Marshall JCM 2000 reverb query

[Eagle77e]

I`ve got a JCM 2000 TSL 60 Marshall head. The reverb no longer works. The Reverb Led on the footswitch lights up, all reverb knobs on amp are full, I`ve tried another reverb unit (which I know works) on it but still no luck. Are there any other simple things I can explore ?

[drewl]

pull the rca jacks off the tank, the reverb return one will "buzz" or hum when you touch it with the reverb level up, if so the return circuit is amplifying the reverb signal.
The other rca jack will be the reverb send signal to the tank.
the guitar signal should be present here and can be monitored with an oscilloscope or you can check for a varying ac voltage with a voltmeter as you play the guitar.

[Enzo]

And please check the cables themselves. Sub in a set of cables from your home stereo if you like.