Princeton 65 SS Intermittent Buzz

[Perkinsman]

When the unit warms up, the Volume & Reverb independently increase/decrease the level of buzz. The Volume knob sounds like more of a hum. The Reverb knob sounds more like a buzz. When I turn down the Volume & turn up the Reverb knob, the buzz seems more pronounced. If I turn the Reverb down & the Volume up, the hum becomes more pronounced.
schems.com/bmampscom/fender/Princeton_65.pdf

[Perkinsman]

Anyone?

[g1]

Have you checked the power supplies for proper voltages or any excess ripple?

[Perkinsman]

All DC voltages are very close to the schematic. I have a scope but I don’t know which points to test for excessive ripple or what would be considered excessive. Could you please tell me what points to test? Btw, the amp only makes noise when a cable is plugged in.

[The Dude]

If it only makes noise when a cable is plugged in, check solder connections on the input jack.

[Perkinsman]

Two input jacks & buzzes in both so I doubt that’s it but I’ll resolder just in case.
edit: resoldering inputs didn’t work, still buzzing like a cheap TV

[Jazz P Bass]

Does the noise change if you turn the guitar volume to zero?

[Perkinsman]

Yes, see post #1 for details

[g1]

still buzzing like a cheap TV

The reverb or the volume? You will need to specify at all times. I'd suggest leaving the reverb off (turned down) til you sort out the main hum.
You said it was intermittent, can you physically make it cut in and out?

[Perkinsman]

I’m not sure what more I can describe than I already have in post# 1. BOTH volume & reverb will independently act like a volume control for this noise, lowering down to no noise.
As far as being intermittent, I initially thought it only made the noise when it warmed up but the more I turn it on & off, it appears to be occur all the time.

[Perkinsman]

Bump

[Perkinsman]

I had to walk away from this amp for awhile. It has a buzz I need help solving.

[DrGonz78]

Have you checked pin 7 on U6B? My thought is that those IC’s can create some noise. With all controls down measure pin 7 with a voltmeter. I would measure all voltages on U6. Scoping the signal through the amp could tell us where the noise is and hopefully where it is not.

[Perkinsman]

Thanks for assisting. Do I need to inject an AC signal into the input jack? With no ac signal, all controls at 0, all msmts in Mvac:
U6b
Pin 1= 106
pin 2= 3
pin 3= 210
Pin 4=.6
pin 5= .2
pin 6=1.69
pin 7= 1.7
pin 8= 1.7

[DrGonz78]

I would inject signal if I was looking for noise using a scope. I would look through the whole signal path up to that point to locate where the noise was present. I don't think there should be 1.97vac at pin 7 but I could be wrong, perhaps the meter is confused too. What is the DC volts on all the pins of U6?