MP1 No Output, "Magic Smoke" smell

[Hambone]

Now that I've gotten a replacement guitar rig up and running, I finally have some time to try to figure out what's up with my MP1 and get it back up and running. Here's the scoop:

Last Saturday night, I was playing a show with my band - outdoors (under cover), mild night in the upper 60's F, low humidity - a great night to rock out! As we started our next-to-last song of the night, my rig just stopped making any noise at all. Tracing through, I found that it was the MP1 that had gone silent. The EQ light on the front left of the unit is lit solid no matter what patch is selected. The unit seems to behave as it should - it boots just fine and switches patches with no issues, there's just no output. I did notice the hot electronic "magic smoke" smell when it happened, but when I got it home and opened it up, I didn't find any evidence of any burnt devices, all the capacitors look great, and everything was seated snugly. Both tubes glow, and I didn't notice any obvious trace cracks anywhere under a magnifying glass...

I know the next step is tracing the signal path until I find the air gap, and my next step after posting this will be to have a look at the schematics. Are there any "likely suspects" that I should investigate first, or any thoughts on what the cause could be? Any help would be appreciated, as I have no intention of taking this bad boy out of service any time soon! :)

Edit to add: V1.38 firmware, Rev D main board, Rev F breakout board. Unit is stock except for a rear-panel input mod. Tubes aren't new but not ancient, somewhere around 6-8 years old, generic Sovtek units I think (can't see the label and don't want to stress the tube board to take them out unless/until I have to).

[rnolan]

Well that's not good  .  MJMP may have better suggestions but the EQ led going on solid makes me think something on the tube board as the EQ is straight after the gain stages and solid led means it's clipping.  It "may" be a tube  , that's obviously the easiest swap to try first.

[MarshallJMP]

So no sound at all? sometimes just the SS clean works which usually means a dead tube board. Now in your case with the solid EQ led I would start at U18 pin7, there should not be any dc there. Pin 7 is the output of the EQ section and also drives the EQ led (through D21,R119 etc..)

If you need some schematics or stuff like that you can always email me.

BTW do you have a scope?

[Dante]

Next band name: Magic Smoke Smell  ;D

[MarshallJMP]

Next band name: Magic Smoke Smell  ;D

;D

[Hambone]

Your question made me realize I don't use any patches on the SS channel, so I don't know if it makes any noise - I'll test that and get back to you. I don't currently have a scope or anyone to borrow one from. Would one of the cheap (~$100USD) handheld scopes on Amazon be adequate for the task?

[MarshallJMP]

Ok let me know. Those cheap ones are good enough. You just need it to trace some signals. You also need some sort of sinus generator, some of these scopes have one build in.

[Harley Hexxe]

Next band name: Magic Smoke Smell  ;D