I have a Peavey XXL (solid state) amp on the bench. Sounds great until you flip it to the Ultra channel then its squeal mania. It happens across all volume, gain, and eq levels and with different guitars, cables , etc. The issue is in the amp, in the Ultra channel only. The squeal goes away when your actually playing but as soon as you stop its there piercing your ears. Where should I start? I plan on getting it hooked up to my oscope today to see if I can see it.

That sounds feasible to me. It does have a 24v fan in it, so a simple circuit may be the right answer. I will call Fender today and see if thet tranny is still available (I figured it was an outdated part). I do like the idea of planting a smaller second transformer inside as there is plenty of room.

Transformer nonrepairable. I didn't have any luck yet finding a replacement either with those specs.

So the brown wire should be at 22 volts correct? If so I'll get a look at the transformer connections inside to see if anything came disconnected. Should I still disable the fan circuit for further testing or are we at a standstill until I fix/get a transformer?

Yes, wiring hanging in the air. P#'s only added for reference. Thanks for the help so far, always a pleasure here!

I have a Sunn Stage Lead, best sounding SS amp I have!

Ok, relative to the red/yellow wire (P6)
red (P5) - 53.6VAC
red/wh (P7) - 53.5 VAC
brn (P8) - 0 VAC
brn/wh (P9) - 22.4 VAC

Well whatever shorted did cause quite a show, I am not surprised. I'll take a look at that tranny. The overvoltages with an open winding doesn't make much sense to me either.

Voltages between P8 (brn) and P9 (brn/wh) is 0VAC.  P8 to ground is 0VAC.
P9 to ground is 22.4VAC.
A = red wire
B = red/yellow
C = red/white
D = brown
E = brown/white

A has continuity with all but D
B has continuity with all but D
C has continuity with all but D
D has no continuity with all
E has continuity with all but D

Transformer wires are correct. No voltage on P8 or P9 to ground unplugged.
No doubled wires on posts.
Only 5 secondary wires.
I have to take board back out to disable fan rectifier, will try to get to later tonight. Fan does come on as soon as amp is turned on.
The floating piece of metal was found on D112 of the fan circuit just a FYI.

P5 (TP1) - 54VAC    52.9VAC
P6 - 0V                    0VAC
P7 (TP2) - 54VAC     51.9VAC

TP3 - +72VDC         +70VDC
TP4 - -72VDC           -70VDC

P8 (TP5) - 23VAC       43.2VAC measured this 3 times
P9 (TP6) - 23VAC        22.4VAC

TP7 - +30VDC            +56.2VDC
TP8 - -30VDC              -55.9VDC  measured also 3 times

0VDC between P8 and P9 unplugged.

R161 is 11.2 ohms

QuoteDoes this mean +70V at TP4 and -70V at TP5?
How can you have +70V at TP4 which is a negative point?
Please confirm.

Sorry I mixed those up...-70 at TP4 and +70 at TP5 like it should be. I'll recheck what you have requested.

Quotewhat is the mains voltage where you are?

110 volts USA

QuoteWhere are you placing the negative/blackmultimeter probe?

To ground at the chassis AC ground

Bad transformer?

I didn't remove any of the board wires, but doublechecked anyway, all wiring is correct per schematic and board labeling. I measure +70/-70 at TP4 and 5. Resistance check from TP5 to ground is continuity.

Voltage regs:
U101
Pin 1 - +55.9V
Pin 2 - 0
Pin 3 - 0

U102
Pin 1 - 0
Pin 2 - -56V
Pin 3 - 0

Power to voltage regs but nothing on the output side.
I will check the other test points per Mr. Fahey