What is wrong with my reverb?

hi. the reverb on my 112 RD-100 sounds really bad. it sounds faint and not very ballsy. even turned up to 10 it is wimpy and has little decay or depth. do i need to replace the tank or is there something up with the cicuitry of the amp itself? the reverb is supposed to sound good i take it. are there any diagnostic things i can do myself? repair guys around here won't touch anything for under 150 bucks.
when i use the insert jacks and an external reverb all is well...but i'm sure the insert jacks don't share the same part of the circuit as the send/return to the reverb...
any ideas would be great.
thanks,
LL

Some simple tests to help you diagnose...
Does symptom occur with/without the footswitch
plugggd in?
Do you get any 'snap crackle pop' if you
move the reverb send/receive wires around?
If you 'hit' the reverb unit when it's on
do you get the characteristic 'Boing' of the springs?
Are all the reverb's/chassis RCA jacks CLEAN and fit TIGHT? connected correctly? (see schematic if needed)