Help Help! (Strange issue Barley any volume on all channels)

So weird, Mark V worked fine last night into my Diesel 4x12 and now it is doing something weird.\


I get almost no volume on all three channels. I raise and raise the master and some sound comes out but very thin and not very audible.

However.......When I flick the on/off switch to off.................... the tone comes back for a second and dies off as the amp powers down. Did this a few times.

Any ideas what this might be?

I checked my cables, guitars etc. Plugged stragiht into it with nothing in front and the same problem. (I have a JC-120 right next to it and I plug in the same guitar and cable and have no issues.)

Thanks in advance.

Check v7 preamp tube.

If V7 does not resolve the problem....

Try the other 8 ohm output or one of the 4 ohm outputs (that would be safe if you cab is 8 ohms or less).

Is the effects loop active? If so, place it into hard bypass. If that corrects the problem replace V6 (Circuit B is used for effect return). Had a simiar issue but it only happed once in a while while using the effects loop in order to use the master volume control. Also, verify the solo control knob is not pulled out (mute). You can also try disconnecting the footswitch and use the channel select knob in the rear to see if any of the channels work without the remote footswitch control. I have had issues with the footswitch cable (poor connections) that caused some intermmitent issues.

If that does nothing, turn off the reverb. It may be loose connections or V4 (A circuit reverb send) V5 (b circuit for reverb return).

Did you resolve your problem?

Make sure the tune/mute switch is off. (solo knob on the amp is a pull switch pot) I took my footswitch to work to check the solder joints on the 8 pin din connector. Who ever built the footswitch or decided to use a screw to make contact from the PCB to the base was an idiot. The screw that is used as a ground pint for the switch plate forms a cheap connection to the base by compression. That causes severe flex on the circuit board. Bending the PCB will damage copper traces, crack solder joints (they use lead free solder so it is more brittle than lead based solders). I removed the scew and replaced it with a short one, added a wire with two ring connectors and mounted one end to the base to complete the ground circuit. No more flex, have not had the footswitch toggle between settings if you move the cable. I had resoldered the 8 pin connector too. After repair, plugged it in and no sound. Nothing. Then realized the mute switch was on.