearest preferred value. Eg; 113k = 120k and 249k = 270k.
Computer generated values mean very little to a valve that has such a high tolerance, it is not a discrete medical grade op-amp after all. It's just a valve amplifier.