Marshall jcm 2000 100 watt red channel light is dimly on when green channel is on

[Mikeguitar]

I have a 1997 Marshall jcm 2000 100 watt head,when on the clean green channel the red gain channel light is dimly on,but when switch to red channel is brighten up and green light will be completely off,seen another post like it but on a 50 watt

[Enzo]

If you saw the other similar thread, please read it closely and try all the testing we suggested there. Then come back herre with your results. The switching circuits should be the same.

[Mikeguitar]

So far I’m coming up with the same measurements and replaced a few things,but resistor r17 shows on schematic to be 100k ohms,I measured mine and it’s 47k?ill try to post pic of schematic too

[Mikeguitar]

Can’t figure out how to post pic of schematic

[TomCarlos]

Mike...

Which head do you have? I believe there are more than 1 version of the JMC 2000. Is it the TSL, DSL, etc?

https://www.thetubestore.com/marshall-schematics

[Mikeguitar]

Dsl 100

[TomCarlos]

Marshall JCM2000 100W DSL100 Schematic

[Mikeguitar]

That one you sent it’s 47,I had another one from somewhere and it said 100

[g1]

Then it sounds like this one would be the correct schematic for your amp, wouldn't it?
The 50W version in that other thread has a 100K there (R17 in switching circuit).

[Mikeguitar]

Yep looks like this is the one

[Mick Bailey]

Seems we have two threads for the same amp.....

Apart from the issue with LEDs, are all of the controls working correctly and is it sounding good on both channels? When you switch channels, do you get a thump and is the treble control scratchy?

[Mikeguitar]

No thump ,I’ll check the treble

[Mick Bailey]

The reason I ask Is I had one of these amps that had this issue. It also had the thump and very scratchy treble and it was down to severely leaking 470pf caps in the tone stack. I replaced these and the LED issue vanished.

[Helmholtz]

The reason I ask Is I had one of these amps that had this issue. It also had the thump and very scratchy treble and it was down to severely leaking 470pf caps in the tone stack. I replaced these and the LED issue vanished.

Just being curious: What was the type/technology of these 470pF caps? Do you know the brand?

[Mikeguitar]

Yeah a little scratchy,do you remember which board they were on?could you tell they were bad or did you have to test them? Thanks!