Marshall MG100HDFX low on volume

[Prairie Dawg]

Hello all, I'm a solid state noob although I've been repairing tube amps and vintage radio gear for a while.

I've got this Marshall MG100HDFX a guy wanted to see whether I could fix.

He said it had no volume-operated it without the speakers connected. It does have some volume but not nearly what it should. The clean channel has less volume than any of the gain channels.

It should be putting out enough volume to blow me out of my sneakers but it's just not there. I've been running it through a Celestion in one of my other amps that's down for repairs.

It was suggested on another site responding to a different poster that IC 4 may be on the Fritz. Does that sound likely to you?

Anyone have any ideas? Have you worked on these? Is there something I should look for? Is there a voltage map of these things?

Thanks for the help.

[J M Fahey]

Just to start with something, hook the preamp out of some other amplifier that you have into de power amp in or loop return and see if you can drive it into overload; it should blow you out of the room, or, more seriously, have enough volume to compete with or drown a drummer.
Drummers make excellent , "calibrated" sound pressure level references, and I'm not kidding.
If an amp can play along them, good; if not, it's a studio/bedroom proposition only.

[Prairie Dawg]

Just to start with something, hook the preamp out of some other amplifier that you have into de power amp in or loop return and see if you can drive it into overload; it should blow you out of the room, or, more seriously, have enough volume to compete with or drown a drummer.
Drummers make excellent , "calibrated" sound pressure level references, and I'm not kidding.
If an amp can play along them, good; if not, it's a studio/bedroom proposition only.

Good place to start. I'm a complete novice with ss amps but it's like working on PT-6s. It's not nice but it must be done and done competently.

Heck, if I learn something I might be able to figure out why my Baldwin D1 Professional quit on me in a fit of pique.