Dual rectifier FX problem with SOLO and OUTPUT

Hi my friends! My dual has a problem with fx loop. When fx loop is active SOLO and OUTPUT doesn't work properly, sounds very low. in bypass all channel master works and the volume is perfect. I thought was V4 but isn't.

Still with the problem

What happens when you jump the loop with a cable?

VisaL said:

What happens when you jump the loop with a cable?

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I did It but didn't work.

What is the SEND level at in the rear? That is always in the circuit, so if you have the send set really low, you'll have very low output. I usually keep it right in the middle.

Both in the middle.

V4 is the obvious as it’s for both the send and the return. Intermittent loop jack is another, but since you’ve ruled out those, I think there’s not much else you can do without getting the chassis out and start poking around. You could further narrow it down running the signal from send to another amps return to see does the send provide decent signal. If it does, then problem is between return and V5. Could be wire from pcb to volume coming loose, faulty pot or one of the mute circuit fets.

I'll test the signal out another amplifier. Thank you, I will continue with this issue since I have not found an answer anywhere and I have read the problem of others, but no one has the answer to the problem.