Fender Hot Rod Deville - Drive channel no sound - weird voltages

[spunko]

Hello friends. The clean channel sounds good, but drive channel no sound at all.

I took some readings on the low volatge supply and they are good when the amp is ON standby OFF, but if I swicth it to operational (standby ON) those voltages go crazy (picture - red text).
I managed to take out one lead of each zener diode (CR13, CR14) just to do a quick diode test with my multimeter and they seem to be good. R78 and R79 read 330ohm on spec.

What could cause those voltages to change so bad when the amp is operational?
Thank you very much.

[AlNewman]

Do you have a LBL?

What are the voltages at the power tube grids with S/B on/off?

[spunko]

Do you have a LBL?

What are the voltages at the power tube grids with S/B on/off?

I'll post those readings when I get home, went to get some pizza with my daugther  . I forgot to mention that the readings on the picture were taken without power tubes, just pre amp tubes.

[WimWalther]

Just a suggestion, be careful about using terms like "Standby on" and "Standby off", they can be very confusing.

[Latole]

Just a suggestion, be careful about using terms like "Standby on" and "Standby off", they can be very confusing.

You are right; confusing. electrical speaking, in "standby on" amp can't play. Ap is on "standby"

About amp standby, I always use ; amp in "play mode" or amp in "standby mode"

[AlNewman]

It may be useful to post your voltages on the schematic vs the layout, it's difficult and confusing to cross reference parts from a layout diagram.

I would think most everything in the low voltage power supply could be suspect, but the only things (that I can see) that would have an effect on voltages when amp is in "play" mode would be the power tubes or perhaps a leaky coupling cap?  Otherwise it could be a bad diode, shorted cap, bad solder joint, etc. in the power supply....  That's just, like my opinion, though man, I'm sure others could have more useable input.

I do happen to have a Deville here, and all your switching and LEDs should still work in "Standby" mode, or switch "open". 

[spunko]

Thank you for all your replies. I try to translate as we speak here. For us "prende y apaga" is "ON / OFF" if we reffer to the stanby switch we tend to say "Standby ON / Standby OFF", some sort of bad translation that turned out into idoms  I thought it will be confusing, that is why I mentioned "operational". I will say play mode or standby mode from now on 

I couldn't work on the amp this weekend. Family activities, and a JCM900 that needed to be on the stage soon and was smoking with a loud hum I'm going to post what I've found on that one.

Well, today I took a look on the fender and noticed a broken ribbon cable (P3A - P3B). As soon as I touched it, the amp went back to the spec voltages in play mode, touched the cable again and the voltages went nuts. I'm going to replace it tomorrow.