Musicians Roadhouse

I have a 50 watt VM that looses signal at C13's output. Goes from a nice good looking waveform to zip.. All the valves test just fine on my Orange VT1000 valve tester.
Any clue why this has gone awry?
Cheers

If c13 was open you should still get a partial signal through the bottom of the stack. Is the signal passing the other points in the stack?

There's signal all the way thru, it has the bottom clipped off and looks ugly. It starts at the Treble cap. I can plug right into the Effects Return and signal looks good there through the output. But the culprit is before starting with C13...

C13 could be bad. I have seen silver micas literally crack open before and cause irregularities in the signal. Same for resistors. Now when you say plug into the loop you mean you are injecting a signal at that point?

What are the dc voltages either side of C13?

On the 33k side there's 175v. On the other side there's no voltage( the side that goes to the pot).

I swapped out the 500pf cause it was easy and That seems to be where it starts.. No difference. If I turn the Treble pot off/down the signal goes up, but still the bottom 1/2 is semi-lopped off. The OP tranny has a physical hum/vibration to it so wondering if there's an issue with it. When the amp is on Standby it's not there. Only there when it switched to "On" and the B+ voltage is present.
Thanks!

Can you post a pic of the waveform?

Those dc voltages are ok

Does it make any difference to the waveform when you enable/disable the FX loop?

How about if you unplug CON2 altogether thereby totally isolating all following stages?

Top shot is with the "Dynamic Range" button pushed in.t Loop is engaged

SteveD wrote:Those dc voltages are ok

Does it make any difference to the waveform when you enable/disable the FX loop?

How about if you unplug CON2 altogether thereby totally isolating all following stages?

O.k... I feel pretty stupid here as with the loop off the amp looks just fine. When the loop is engaged is when the signal gets ugly.
I'm going to try a patch cable between the In & Out and see what happens when I activate the loop..
With a cable inserted and the loop activated it's the same(didn't think it would be any different.. ).

With Con 2 disconnected there's barely any signal passing at all..
The owner of the amp uses the loop for his "Helix".. I would imagine that the Helix is what screwed the loop..