I have one for a TU100A, which is similar except for the Aphex exciter circuitry. However that piece and the ALC is shown in Bogen's TPU-15A public manual.

But before you take anything apart, take some simple steps like turning off the Aphex and potting the Music Mute fully clockwise. Make sure your inputs aren't cranked all the way up and set the ALC about halfway for starters. There is a little art to tuning power amplifiers and I find most don't know how to do it. I believe the basic steps are either covered in their TPU100 and TPU250 manuals, but if not I'm sure you can find them on Bogen's website.

Now if you would rather attempt repair yourself (instead of Bogen, which I recommend) you might look at one of the six power transistors along the black heat sink that divides the circuit board. But check the action of the fan and thermostat first; I'll bet you had a failure there first.

"Press play and record at the same time" -- Tim Alberstein