Marshall Haze 40 shorting out?

[Jazz P Bass]

Verify that the cap polarity is indeed correct.
If V2B pin 8 is getting a sloopy Vdc, that would explain the waveform on the cathode.

[ricach]

Verify that the cap polarity is indeed correct.
If V2B pin 8 is getting a sloopy Vdc, that would explain the waveform on the cathode.

Polarity is correct. I should mention that this issue with it howling can still be stopped (and started) with a stern fist to the chassis. This 'fix' usually only lasts a few seconds though.

[Jazz P Bass]

And you have resoldered the boards?

[ricach]

And you have resoldered the boards?

Resoldering the whole board was a daunting task so I hit most all components that were tied to a ground. I mentioned a stern fist, but a tap of a pencil on a component can also set it off. I've try to hit these components with a resolder as that occurs as well.

Although I have this nagging feeling since the beginning that it is bad solder joint(s) causing these problems, I'm hoping as these problem areas (like the bridge) surface, the replacing of components also involves resoldering of the area.

[g1]

Resoldering the whole board was a daunting task so I hit most all components that were tied to a ground.

Don't know how much time you have in it, but there will probably be a point where you will say "wish I had just resoldered the whole board".
You have pretty much proven to yourself it is a bad connection (responds to fist thump or board tapping). As much as we love to pinpoint the exact bad connection, sometimes it is just simpler (and less labour time) to resolder the whole board. Also if the board has several bad solder joints, there may be many more that are ready to go bad in the future. So it can also be preventative maintenance. Once you are in "resolder mode", what looks like a big job can actually go faster than you think.

[ricach]

As much as we love to pinpoint the exact bad connection, ......

Yup. Stubborn, stubborn, stubborn. But you bring up a good point and the thought of finally fixing the problem only to have another solder joint go bad in the near future does convince me that a complete resolder should be at the top of my list.

[ricach]

Amazingly the amp did still play fine with the sawtooth wave feeding the B+ rail, but only for a few seconds before it would blow the fuse. I replaced the diodes and we're back to a clean 300+ Volts and no fuses blowing. But now the howling can not be silenced by the Channel 2 volume pot. So the issue is not limited to the pre-amp, but elsewhere now. I should mention that while replacing the diodes I resoldered the power supply section and the Pre-amp section as much as I can see, but gave up doing the whole board for now. I wanted to assess the situation with the new diodes.

I need a new tip for my iron - the other is so wore out it was a real chore replacing those diodes along with the resoldering.