Blues Deluxe Reissue dead reverb

[jvm]

Blues Deluxe Reissue with no signal at output of reverb tank. I have subbed a working tank from another amp and still no return signal to amp. I can signal trace my audio signal to the tank input but have no audio at the tank output. I can, however, hear the springs crash through the return if I shake the tank. In testing components, I measure a dead short across R22(39k) Do I have a JFET problem? Q2(J113)Blues Deluxe Reissue.pdf

[g1]

Assuming the reverb pot is ok, you either have a bad Q2, or some fault telling Q2 to turn on when it should be off.
Check TP36, it should be around -15V for the reverb to be on.

[52 Bill]

Your post has some conflicting data. There is no signal coming from the output of the tank, but if you shake the tank you hear the springs rattle. You tried another tank, same results.

If the return circuit was turned off by the jfet or a shorted R22, there would be no spring rattle. I will assume that you read the short across R22 with the amp powered off and the reverb control turned down.

If the signal goes into the tank but doesn't come out, then there is a problem with the tank. Have you read the resistance across the transducer coils, specifically the input coil? The input coil is part of the feedback loop of the driver opamp, so the tank must have a high impedance input with a isolated ground jack. Did you check to see that the tank was plugged in correctly?

[Jazz P Bass]

I don't think that you will 'see' the reverb return at the tank itself.
The signal is a 'virtual earth' input to U2/ pin 5.

As TP22 indicates, test the opamp output.

I agree that R22 will read as shorted, with the amp turned off & the Reverb control fully off (CCW).
Or with Q2 shorted, no signal & Reverb control fully off.

[Enzo]

Pull the cable from the OUTPUT jack on the reverb pan, then touch it's tip with your fingertip. Make hum? If so, the return is working.As others said just above, if you get spring crash, the thing woks.


That aims me at a loss of drive. One thhing I don't see mentioned is the drive cable. Note it is shielded, but the shield is bit ground. Make sure there is good continuity between that shield and WJ2, and in fact on back to U2-2.

If that path is open, you still get signal at the hot pin of the pan jack, but no drive.

Oh, and you subbed a working tank, are all these tanks the proper type? The input side MUST be the non-grounded type.

[Enzo]

Pull the cable from the OUTPUT jack on the reverb pan, then touch it's tip with your fingertip. Make hum? If so, the return is working.As others said just above, if you get spring crash, the thing woks.


That aims me at a loss of drive. One thhing I don't see mentioned is the drive cable. Note it is shielded, but the shield is bit ground. Make sure there is good continuity between that shield and WJ2, and in fact on back to U2-2.

If that path is open, you still get signal at the hot pin of the pan jack, but no drive.

Oh, and you subbed a working tank, are all these tanks the proper type? The input side MUST be the non-grounded type.

[jvm]

My bad, guys. I HAVE signal t TP22. Apparently I won't "see" a signal at the tank output as Jazz stated. I also have -14V at TP36. I can touch the return wire tip with my finger and control the volume of the hum with the reverb pot so the pot is obviously ok.

[jvm]

I have checked to be sure I have the proper tank. I checked for continuity between the input shield and pin2-ok. I can signal trace all the way up to the pot side of R22. After R22, no signal.

[Jazz P Bass]

So maybe Q2 is toast.

With -15Vdc on the gate, the D-S pins should be in a high resistance state.
JFet's are normally low resistance until commanded otherwise (-15Vdc in this case.)

You could always remove Q2, simply to see if that clears things up.

[jvm]

Removed Q2. No change at all

[52 Bill]

Removed Q2. No change at all

I thought that you stated that you touch the return cable and can control the hum with the reverb control. Is this right or not?

If it is correct, then Q2 and R22 are not the problem.

[Jazz P Bass]

No change at all in what?

Is R22 still showing a dead short with the reverb control fully CW?

There are test parameters outlined on the schematic.
With a 4mv (man that's low) input signal, at 1K, you should see a 520mv signal at TP22.

Uhm. I just noticed TP21.
So you should see a signal at R35/46 connection.
467mv.

[Enzo]

Um, did we test the cable wires themselves?

[jvm]

Enzo, yes I did test the cables themselves. They are good. I broke a leg off of Q2 when removing it. I don't have another J113 on hand. Can I continue testing with it removed? I will just lose reverb footswitch function, correct?

[Jazz P Bass]

J113 either grounds the signal ( Reverb Off) or it doesn't.

So, yes, removing it will give reverb all of the time.