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Marshall JMP production yr. 1979 Amp Trouble

5/24/2000 10:02 PM
Marshall JMP production yr. 1979 Amp Trouble
The amp is not blowing fuses, no funny smell,  
the amp comes up but has what sounds like a  
grounding problem, any comments could help.  
All tubes are less than one yr. old and are  
in perfect working order. Ive got a gig  
this weekend and this baby has to be ready  
to use. What is the problem?
5/24/2000 10:08 PM

"the amp comes up but has what sounds like a  
grounding problem. What is the problem?"
Maybe it's a grounding problem.
5/24/2000 10:12 PM

Seriously though. There's no way anyone could diagnose the amp with this little bit of information. Start by checking all your ground points. Also, how do you know for sure all your tubes are in perfect working order?
5/27/2000 10:41 AM
Richie {~}==:::
A few things in these amps that go bad i see alot  
are the input jacks and loose or cold solder joints.  
But as Tonefactor said hard to say by guessing.  
just a couple things to look at.  
5/31/2000 1:34 AM
Mike SHaw
Might want to check your pots too. See if they make funny noises when you turn them. Mike
6/8/2000 4:10 PM

The workmanship in this era of Marshall's varyed from bad to worse. I remember fixing intermittant fuse blowing problems in one 100 Watt combo, that had no solder on the power tube connections ! The amp actually worked fine and then popped fuses when it felt like. The connections were properly wrapped around each tube pin, and just never soldered at the factory !
6/8/2000 5:57 PM
Now that I think about it, my stand-by switch was intermittant. Cold solder joint. Mike
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