Get ahold of Fender for the schematics, it may even be on their web site.  Certainly way too large a file for me to post.

Without looking it up, solid state power amp needs positive and negative voltage supplies of some 40v or thereabouts.  I don;t care if it is 40, 45, 50, 35.  I just don;t want it to be absent.  And the op amps and low voltage stuff will be using +/-15VDC supplies.  Digital circuits will be using +5VDC.  I don't know offhand if there are relay supplies or if the couple tubes have heater supplies.  SO that looks like at least 5 supplies to check.

And alternatively, while most solid state amps pop at turnoff, if you have for example an op amp in those preamp channels that has gone to DC on an output pin, that could be the cause of a lot of hum and would make turn off pop much louder than otherwise.

Then start at the start, are all power supplies present, up to voltage, and clean?

Get the schematic set from Fender.

Hi, your terminology is confusing me.  If I get you, there is no output from the speakers, right?

"The output MOSFETs are heating..."   Um, this amp has no MOSFETs, do you mean output transistors?  And by heating do you mean overheating?

If the amp likes to be quiet, check the headphones jack.  There is a contact in that jack that mutes the amp.  if it gets dirty, it can mute when you don;t want it to.   Also, try plugginf into the two FX returns with a guitar.  Does that come out strong?

I don't get what you are saying about R34.  R34 is the ground return for the speaker.  The headphones jack completes teh speaker circuit to R34.  When plugged into the phones jack, the circuit to the speaker is broken, but R34 remains as the path to ground for the load.

R31, R34 are where they are regardless of which load is selected: either the speaker or the phones with 680 ohm resistor.

I have no idea what it means the 2050 is poor quality and can't handle the input.  Is the MP3 player TONS louder than a guitar when plugged into the CD jacks?  The chip just amplifies music, it has no idea where the music came from.  Your guitar, or a recorded guitar are all the same to the 2050.

If the amp worked when you got it, then it worked.  How would someone know when the IC was about to die?  I have made a living fixing this stuff for decades, and I have to say I sure cannot tell you that an IC will die in a week.

Is your expensive silver compound electrically conductive?  That would be a problem, since the whole point of the insulating mica is to isolate the chip electrically from the heat sink.  And no matter how good such stuff might be, it doesn;t prevent parts from ove3rheating.  WHat it does do is keep normally operating pqarts from overheating due to lack of dissipation.  But if the part is being overdrivien, or faces excess voltage, or faces a shorted load, or any one of a bunch of things, it will get hot.

That explains the heating resistors, but he is still sorting out the damage the overvoltage did in the poper amp.

He's on other boards with this.  His PT wires were mixed putting 70vAC across one side of the bridge instead of 35v.  SO instead of 50VDC he had 90VDC dropping through the resistors to the zeners.

Not only is it assumed that everything is on the internet, the corrollary is that if a company doesn;t show some item on their web page, they must not have the item.

This should be the power amp drawing.

NTE is a brand of general replacement semiconductors.  They have a big book that you look up your transistor type in and it shows their "crossreference" type.

I for one have never seen an MPSA06/56 that was not EBC across the front.

I don't know what I am supposed to see here.  If the amp tech is competent, he doesn't need pointers.   I see those two main filter caps sticking up, they often need to be resoldered.  On ANY amp with intermittent problems, check the solder on anything with mass or that sticks up from the board... like those caps.   Any of those rectangular cement power resistors can shake loose.   Jacks and controls along the panel deserve a solder look.

I rarely think of age.  Guys all the time ask when an amp was made.  I think, how should I know?  I don't care.   I leave that to the fans.   I don't mean it unkindly, but I call the folks who can tell you every model and year amp fans.  The guys who can quote chapter and verse, "Oh the master volume didn't come out until 1974, and then the pull switch was added in 1977, and..." or whatever.  I call them fans, like the guys who like to rattle off baseball stats.  More power to them and bless their hearts.

Jukebox people are the same way.  They want to tell me what year it was made, but I want to know what model it is.

But to me, I think in terms of how things are made.   Old Fender is galvanized heavy steel chassis, Modern Fender is formed sheet steel like these wedgies.  Old Fender is eyelet boards and caps up under a cover.  Modern Fender is large pc board.  I don;t care how old it is within those categories.

If the fist method seems too hardcore, go to the tool store and get a rubber mallet.   I have several of those too, but geez, sometimes they are ALLLLL the way across the shop, and I don;t want to walk that far.

I call those Fenders "wedge chassis" amps.  The chassis is narrow at front, just the control strip, but in the rear the panel is like 6-8 inches tall, so the bottom of the chassis slopes.  So from the side it would be wedge shaped.  Well, to me anyway.

For some reason, any time I see one of their SS amps built on that style, I expect to find loose filter caps.

In my experience, your problem is that the two main filter caps have broken their solder - well one of them has anyway.  FLip over the board and resolder the four filter cap pins.  Don;t decide some "look OK" just rsolder them all.

There are a number of Fender solid state models constructed similar to yours, and this is by far the most common failure.

Here is a test:  with the amp running, turn the controls all to zero.  Now ball up your fist and whack the top of the amp hard.  Does that make the amp either start humming or stop humming?  If the amp does anything in response to that blow, then there is a loose connection inside.   You might suggest to your tech person that the amp sounds like a loose filter cap or something that sounds like one.

Wait, WHICH transistors went in backwards?  How did the pinout become different?

Please tell me you are not using NTE parts.  Real parts should all fit the same way.