Marshall 6101 (combo) problem

siav

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Hello,

I haven't played with that amp for a while and I have a problem with it.
No sound at all... Everything is lighting up as they should, the fuses are ok.
I have tested the speaker (Celestion gold, 8 Ohm) with an other amp and it works properly.

Could you please suggest a test runthrough or a diagnostic plan?

Thanks a lot!
 

fitz288

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Hello,

I haven't played with that amp for a while and I have a problem with it.
No sound at all... Everything is lighting up as they should, the fuses are ok.
I have tested the speaker (Celestion gold, 8 Ohm) with an other amp and it works properly.

Could you please suggest a test runthrough or a diagnostic plan?

Thanks a lot!
Tubes can light up and not function correctly.
Try a new 12AX7/ECC83 in each position to see if it's just a tube.
Hope it's not the dreaded EEPROM chip failure (I have a spare).
Pete ( @anitoli ) is the 6100 guru, but I don't recall him posting recently.
You could try contacting him through his web site:
 

Jon Snell

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If the speaker is completely quiet, check the speaker is plugged into the correct output socket and the effects loop is switched out or looped through with a jack lead to remove that from the equation.
I wouldn't swop valves yet as confusion may set in.
 

siav

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I tried plugging the speaker to both output sockets (turned off the amp in between, of course), also used a jack to close the effects loop: none helped
 

siav

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There is a little hum but nothing comparing to the hum when the amp is working properly.
 

fitz288

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I wouldn't swop valves yet as confusion may set in.
I'm not sure what's confusing about swapping tubes to check for a bad tube issue, unless you're having problems walking down stairs or eating with a fork.
That would be the first thing I would try.
There are not a lot of easily serviceable parts to the 6101, so if it's not a simple tube issue, you may want to find a good local service tech.
 

siav

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I got some sound now after using electronic cleaning spray to clean the jack I put in the effect loop.
I only get sound (normal) from the lead channel. The volume pot of the crunch channel makes a terrible crush sound when I touch it and no sound from channel 2.
Clean channel is silent, no sound.
 

fitz288

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I got some sound now after using electronic cleaning spray to clean the jack I put in the effect loop.
I only get sound (normal) from the lead channel. The volume pot of the crunch channel makes a terrible crush sound when I touch it and no sound from channel 2.
Clean channel is silent, no sound.
V1 is clean channel only, might be part of the problem.
V2 & V6 are channel 2 - V2 is also shared with channel 3.
All new tubes on these rigs can cost a boatload so see if you can get away with just one or two new ones.
1651760470151.png
Also try some cleaner in the pots.
Be sure to use a lubricating cleaner like Deoxit.
A straight cleaner can remove the pot lubricant and lead to pot failure.

Good luck!
 

siav

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Thanks guys!

The problem is/was channel 2 volume pot. It's not as smooth as the other ones and it seems faulty....
 

fitz288

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My problem is now how to fix that volume pot??
Not sure what your electrical skill may be.
Do you have a local electronics repair shop nearby?
Your location link says you're on an island off the coast of Norway?
 

siav

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I have good skills but I have to see what someone is refering to.
Electronic repair shops arent very common here in Norway and if they exist, it cost a liver....
 

siav

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Ok so I cleaned up the CH2 volume pot successfully with a proper electronic contact cleaner, tested while the amp was out and laying up in the chassis, everything was ok.

After putting back the amp inside the chassins, again, no sound from any channel!
I tried putting a cable to close the FX loop and connected the HP jack to an other output (turned off/on the amp in between of course!) and still nothing...

Any help to diagnose the problem please?
 

fitz288

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Ok so I cleaned up the CH2 volume pot successfully with a proper electronic contact cleaner, tested while the amp was out and laying up in the chassis, everything was ok.

After putting back the amp inside the chassins, again, no sound from any channel!
I tried putting a cable to close the FX loop and connected the HP jack to an other output (turned off/on the amp in between of course!) and still nothing...

Any help to diagnose the problem please?
Heeelp please...
Just to clarify.
Everything was working with the chassis out, but nothing when you put it back in the combo?
Have you repeated this result?
Are there other variables like, did you use a different speaker or speaker cable with the chassis out?
 

siav

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The amp turns on, the tubes lights on too, the only variable is that it was out of the chassis and then in again.
 

fitz288

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tested while the amp was out and laying up in the chassis, everything was ok.
The amp turns on, the tubes lights on too, the only variable is that it was out of the chassis and then in again.
Chassis out, plug in a speaker and guitar - sounds awesome? or just lights up "everything ok"?
It's hard to tell from your responses what is working and what is not working.
You changed a few tubes, and then it was a volume pot cleaning.
These are complex amps that sometimes require more knowledge than I have.
If the simple fixes are not working (tubes, jacks, etc.), I'm not sure how much I can help.
But I'm trying to get a clear idea of your amp's status so someone smarter than me (@anitoli ?) will have a place to start asking more questions.
 

siav

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Sorry... when the chassis was out, plugged in HP and guitar > sounds like a good amp.
When I put the chassis back in, with HP and guitar plugged, I get no sound (but everything lights up).
I haven't changed any tubes, just used electronic contact cleaner to fix the CH2 volume pot (which was fixed when I tested with the chassis out).
 

fitz288

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when the chassis was out, plugged in HP and guitar > sounds like a good amp.
When I put the chassis back in, with HP and guitar plugged, I get no sound (but everything lights up).
Repeat the process.
I can't think of a reason it would work outside of the combo, and not work when put back.
Pull the chassis and look for something that may have been knocked lose when you put it back in.
 

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