Mesa Studio .22 plus loud hum

[Randall]

Amp shows up dead, won't power up. Power switch is dead, so I replace it.

Now it has a loud hum, and won't pass signal. The noise follows Vol pot and is almost quiet if Volume is turned off, but there is still a little of the same noise if Master is cranked. It is completly quiet if Vol is up and Master is down. Pulling V1 has no effect. Pulling V2 silences the Vol related noise, but the wee bit on the Master still remains.

If I engage the footswitch, it passes signal to some extent, not nearly loud enough, but the noise remains.

Not sure I am understanding these LDRs in this circuit. Not seeing signal on V1. With footswitch engaged, what I see on V2 is bizarre. The first plate replicates the sine, but there is two of them. They start on the left at the same point, and then one rises and one falls. The second plate also replicates the sine, but it there are multiple wiggly traces of it.

Does anyone want to chime in on this? Frankly, I am scratching my head over here. How I dread working on these Mesas.

[The Dude]

At the risk of sounding like Mr. Obvious, have you tried changing V2?

[Randall]

Swapping V2 effects no change.

[The Dude]

Check filter cap(s) on the node that supplies V2 plate.

[Randall]

Tacking in a 33uF across all three filter caps effects no change.

[g1]

As far as the scope waveforms, it sounds kind of like a triggering issue. Has anything been changed on the trigger settings?

[Randall]

I really don't think it's the scope. I have been using it for 30+ years.

[Dave H]

As far as the scope waveforms, it sounds kind of like a triggering issue. Has anything been changed on the trigger settings?

Perhaps the triggering issue and hum are because something isn't grounded near the input before the vol pot?

[Jazz P Bass]

The first post schematic link is dead.

[Randall]

Really? I was able to download it just now.

[Dave H]

It doesn't work for me. I get the dreaded single pixel.

[Enzo]

Randall, you uploaded the file, but it was one already in the system pre-crash. Usually the uploader can open it because the file is still in your cache. No one else can open it. I get 1x1 pixel as well.

[Randall]

I shall try to post it again here.

[vintagekiki]

I shall try to post it again here.

Nothing to show (clear.gif 1x1 pixels)

[Jazz P Bass]

Is the schematic that I posted in Post #9 incorrect?

Note: I 'zip' files from the crash, that way they are accepted.