JCM800 2203 late 80s - background crackle noise

[Greg_L]

Are you saying you only see the spikes if your scope is not grounded via it's ground clip?
Is the amp plugged into the same outlet as the scope?

The ground clip is always grounded.

I'm saying that I'm seeing the noise spikes anywhere I probe in the amp. If I ground the probe clip to the probe tip itself there is no noise, so it's not the probe or a ground clip loop antenna effect picking up noise. The same tests on other amps in the same room does not have this result.
I've cleaned and tightened and checked every power/signal ground in the amp.

And yes the amp and scope are on the same outlet.

[Greg_L]

Ok I lifted the OT primary CT.....still spiky crackly noise in the B+

So next I guess I'll bypass the choke. What value resistor should I put in it's place?

[Helmholtz]

So next I guess I'll bypass the choke. What value resistor should I put in it's place?

For the test just jump it with a wire.

[Greg_L]

For the test just jump it with a wire.

Ok so like it's not even there.

[Greg_L]

Ok I'm sending this thing away. I give up. Nothing I'm doing fixes it nor am I finding the smoking gun.

I lost this one.

[nosaj]

Did you scope the pt with leads disconnected?
nosaj

[J M Fahey]

Good for your mental health

[Greg_L]

Did you scope the pt with leads disconnected?
nosaj

I did and I got slightly different readings on each half of the secondary, but I did not see the noise spikes.

[Greg_L]

Um, well, to add to the madness......the amp is quiet now.

[nosaj]

Um, well, to add to the madness......the amp is quiet now.

Have you tried to plug it in?


nosaj

[nosaj]

Maybe you fixed a bad connection lifting leads and resoldering them.
nosaj

[Greg_L]

Maybe you fixed a bad connection lifting leads and resoldering them.
nosaj

That's gotta be it. I did a lot of fudging around in the power supply this afternoon. A hollow victory, but a victory nonetheless....for now.

[Greg_L]

Update:

Amp got used hard tonight. Worked great, flawlessly, not a hiss, pop noise, or crackle to be heard. Go figure.

[nosaj]

Just goes to show when your ready to throw in the towel , How close you might be to actually winning. Good Job.
nosaj