1995 Marshall ValveState 8100U Amp - 60hz hum.

Rokinroller

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LEDS will light up proportional to loudness and gain applied . They dont light up under a light load .
Also just noticed in the pic above IC9 looks funky on right side . Almost like a melted line ?
Looks something V shaped like a jumper going across 2 resistors and the top of the letter M on the Marshall script on the board . Seems strange .
 
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SunfireSSR

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LEDS will light up proportional to loudness and gain applied . They dont light up under a light load .
Also just noticed in the pic above IC9 looks funky on right side . Almost like a melted line ?
Looks something V shaped like a jumper going across 2 resistors and the top of the letter M on the Marshall script on the board . Seems strange .
Thank You!!! I turned the gain up, they worked.
The IC9 and line is the glue they use to hold the Radial Caps in place. Just a stringer. Cleaned it off.
I put all the original caps back in since replacing them didn't fix anything. Tested out the same with hum. The Gain controls do affect that hum or amplify it.
 

Rokinroller

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Ok , so it sounds like the hum is coming from the pre amp section . What if you plug your guitar into the FX loop return jack ? Any hum then ?
 

SunfireSSR

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Ok , so it sounds like the hum is coming from the pre amp section . What if you plug your guitar into the FX loop return jack ? Any hum then ?
Hums regardless whether guitar is plugged in or not including the fx loop.

Another question...
The original footswitch is suppose to be a (P802).
I bought a Marshall footswitch (PEDL-91003) for it. Comes with LED's. Is it okay to use?
Because of the LED's and resistors they use to drop the voltage for the LED's, could this have caused the hum? The hum showed up later after I got the fs. Hums with or without the foot switch.
 

Ken Underwood

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This is a very simple one, you have said that you have turned down everything and it is still there, you have taken out the pre amp tubes, still there, so its coming from the output stage, so as others have said it must be generated from the power supply which means AC filter capacitors, just simple fault diagnosis, don't try and fix it your self get it to a good qualified Tech
 

SunfireSSR

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Well, the tech found the hum coming from the main power transformer. Anyone know where I can get one? I cand find the auto-transformer but not the power transformer.
Thanks in Adance..
 


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