JCM 2000 keeps popping HT fuse

[beasleybodyshop]

I have a 100 watt JCM2000 on my bench. I completely retubed the amp with known working tubes. I adjusted the bias and off she went. It came back a few weeks later with the owner saying it keeps popping HT fuses. I check bias again, seems ok. After an hour or so on my bench the fuse pops. Following the factory schematic, I can't find any shorts in the B+ supply....anyone dealt with this issue before?

[billyz]

Many of those jcm 2000 have conductive circuit boards that manifest as the amp heats up. CE sells the replacement board from Marshall. Or you can do a lot of Dremel work and rerun some resistors. I have also found some to have faulty ceramic caps that short intermittently. I just clip them out. Problem solved. Some even had the wrong value resistors loaded so check them . If I remember it's the grid resistors and even the grid load/bias feed resistors.
One more thing is the output jacks , the shorting lug is daisy chained and fails , especially when using the 8 ohm out. I run a hard ground wire across them all. I have seen several melted and arc'd over.

[bluesfreak]

billyz probably nailed it, JCM2000 (TSL/DSL) until late 2003 do have issues with the Main PCB getting conductive and resistors drifting when heating up, you need a new Main PCB to fix that properly... I recall tubesandmore do sell that...

[Stevem]

When you say "after an hour on the bench" is this at idle or under load?
Does the bias voltage change after 1/2 hour on the bench under load?
Any signs of arcing in the output sockets when viewed close?

[beasleybodyshop]

Thanks guys, I tried to talk the customer into ordering the replacement board, and he just told me to keep the amp He took all the new tubes back. I think im going to gut it and use the transformers and chassis for something.

[billyz]

Thanks guys, I tried to talk the customer into ordering the replacement board, and he just told me to keep the amp He took all the new tubes back. I think im going to gut it and use the transformers and chassis for something.

Sweet

You can fix it and sell it.