Need Help with Marshall Mosfet

[sasnak007]

I recently came to own a Marshall Mosfet Lead 100 head (model 3210) that doesn't really work, and I'm looking for any assistance I can get.

Basically, when I plug in the amp just hums. If I crank up the master volume, I can hear the guitar very faintly. If I move the springs in the reverb unit, the sound comes through the speakers loud and clear. Also, if I plug into the effects loop return jack, I can hear the guitar fine (just can't use any of the controls and whatnot).

I went over all of the solder joints, and verified the +/- 15 and 34 voltages at the ICs. I noticed that I get TONS of hum if I switch the reverb on or if I touch the treble control.

It's got to be something in the preamp, right? I'm not real experienced electronics, but I know enough to get myself into trouble

Sorry to rant, but I'm really in need of some help from someone with a little (or a lot) more experience with amp repair than me. Please, if you have any suggestions or might be able to help me at all, I would really appreciate it.

Thanks!

[Gtr_tech]

The CA3046 IC caused problems in those. I just had one come through here recently that had issues with funky ch switching and a *real* weak sounding OD channel. Replacing that IC resolved it.

[Enzo]

The 3046 is a good call, and i would also go down the op amps and check pins 1 and 7 for unwanted DC offset. (Indicating a bad IC usually)

[sasnak007]

Hey thanks for the replies!

I went ahead and ordered a replacement for the CA3046.

Also, pin 1 of IC1 was reading 15 volts. I don't if it's supposed to have voltage or not, so I went ahead and ordered a replacement.