No output from 5150II

[frozen]

Having an issue with my 5150II head. I lent it to a friend for a few weeks. It died the day before he gave it back to me, he says it worked fine one day, and the next, nothing.

The power and standby lights come on. Switching the standy light to "On", the light goes green (as it should), but there is no output from the cab. The Preamp tubes warm up, but the power tubes do NOT. No glow, no warmth. I plugged a set of headphones into the preamp out and there was nothing.

Things I've checked so far:

-All fuses are fine
-Output transformer primary reads 30+Ohms between each leg, secondary reads 0 Ohms between the legs? I emailed Peavey and they said this is correct for this tx.
-I have ~500V at the screen & plate.
-I've checked the big 5W and 10W resistors, they are fine.

I'm an Electrical Technologist but don't have a lot of experience with amps, can anyone offer some guidance? The tubes were replaced with JJ 6L6's about a year ago, and I doubt 4 tubes would all go at once?

Any help would be appreciated.

Mat

[Amp Kat]

Try to patch a cord from the send to return jacks. Also try using the preamp out or send to another amps return jack then use another amps preamp out or any signal to the power amp return of the 5150 II and see if it works.

[Enzo]

The clue is the power tube heaters are not coming on. No heater, no tube function.

The 6VAC from the power transformer is not getting there. There are some gray ribbon cables that carry the 6v current. I bet one of the pins is burnt or the solder to the pin headers is cracked.

[frozen]

Thank you Enzo! I think I've located the problem, definitely in that circuit! Thanks alot!