marshall avt 150 overdrive problems

[Jimmyjoe]

I just bought a used avt 150. I got it home and I can get great sound from the clean channels and loads of volume. on the overdrive channels 1 and 2 I have a very LOW amount of volume, I do have the overdrive sound. any thoughts??? I have check voume knobs. tried different settings . any pointers out there?? man I should have tried all the channels other than the one he showed me!! lots of great info on here! thanks for your time.

[Enzo]

My first reaction is a bad op amp in the overdrive channel. But it could be SOOO many other things.

[Jimmyjoe]

thanks. is that a simple fix. or send it to the shop thing. no idea what that would cost to replace. any clue?

[Enzo]

That was just a hunch, but whatever it is, it will require changing parts on a printed circuit board. If you are not up to that, then it needs to go to the shop.

In my shop I'd guess your repair bill would be in the $65-80 range.

[Jimmyjoe]

Thanks enzo! I was playing it this morning to check for any changes....no luck . there is volume of a 4 coming out (1-10) scale with the master all the way up on the od channel. suppose i could use a pedal on the clean channel. I do like equipment to function properly. how would i find a good repair shop in des moines iowa? I would try bench work and soldering if need be...i use to be a mechanic. just afraid i would cost myself more in the long run. Thanks for your quick responses!!

[Enzo]

Des Moines is not a small town, I have to think there are competent repair shops in town. Music stores often have them, but ask local musicians who they use for service.

[Jimmyjoe]

right on Enzo.....I did that. here's the funny part. they could tell me places I should NOT take my amp. I just bought a used fender tonight...so I will be digging in on fixing this just for the experience. where should I start? I have ohmeters and a few different testers from my mechanic days.

[Enzo]

You need to get at the preamp board - the one with the controls - and follow the schematic. Check the output pins of each op amp IC looking for DC offset voltage. Not concerned over a fraction of a volt, it will be obvious most times, as in several volts.