Marshall Mosfet 100 (5213) Reverb Not Working, Also not the tank

[lespaul924]

Hello, I have a marshall mosfet 100 combo with dead reverb. I can hear the tank (accutronics 4DB2C1D) splash when moving it, but no effect while playing. On the Oscope there is signal going to the pan input jack, but no signal on the output jack back to the amp. Tried a new pan and same thing. also replaced IC4 drive/recovery 4558 opamp. Voltage rails are good+-15. the footswitch transistor TR7 base has .7v to 0v when on or off. The signal at the drive section and pan input jack doesn't make it through either reverb tank to the recovery section, yet I can hear the springs splash. Any ideas? Thanks

[Enzo]

You have signal on the hot lead of the reverb IN. But is the circuit complete? What if the ground return from the pan is open? Look at IC4a pin 1. Power off. Measure resistance from that pin to ground on the circuit board. Not just chassis ground. Do you get the 100 ohms of R42 plpus whatever the reverb pan input coil resistance might be, I am guessing a total of maybe 200 ohms or so?

And how large is the signal you see at the reverb pan input?

[lespaul924]

thanks enzo,ic4 pin 1 and ground is 320ohms. the signal is strong on the input, springs show a little something on them, nothing on the output. Thanks again for the response

[lespaul924]

bump