Hot Rod Deville III V1 reverb noise

[jvm]

Hot Rod Deville III with random popping/static at pin 1 of U2-A. I have replaced the op amp,, D30,R33, R34, and C14. No change whatsoever. I have tried freezing and heating all components associated with the circuit with no change. The ENZO knock test has no affect at all. No noise at pins 2 or 3. Anybody seen this before?

[soundguruman]

Hot Rod Deville III with random popping/static at pin 1 of U2-A. I have replaced the op amp,, D30,R33, R34, and C14. No change whatsoever. I have tried freezing and heating all components associated with the circuit with no change. The ENZO knock test has no affect at all. No noise at pins 2 or 3. Anybody seen this before?

because there's a broken wire inside the reverb tank? Because there's a bad reverb cable or RCA plug?

[jvm]

Reverb works fine and the noise is still there with the tank unhooked.

[Enzo]

Is the noise on the preamp out jack?

Plug a guitar into the power amp in jack and zero its volume knob. Still noise?

This noise ONLY affects the reverb drive? And with the reverb pan unplugged, you do not hear it through the speaker?

Does removing C13 stop the noise?

The signal to the drive input comes from a switching contact in the power amp in jack, if that were dirty it might do this.

You won't be able to measure signal at the input pins of the op amp, look up op amp inputs virtual ground.

[jvm]

Thanks, Enzo. The noise is present at the preamp out jack.
Guitar into power amp in with volume on 0, noise still present.
The noise is still there with the reverb tank unhooked at both ends.
Removing C13 does NOT stop the noise.
I cleaned the power amp in jack. No change

[Enzo]

I suspect your U1 is noisy.

[Jazz P Bass]

For those who may be playing along at home.
http://support.fender.com/schematics...atic_Rev-B.pdf

[jvm]

Thanks, Jazz P Bass, for posting the schematic. Enzo, I replaced U1 with no change. Still popping and frying eggs.

[Enzo]

OK, so isolate the problem.

Turning the reverb to zero - still noise?

Ground a clip wire and...

Upper right near preamp out jack is TP13. Ground it. Noise stop?

Now move down near power amp jack, TP18. Ground it - noise stop?

Upper left corner of power amp section, TP23. Ground it. Noise stop?


And while we are at it, look VERY closely at the solder on the pins of the power tubes. Any cracks?

[jvm]

Ok, Noise stops when grounding test point 23. I have re-soldered all tube sockets just to eliminate them as potential problems. Noise still there.

[Enzo]

And the other two?


And also when grounding TP18, ALSO have something plugged into the FX return.

[jvm]

Sorry for the incomplete data. Test point 13- no change, test point 18 grounded while jack inserted in power amp input- no change. Noise stops only when grounding test point 23.

[Enzo]

Alright then. Look at the schematic, TP13, TP18 have no effect, noise must be after them. TP23 kills it, so TP23 is after the noise source. TP13 or 18 is selected by contacts in the return jack, so a squirt of Deoxit into the jack and push a plug in and out a few times can't hurt. But assuming that doesn't work, narrow it down further.

Upper left power amp, find R40, R38. SHorting the bottom end of those - TP23 kills the noise. SO now ground the top end of each. Does either kill the noise? For that matter, instead of grounding the resistor, try shorting it end to end. Kill noise?


Another angle, is there ANY DC voltage on TP23. Instead of coming from or through R40, we could have a funky cap at either C28 or C24. C24 is a better suspect.


And we must not forget, Those lines run through a ribbon, so push on those and bend them a little to see if they are involved.

[jvm]

I replaced R40, R38, C24, and C28 since I had to pull the board. Noise popping and hissing still random. I can still stop it by shorting TP 23. Can the ribbon cable cause this type of random crackling?

[52 Bill]

Did you ever try changing the driver tube?