Seems to be a thing with these chargers. This is what I have failed on this one:
R2 (470 ohm), R3 (220 ohm), R4 (150 ohm), RS1 (0.43 ohm) - all open circuit
Q1 (NDF04N60ZG) - shorted
IC3 (SG6848) - probably blown
The above components are PWM control and the main chopper transistor on the primary side. Normally a blown chopper will take out the main fuse, but there isn’t even one in this design. Instead they rely on RS1 (fusible resistor I’m assuming) to go open when the chopper shorts. This is a really crappy design, since the main filter caps would be a at 400V DC in the fault condition. There’s no bleeder resistor incorporated either, so if you go working on this, make sure you discharge the cap.
D3/D9 (SB5200) - one shorted, other ok. These are the main rectifiers on the secondary side. I’ve seen this go short in other supplies, but good designed ones will shut down the PWM to prevent damage. Not this one it seems.
Q2 (9565BGH) - Shorted (in fact had a hole in it).
Q4 only reads 0.6V on two pins, but I suspect this is actually a zener diode in a SOT346 package. Only see 202 or 702 on the package. Be nice if I had a schematic.
Just an awful design as far as switch modes go. Haven’t seen this much destruction since the old days of self oscillating supplies. Anything with a PWM IC usually has over current/voltage protection to shut everything down. Just a poorly designed and CHEAP supply. I was half through repairing it and I’ve now decided to bin it. It’ll only blow up again.