Output Seems To Lose Drive/Volume

[Neal Saenz]

With complete random timing, my MP2 output drops level like someone is instantly turning the drive down. It retains effects and such on the patch, but it loses that "oomph". It will eventually come back only to randomly lose it again. I can only assume this is a tube in its dying throes?

[Neal Saenz]

The voicing DOES seem to be affected slightly as well.

[MarshallJMP]

Do you loose gain or volume?

[rnolan]

Also is your power clean ? MP2s' (from my experience don't like flacky power)

[Neal Saenz]

Do you loose gain or volume?

It appears to be gain.

Also is your power clean ? MP2s' (from my experience don't like flacky power)

Visually everything looks fine onthe board. I don't see any signs or smell any indication that the power supply on the board is bad.

[rnolan]

So check the usual culprits (you probably have already), leads, jacks etc (clean etc). My gut feel is it's tube(s), how old are they ?? or could be tube sockets (this is sounding (a bit) similar to MikeBs MP1 issue). Do you use the CC master vol ? Otherwise it would seem to be be something failing/degrading after getting hot, more MJMP territory.

[MarshallJMP]

Mostly it's tube,so try replacing them first since this is also the easiest to do.

[Neal Saenz]

Apparently I am either not qualified to read a schematic or am simply looking at the wrong one: If I am looking down at the board with the front of the pre-amp facing away from my body, which jack is tube v1 and v2?

[MarshallJMP]

Then the left tube is V1

[Neal Saenz]

Changed out the tubes, same problem. Then I unplugged the cabinet to move things around and plugged it back in to the left output this time, and no issue. So I am only experiencing this issue when plugged in to the right 1/4" output.

[Systematic Chaos]

Did you check with the FX loop turned off?
I experienced something similar a couple of years ago and those issues were related to the CEM3381 ICs in the FX circuit.
Bummer....these ICs are obsolete. I managed to get some from Asia and also got a couple for MJMP....dunno if he still has some in stock....

If it´s not that, best bet would be somewhere in the Output-Mixer/Spkr-Sim/Output-Driver circuitry

Go check if the same happens when using the Spkr Sim outputs....

[MarshallJMP]

Could also be the volume pot,but SC has some good suggestions too.

[Neal Saenz]

Well, I've been playing it now for a few weeks through the left 1/4 " output with no problems at all regardless of which patch I use. Level and Room EQ knobs don't have any issues when dialing in/out. Going to take it apart in a week or so and see what i can track down starting with that 1/4" output jack.

[rnolan]

Check the CAB sim outs, if they both work then the issue is probably the output jack. If you check the signal flow schematic (page 2 MP2 manual) you can see that the stage outs peal off just before the cab emulator circuit. Also give the output level and room EQ  pots a clean (as that feeds both stage and cab sim outs and they are stereo pots (sometimes only one channel works)), Also check the FX sends, there should be signal there, but also check with loop out like SC suggested as this by passes the FX circuit (but the FX send should still get signal (make sure FX level switches (back panel) are switched to line level))

[Neal Saenz]

Thanks guys, will look into these over the next few weeks and check back here if I have any more questions. Might just sit back and get it completely overhauled in 2 months. Any idea what it would cost to have all the circuits cleaned up, re-soldered, etc to bring it back to factory new?