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Re: Crate 100 head. Reverb doesn't work.
Check the input RCA plug going into the reverb tank (silver box with two wires connected to it). Make sure the amp is off when you do this. Sounds like the output is working fine if hitting the amp does it.
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If it has a effects loop output and input on the p.a. head and a in and out on the reverb effects processor, then yes you can, just run the effects loop output signal into the input on your reverb processor, out of the output back into the input effects loop on the p.a. head, kinda like you would a effects pedal thru the effects loop of a guitar amplifier. hope this helps!
items to check are
1-the footswitch and plug
2-the reverb unit ,usually found at the bottom of the box
3-the reverb unit is plugged in to the amp
4-V6 a 7025 valve
5- the reverb switch is in the on position
Notice that the reverb is set by DC voltages from teh setting pots that go to the DSP chip. These setting pots receive voltage from a 16 volt ZENER regulated source. First thing is to CHECK that voltage. If the Zener has opened and you find much over that 16 volts, that is your cause of the problem.
The circuitry is on page 1 in the 3B to 3D lower left of the page.
There are two coils in the reverb unit which use delicate wires which can break off - these can easily be checked, as follows:-
i) Remove one cable plug from the reverb unit & substitute an uncapped phono plug to the socket.Then check that there is electrical resistance across the plug terminals.
ii) Reconnect original phono plug & do same test as i) to the other socket.
iii) If either is open-circuited, then look for a break in the lead-out wires from the corresponding coil inside the reverb unit. This break may be repaired (contact me for details) or buy a new reverb unit!
iv) If there is electrical resistance at both sockets of reverb unit, then clean both original phono plugs & try the system again.
Looking over the schematic I see all sorts of poor design. The reverb is driven by IC TL072 chip and the output is received by the same.
This chip is supplied with +/- 15.5 volts UNREGULATED which is stupid! If you get a power surge, the IC will be destroyed. Myself I would put at least a shunt Zener regulator on these voltages. Use a 100 ohm resistor in series and Zeners to ground for both the plus an minus 15.5 lines.
First thing check those 15.5 volt... the plus is on C23 pos term and the neg is on C24 neg term.
They have a 1 meg resistor to ground from pin 3 of the chip to bias the + input of the chip. This is TOO big as the input leakage current can be too much. I would reduce this resistor to 220K and increase C22 to 0.0047 mfd.
Check the DC voltage at pin 1 of the chip (IC1). It should be VERY near zero.
The output buffer for the reverb has better design. Check for zero volts or very near it on pin 7 of the chip. Be careful not to short to pin 7 which is pos 15.5.
If either of the above tests show a voltage over 0.5 volts from ground, replace the TL072 chip as it is likely fried by power surge..
Since there is high voltage (320 volts) use great caution when working on this amp.