JMP: wont power on...?

[cardinal]

So a '78 JMP 2204. Used it last night for the first in a few months. All good. Try to turn it on this morning and it just won't power up. No lamp light. Nothing to the tubes. Amp just does nothing.

Both fuses look ok, neither looks blown. And there was no "pop".

Tried various outlets. Tried different power cords (it's a UK market amp with a detectable cord).

So I'm guessing it's something internal to the amp? Any ideas?

 

[Jack Luminous]

Even if he fuses don't look blown, you have to test them with a multimeter to be sure.

 

[cardinal]

Even if he fuses don't look blown, you have to test them with a multimeter to be sure.

Both just checked fine with a multimeter.

 

[Jack Luminous]

If all fuses test OK and no voltage is getting to the valves, and worse , the on/off switch doesn't light up then the power tranny may be gone. You have to test the power tranny outputs by poking inside with one hand and the multimeter probe, having attached the other end of the multimeter to the chassis ground.

 

[glpg80]

Bad power switch.

I replaced both power and standby switches when I rebuilt my 74. The originals have contacts that will wear out and eventually no longer conduct.

 

[cardinal]

Yup. Bad switch. Happened to have a spare and now it's up and running again.

Thanks all! This place is awesome.

 

[cardinal]

This was the switch

Not looking to good

 

[glpg80]

So the left side is supposed to look like the right side. As you can see it was a complete mechanical failure in a way that nothing shorted to cause a fuse to blow. They just wear out.

 

[cardinal]

So the left side is supposed to look like the right side. As you can see it was a complete mechanical failure in a way that nothing shorted to cause a fuse to blow. They just wear out.

Yeah it literally fell apart when I opened it up.