I am working on 12V 30A smps that has only 1V output. I haven't got board's schematic but I found one same like mine (Schematic Link).
- I measured high voltage capacitors (C2 and C3 on the schematic.) and bridge rectifier. They are working.
- Also checked power switching transistor on board they seem fine. (Q1 and Q4 on the schematic.)
- Checked PWM transistors on board. They also fine. (Q2 and Q3 on the schematic.)
- I measured PWM IC's Vcc pin(pin12) and it is 2.4V.
I think, there could be a problem with D12 and D11 but not checked( because they are located under transformer).
Also on this link, the author says this circuit has the self-starting capability. After I read it, I become suspicious of C10 also.
Update1: I checked D12 and D11 both working. I read 110V DC over C10(Input 220V AC)
I attached pictures both front and back.