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JTM30 Problem -- Please Help!

3/12/2000 7:42 PM
neddyboy	JTM30 Problem -- Please Help! My JTM 312 started fading out, going from full volume to a faint, scratchy level after it had been on for about 5 minutes. Sometimes if I really attacked the strings it would pop back to full volume, but fade again. I'm not much of a tech. Most of my electronics experience is at the level of rewiring guitars, building foot switches, or fixing guitar cables. I first checked the tubes -- all OK. I pulled and checked all the caps (only with a multitester, not for capacitance) -- all OK. I put all the caps back in and now I get nothing, no sound at all, not even hiss. My more-experienced brother-in-law and I went through the board and traced the signal. I'm getting signal at the emulator-out jack and all the power circuits are working, but the signal's not making it to the power section. So, with that background, I have two questions about the problem. Is there anything obvious that could have caused the first problem, ie the fading out? Could whatever caused the fade-out problem failed entirely and caused the break between the preamp and the power amp? I also have one more question about resources. I found a schematic, but I'd also like to find a service manual. Anyone know where to look online?

3/12/2000 7:42 PM

neddyboy

JTM30 Problem -- Please Help!

My JTM 312 started fading out, going from full volume to a faint, scratchy level after it had been on for about 5 minutes. Sometimes if I really attacked the strings it would pop back to full volume, but fade again. I'm not much of a tech. Most of my electronics experience is at the level of rewiring guitars, building foot switches, or fixing guitar cables.

I first checked the tubes -- all OK. I pulled and checked all the caps (only with a multitester, not for capacitance) -- all OK. I put all the caps back in and now I get nothing, no sound at all, not even hiss.

My more-experienced brother-in-law and I went through the board and traced the signal. I'm getting signal at the emulator-out jack and all the power circuits are working, but the signal's not making it to the power section.

So, with that background, I have two questions about the problem. Is there anything obvious that could have caused the first problem, ie the fading out? Could whatever caused the fade-out problem failed entirely and caused the break between the preamp and the power amp?

I also have one more question about resources. I found a schematic, but I'd also like to find a service manual. Anyone know where to look online?

Replies:

Andy HiMaybe too simple,... -- 3/12/2000 10:55 PM