Since the top usually hosts a majority of the components we might be interested in, let's start there. Given how the two heat sinks cover nearly everything of interest, I decided to go with an angled shot. Most of the 5VSB and auxiliary components, the main points of interest, are along the board's front edge anyway.
Hidden under the primary side heat sink on the right, there is a substantial pileup of EMI filtering components, one input filter inductor, a chunky toroidal inductor for active power factor correction, the APFC and main converter MOSFETs in TO-247 packages, the APFC diode in TO-220 packaging and the 400V 220µF Fuhjyyu main input cap poking out in the top-right corner.
On the primary side of the 5VSB/auxiliary transformer, we find a 50V 100µF capacitor that appears to be the main auxiliary output filter cap, a 50V 22µF cap next to it that's presumably part of the primary side's feedback loop based on its proximity to the photocoupler, along with a handful of diodes and resistors.
The secondary side offers little worth noting. Aside from the usual crop of output filter inductors and rectifiers, we do have the following list of visibly strained capacitors:
- a weepy 10V 4700µF Fuhjyyu TMR on the 3.3V rail – the tall blue one on the left
- a pair of slightly bulged 10V 2200µF Teapo SEK for the main 5V output hidden under the heat sink, one of them partially visible just above the TMR capacitor with a blob of brown-orange adhesive on top of it
- a pair of 10V 1000µF Teapo SEK for the 5VSB output near the bottom edge
Does anything else stand out on the top side? Yes, there is one fairly clear sign of something gone wrong if you look closely enough.
While looking around for capacitors that show an obvious need for replacement or other obvious issues, I noticed a discolored area around the diode next to the 5VSB transformer labeled ZD4. The device in question is a 1N4746, a 18V 1W zener diode. Does it get that hot by design? Did it get that hot due to a failure elsewhere? Did it fail? I powered up the unit for a few minutes, turned it off and felt around but could not find anything that appeared to warm up significantly apart from the 5VSB dummy-load resistor, which was getting scalding hot from having four times the power it is supposed to draw going through it due to the 5VSB rail rising to twice what it should be. This is one of those situations where a thermal imaging camera would come in really handy: watching the whole board warm up in real time makes finding unexpected hot spots orders of magnitude faster, safer and easier.
Considering how hot a printed circuit board must get before it starts darkening like this, everything in the vicinity becomes a likely suspect. Even the printed circuit board itself might be in question if the charring got bad enough to start conducting enough to interfere with normal circuit operation.