Fender Stage 100 No Reverb Need Help?

[Jam]

I have a stage 100 and I have no reverb I swicth the reverb pan with another one and it still dont work. I dont know where to to start. Thanks

[Enzo]

Start by isolating the problem.

Does everything else work?

There are two reverb circuits, the drive circuit, and the return or recovery circuit.

There are two cables plugged into the reverb pan. Have you tried swapping them? But assuming they were right, turn the amp on and turn the reverb up halfway. Now rock the amp back and forth enough to crash the reverb springs. ANy sound from it?

Pull the two cables out of the pan. Touch the tip of each one with a finger. WOn;t hurt you or it. The one from the pan INPUT jack SHOULD make a good hum when you touch it. If it does, then the return circuit works, and if it makes no sound, then the return circuit has the problem.

U4 is the reverb IC, and handles both drive and recovery. A bad one means no reverb.

[Jam]

stage 100

Thanks for the help.Everything else works. The white tip that goes to the out on the reverb tank I get a hum but the red tip that goes to the in on the tank I get nothing? Thanks

[Enzo]

OK, so the recvoery works, and your drive side has issues. If the cables have continuity with where they go on either end, then a bad IC is likely.

[Jam]

stage 100

Thanks, So you mean I need to replace U4 IC ? What do these IC do? Thanks

[Enzo]

From way out here, all i can say is, likely.

The ICs are op amps, they are functional blocks that amplify.

[Jam]

Still dont work

I replace U4 IC and it still dont work what would be the next step? Thanks for your help

[Enzo]

I'd be using my scope. I am guessing you don;t have one?

With the amp on and the reverb up, does shaking the reverb pan make the loud spring crash noise?

The drive cable and return cable are shielded wires. The return cable has the shield grounded, but the drive cable shield is NOT grounded. Verify that. And verify the cables. FLip over the reverb pan, and expose the amp board - power off. Firstm just to be sure, pull the cables out of the reverb pan jacks and measure resistance across each pan jack. One will read really low and the other maybe 150-200 ohms. It will either be open or it will be correct. Is either end open? Of OK, plug them back in. Now check continuity from the shield contact of the drive jack on the board to the shield side of the INPUT jack on the pan. Likewise, check continuity from U4 pin 1 to the hot pin of the pan jack. We are testing to see that the cable itself is complete.

With the amp running and reverb up, set your meter to ohms, ground the black probe, and touch the red probe to pin 3 of U4. That should send a pop through the reverb. DO you get a reverberated pop from the speaker?

[Jam]

stage

Ok I was go down the list of what you said to try and I was having issue with the red RCA cable to the pan so i got my cable tester and it the red side was shorting out. So the first thing I was going to do is replace the cable. Where do I get a cable at? does any RCA cable work? Thanks

[Enzo]

Plain old vanilla RCA patch cord.

[Jam]

I replaced the cable and it works and it dont sound right and it hums real loud but the hum goes a way when you turn the reverb all the way down? Any info will be helpful Thanks

[Enzo]

Pull the cables off the reverb pan. Turn the amp on and the reverb part way up. Now touch the tip of each reverb cable plug with your finger. One should make hum come out the speaker. THAT one should plug into the OUTPUT jack on the reverb pan. Make sure.

Pull the reverb pan out and with it disconnected, measure resistance across each jack. One should measure very low resistance and the other maube 100-200 ohms. What we don;t want to see if one end being open circuit. The things will either be open or they will be correct.

And are you sure the new cable is OK?

[jmaf]

Isn't there something about not hooking up the in and out grounds together? Maybe he has a ground loop.

[Enzo]

Not quite.

On the drive end, the shield side of the cable is not grounded. It goes to the invert pin on the drive op amp, with an RC to ground. So that shouldn;t be grounded at all, let alone to the return side. However, I wouldn;t offhand expect hum from that. MAybe. I would expect any such hum to be reverberant.

And since this is RCA cables on both the pan and the amp ends, you can't wire it wrong, ground wise.

But that does bring up having the right reverb pan. Pans are not all the same, so just sticking a different one in there doesn't mean it is the right kind.

What is the number on the reverb pan you are using?

If you are not familiar with that, look for a number that resembles 4EB2C1B on the reverb thing.

[jmaf]

I had a pesky case of hum in a reverb tank here once, I remembered that ground loop issue, though I tried that, that was not my case either(the tank had properly isolated ground on one of the rca jacks).

In my case, the return of the reverb tank had too much gain and the drive was too low, so SNR was terrible and I had too much of the single coil buzz on the return.

Edit: my fix was to add 250uF caps to the drive cathodes, increase the capacitor into the drive 12AT7 a bit, use a 12AT7 instead of AU7 in the drive and reduced the gain on the return triode. At volume 10, full drive, the single coil buzz was still there, but it was satisfactory SNR.