1) Symptom Recognition
2) Symptom Elaboration
3) List Probable Faulty Functions
4) Localize the Faulty Function
5) Localize the Faulty Component
6) Failure Analysis
7) Retest
And before the half-split where you check goz-intos and goz-outos, verify that the power supply is putting out the correct voltage and doesn't drop out on loading. I've seen a power inverter give the correct voltage on the output unloaded. And when it was lightly loaded, the voltage went to zero.