No sound on select preset channels and weird output level knob behavior

[Andrew Smith]

ADA MP1 doing some weird things
Played an MP1s for years in my rack rig but not done much repair as the only thing I've ever blow is a fuse. Just received my second MP1 (v1.38) and it has a few weird problems. So far 2 that stand out.

1)   On certain preset channels, the output is non-existent. It seems a bit weird because channels 1 and 2 I get no sound, but 3-4 I get sound, then 5 and 6 no sound, and on it goes in pairs. It doesn't matter what voicing I put the channel on, I get nothing. (tested using the headphone out and the Out A and B using my Torpedo direct box)

2)   The output is very low coming out of Out A and B until the output Level knob on the front is up near 4 o'clock where it suddenly springs to life for some reason... happens on all the channels with a signal.

Kind of weird. I've never had a problem like this with an MP1 before aside from replacing the battery or a tube. The input jack works fine I can get all the peak lights to light with the settings you would expect to peak each section of the pre.

Any suggestions would be really helpful :)

[MarshallJMP]

When you change voicing the master volume is set to zero, did you check the master volume (not the front vol knob!!)

2 could either a bad pot or a bad cap.

[Andrew Smith]

Aha well you've solved the mystery of the beginning channels, so thanks... masters were on 0  :facepalm:

seems channels 70-110 and 112-115 are still being weird, but I only need a couple of banks so all Good :D


As to the Output Level pot. I think it might be dodgy because the unit now only operates when it is full up.

I'll open it up on the weekend and take a look

Thanks :D