Recently had great success getting a fix with a TH500 Amp repair where both the amp stage and the PSU had faults although no circuit info was available it was possible to get a repair.
These popular amps consist of an ICEPower combined class-D amp and power supply module. The power supply powers the Aguilar pre amp PCB attached to the front panel. It is a simple design and should be reliable as long as ventiallated properly.
The modules are replaceable in the worst cases but are fairly expensive at around £250-300. However I have successfully repaired a few of these now so for some faults it is definitely possible.
The pre amp is a fairly simple circuit and should not give much trouble apart from damaged front panel items like pots jack sockets.
So if you are having trouble with a TH350 or TH500 or any of the aguilar amps for that matter don’t give up hope. You can arrange a repair either face to face or remotely as these are relatively cheap shipping.