Mark III series Bass Combo low output

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Fictitiousfreedom
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Joined: Wed May 11, 2022 6:19 pm

Mark III series Bass Combo low output

Post by Fictitiousfreedom » Wed May 11, 2022 6:29 pm

I couldnt find the answer anywhere so sorry if its been discussed.
I have an old Mark III combo with a 15” speaker in it. The entire time I've had it it has a had a problem. After playing it for around 15 mins the output drops and the input and output gain need cranked really high to get a usable level. I usually stop playing it because i assume something is overheating. I took it apart today to see if there is an obvious component issue but everything looks fine. I have some experience with repairing gear but not the most. I make pedals and some pro audio stuff, ive even made a small SS guitar amp. I figured i would ask and see if there is a common problem like this or if one of you guys with experience could help me out. Thanks!!!!

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Enzo
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Location: Lansing, Michigan

Re: Mark III series Bass Combo low output

Post by Enzo » Thu May 12, 2022 7:08 pm

Amps with unstable output have been around as long as amps have been around.

If it were overheating, the rear panel would be very hot.

Gota photo of front and rear panels?

First suspects are any FX loop jacks, any insert jacks, and any preamp out and power amp in jacks. When the output drops, poke a plug into and out of each of those jacks a couple strokes. Any of them wake it up? Take your guitar or other test signal and plug into the power amp IN jack or the FX return. Does that come through? Or is that also still diminished?

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