I'll tell you a funny anecdote for your delection.

About 30+ years ago I had made an active loudspeaker system consisting of two satellites (mid-treble) and a subwoofer. This was made according to a Siegfried Linkwitz design.
I had bought 60W modules to power all 5 speakers, but at the time I was not very proficient. Some decades later I threw the electronics away and replaced them with DIY class-D modules (kits). That worked great.

Just I did not know what power they were outputting. In fact I was not interested in the power, but rather in the voltage headroom, in order to avoid them clipping.

So I devised a small µC operated analyzer that drove 10 LEDs, to show average and peak hold values, to give me a clue where I was. One for each amp, so 5 of those in total.

The unit was tested thoroughly on the bench. After installing, the LEDs did not register.
They did not show anything. Until I found out, that even after playing in the living room at party loudness levels (which you would not like to be subjected to for long), the power output was still below the threshold of the display: 1Watt. You would not believe how loud 1W is.

I then changed the code and installed a 10:1 "loupe" that automatically reverts to normal once the threshold has been triggered, before it falls back with a delay of a minute.

The measurement was by no means scientific, just a conversion using an 8 Ohm resistance, but it gave you a very good indicator.

The interesting thing was that the dance of the LEDs remained the same (the display being logarithmic), regardless of the power. It also showed that, beyond that 1W point, the wattage was climbing shockingly fast despite a perceived mediocre increase of loudness.

We all know that but it comes as a surprise when you encounter it.

Sometimes I tend to believe that they are doing things deliberately, but in case of the Marshall glue, I believe even the most benevolent glue manufacturer would have a hard time to foresee the effect of high voltage.

That said, the number of glues available is exploding. The market pressure is probably enormous and long time evaluation is self-excluding.

I'll order some SMP glue and report back in 10 years.

I use electronics-safe silicone, which you can get from places like digikey although it is fairly expensive compared to regular silicone. 
As you say, if you look around, you can find stuff that is neutral curing without the high price.

Some of the glues that have been used in the past have ended up breaking down over the years, and causing conductive paths that create various faults.  In many cases they are too difficult to remove and the unit becomes a write-off.
Some are not even that old, there are fairly new Marshall products now showing up that have glue which becomes conductive when in contact with high voltage (in tube amps).

UPDATE,
Printed off the diagram supplied by dmeek and went checking some voltages in the Psu area. Before I received the diagram, I had established that 330V dc was present at the main psu switching transistors. For some strange reason the unit came to life, the fan started running with both led's on the psu board illuminated. There was a hum from the speakers also. I straight away thought ''dry joints'' so I tapped all boards hoping to narrow down where the problem might be. With boards installed again and all screws tight (as one provides grounding on the psu board) the unit is now working. At this stage I have re-soldered all the psu board as transformer legs are the first port of call when checking for intermittency.
I welcome any comments.

### Returned to it this evening and tapping the rear input board caused drop in audio level with hum. This turned out to be the contour switch at the rear. I will soak test over the next few days.

Quote from: Jazz P Bass on April 18, 2026, 07:10:53 AMHave you tried contacting Peavey by E Mail>

Thanks for your reply.
That was going to be my plan B but thanks to dmeek I am now sorted.

Thanks dmeek for the schematic and greetings from Ireland.
Just saw your reply now.
Now the fun begins.

This might be it

You cannot view this attachment.

Issue has been resolved. Here's the deal with these and the 320t mace amps. From the inputs there is a dual conductor shielded cable carrying the guitar signal to the normal channel. This is the red wire coming from the shielded cable terminating in the circuit board. There is also a black wire in the same shielded cable which carries the output of the normal channel back to the input jacks where it is fed into the effects channel when plugged into the series input, thus creating the two channels in series scenario. The input wire and the output wire for the normal channel are running parallel and literally touching each other inside the shielded cable run for about 10 inches, this is a major no no in guitar amps. It doesn't matter that they're in a shielded cable because they're not shielded from each other, them being in a shielded cable together probably makes the feedback loop worse. I removed this dual conductor shielded cable and installed separate shielded cables for the input and output of the normal channel and every bit of the squeal is gone. The high end fidelity of the amp is also greatly improved. I would recommend this mod to any and all deuce and mace amps that run the input and output together in a single shielded cable.

Have you tried contacting Peavey by E Mail>

Hi All,
I am helping a friend out with his totally dead PVXp12 power speaker.
After initial inspection I discovered that it runs a switch mode psu so I now require a schematic .
Maybe someone could post one here or PM me. I have tried all the usual sources but no luck.
Thanks in advance.