No power, fuse blown, found mosfet switching transistor shorted in PSU section, perhaps due to a power spike, and usually other stuff blows, but could be lucky and only be that…
Mosfet (STB36NM60ND) was a pig to get out as not much space and the heatsink soldered to the board, but a combination of hot air, chipquik and flux managed to do it. The mosfet (same N-channel) on the back of the board also shorted and much easier to remove.
STB36NM60ND were unavailable for months (chip shortages) so ordered NTB110N65S3HF replacements (as not got any suitably high rated D2PAKs in stock).
Replaced the L6599AD Resonant half bridge controller too as had suffered damage, reinstalled but still wasn’t right, mosfets overheating within seconds.
Turned out the cause was something very strange…
Big inductor with a severed pin… Never seen that before, the pin got sucked right up the desoldering iron!
Rear of board with new Q5 mosfet and holes seen where inductor goes:
Top side also, before cleanup
Securely attached a new bit of copper wire leg and back in:
Gave the fan a clean whilst in there
Soak tested on 1000W dummy load and all good. Nice little efficient and powerful amp!
Screws hidden under the carefully peeled back label the customer had left on:
All good and customer happy!