Fender amp reverb's driving me nuts!

[Analog Assassin]

Okay, this should be an easy fix, but it's eluding me. The reverb on my super reverb just doesn't work. If I take the reverb tank out and shake it, I can hear some faint reverb, but not the loud 'crash' I should.
Here's what I've tried so far:
Tested the reverb cables. Test good with a continuity meter, no shorts.
Swapped out tubes no. 3 and 4. No change.
Plugged in the reverb tank on my super champ. No change.
Tested the continuity of the wires to the reverb pot. Pot seems to be functioning fine, but I don't get any change in the reverb level, albeit small. It doesn't get louder or quieter, it stays the same.
Going by the amp's layout schem, the voltages I'm reading are close enough (within the 20 percent tolerances) of the voltages I should be, according to the schem.
I unplugged the cable from the reverb tank that goes to the reverb return circuitry. Touching the tip gives some hum.
I don't know what else to try, and it's driving me nuts. It's a simple circuit, why's it eluding me?
Thanks.

[Tom Phillips]

Did it ever work since you had the amp? If not, the tank could be the wrong type.
Any chance that the reverb tank leads have gotten reversed?
Try swapping them at the chassis jacks to find out if the reverb starts working.
Tom

[Analog Assassin]

Yeah, it used to work. Since I posted, I found some other RCA cables and tried them out, also no go.
I tried swapping the cables around to see if I mistakenly put them in wrong, but that didn't work, it wouldn't give me any sound then.
I've been studying the schematic and layout to try to see what it can be, but no good so far.

[wizard333]

Did you try putting a different pan in there? The wiring in those pans can go bad, the springs can even break. Take it out of the bag and look at the wiring... any obvious loose wires? If its not something you can easily see, they are a pain to repair and at $25 for a good new one, its worth the save in headache just to replace it.

[Enzo]

OK first isolate the problem. The drive end and the return end are separate circuits. Take the pan out and disconnect it. Heasure the resistance of the transducer at each end. Do this at the jacks on the side. The OUTPUT end should measure something like 100-200 ohms. The actual resistance doesn't much matter, it is open or it is OK. Open means the pan is bad. Same at the INPUT end, though the resistance there will be MUCH lower. Again, all we care about is whether it is open or not. Open is bad, continuity is good.

Once we know the pan is good, we check the amp. DO not assume you have only one problem. You could have a bad pan AND an amp problem.

Before installing the pan, turn the amp on and the reverb up half way. Without touching the shielded part, touch the tip of the return cable. Hum results. You mentioned you got hum, but was it LOUD hum? Touch the return cable tip on some working anp for reference. If the hum stays diminished, then the return circuit needs help. If the hum is fairly loud, then the return is working.

By the way, in case there is confusion, that is how to determine which cable is which. The one that hums when yuo touch the tip of it is the one that goes in the OUTPUT jackon the pan.

The drive end can be checked too. You can pull the RCA out of the reverb pan INPUT jack and with an adaptor plug it into the input of another amp. Got a reasonable signal? This is the same idea as when we plug the output into the normal channel of an old Fender to make a spiffy reverb control out of the channel. In fact, the drive circuit is really just a tiny power amp. Little singler ended mini-champ sorta. COnnect the output cable to a little speaker. Hear anything?

Once you know WHERE the problem is, you are much better equipped to figure out WHY it is.

[Amp Kat]

There are also some reverbs in reissues that have the switch in the back for dfifferent channels. Make sure it's in the right [position. You can also scope it if you have access to a scope before the reverb tranny and after and going to the pot wiper. It will get slammed pretty hard by the tranny and driven back up by the reverb recovery stage. Most of the reverb problems I've found unless the pan is bad are connection problems where the cable looks like it's making contact and isn't. The footswitch jack can cause it to on certain models. The scgematics have have pretty usefull test points so may check that out.

[Analog Assassin]

Enzo, AmpKat,
Thanks for your replies. I'm going to go through the checks you mentioned, but so far, I think it's in the return section, and even further, I think it's around the reverb pot. It gives hum when I pull the return jack out slightly, but the volume doesn't increase or decrease when I rotate the reverb knob. It should, because it sure does on my super champ. I put my meter set to resistance on the .003 cap and the 470k resistor and turned the knob, the resistance varies along the 100k route, so I would think the pot is good and so are the wires there. I'm going to do some more testing, but thanks for your help so far.

[Analog Assassin]

I got it figured out. I replaced the .003 cap, and soldered one end to the wrong connection. Thanks for all your help.