Fender '65 Twin Reverb Repair

[samuel.brunner]

Hi everyone

I bought a second hand Fender '65 Twin Reverb reissue with the reverb not working (which was clearly communicated and which resulted in a lower price). If possible, I would love to repair the reverb and while my search on forums, YouTube, etc. yielded many results, none resolved the issue with my unit so far.
As far as I understand it, there are a couple of possible parts which could be the issue:
1. Footswitch
2. RCA Cables
3. Reverb Tank
4. Something on the circuit board

for 1. the footswitch, I have not been able to try it with a different footswitch unit. However, I read that if no footswitch is plugged in, the reverb should be engaged, but if I disconnect the footswitch, there is still no reverb coming from the amp. But in a YouTube video, someone demonstrated that with a working footswitch, when pressing the reverb button and having the reverb turned up on the amp, you can clearly hear an increase in noise from the amp, even without the reverb working. This is not the case with my unit, when I press the reverb button, there is no sound difference audible.

2. Although the cables look good, I tried to connect the tank to the amp with some RCA cables I had lying around from my record player, which did not resolve the issue.

This leaves me to believe that either 3. the reverb tank is the problem or 4. something on the board, which I would probably not be able to fix. Do you have an idea how I could test, whether it is the reverb tank? I do not have a spare one to try out. Or do you have any other ideas, how I could isolate the issue and go about fixing it?

Thanks a lot, cheers,
Sam

[LOUDthud]

Measure the resistance across each jack of the reverb tank. What did you get ?

[Stevem]

You only need a foot switch plugged in to turn the reverb off on the fly.

If you have a rca cable then unplug the reverb pan and jump the jacks with the cable .

If turning up the reverb then acts like a volume boost then all within the amp is at least good.

[FUCHSAUDIO]

Here's my free "super five minute reverb diagnosis":

Plug RCA cable into return jack, turn up volume, touch tip. Do you have buzz ? If the return works, plug in the output of the pan. Shake pan. If you get clank, output of pan is good. Switch pan wires, shake pan. If you get clank (reduced volume), then input of pan works. (you are listening to the input end of the pan) Plug test speaker into reverb output (pan input connection), put signal into amp and see if reverb output has a signal. If it does, run a jumper from send to return. If raising reverb volume increases amp level a lot, then reverb circuits work properly. Likely bad pan. If you have no send signal, it could be a bad driver tube (12AT7) or cable or reverb transformer. If you have no return signal, could be bad tube, cable or something on board. Not much else to check beyond that...

[Stevem]

Many times the failure point in a pan is one of these small wires from the transducer braking off at the rca jack.

These can just be soldered back on, but some times the transducer itself goes open.
You can test this with a ohm meter at each rca jack with the reverb cables unplugged from the pan.

The input side will test out at less then 1 ohm, the output side of the pan will test at over 1700 ohm.

If you find that one of these two reads open then it’s time for a new pan.