Carvin R600 intermittant protect trip

[Gtr_tech]

This thing is becoming a thorn in my side. It came in with the complaint of "cutting out". Indeed...after running it for a few mins, the prot relay dropped out and came back in within a few seconds. No DC at the outputs...very low offset in fact. While I was in there I noticed a few SMT lytics were bulged at the top. So I replaced them....*all* of them in the entire chassis. I figger'd if a few were gone/going, the rest weren't far behind. I ran it in the shop for a half hour or 45 mins....ran great. Called the owner (he's a regular....has been for years) and asked him if he cared if I gigged the thing for a night to make sure it was going to behave itself. No problem...take it out. It runs fine for the first half of the night, then starts back up with the intemittant protect relay dropouts. Offset at the outputs is normal as it was.

Carvin service has been worthless.....not returning my calls. Since this is a "when it feels like it" deal....its a real PITA to track down. Anyone seen this issue with the R600? I hate to charge this guy bench time for waiting for the problem to pop up, then repeating the process for the other 2 protect circuits.

[jrfrond]

Yeah, those intermittents are a real biotch!!! :O

At this point, I'd jump the relay contacts and put this thing on a load to see if you can make it do something stupid. You know, it COULD be something NOT related to the amp, e.g. relay drive circuit or the relay itself. It sounds like it might be thermally-related. Since the relay is always "on" during operation, perhaps the drive circuit is failing. I just looked at the schematic, and the protection circuit monitors DC offset, and also monitors bias on one power amp (points T1 and T2 opamp inputs are connected to either side of Q101, which is a transistor connected as a diode and replaces one diode in the bias diode string on what appears to be the left side power amp. So, you have a lot going on there.

[Gtr_tech]

I counted 3 seperate protect circuits. Thermal, overcurrent, and a pwr on timer (while not really a "protect" circuit, it can still cause the symptom when gone awry).

[MarkusBass]

Which version is it? There were many different versions and the one that I was fixing lately (Red Face) did not have any SMT components. Can you post a schematic? When I looked at the amp I thought about possible cooling problem. The amp had so poor cooling system that I think that it was one of the reasons why it was withdrown from the market. So I would check the quiescent current of the output transistors, their temperature and the voltage on the input (not output) of the thermal protection circuit. Of course, plug in a generator and a dummy load and give it some power.

Mark