②. Measure whether the voltage at the output end of the power factor correction circuit is normal or not.

③ measure whether the voltage of 15v sb at the output end of the auxiliary switching power supply circuit is normal.

④ measure whether the on/standby control voltage is normal and whether the standby control transistor and other circuit elements

are normal.

⑤. After the above inspection, the power supply circuit is restored to normal. If the power-on test machine is still not working, then measure whether the output terminal voltage of all DC-DC voltage conversion chips on the motherboard is normal. If it is abnormal, just check the components around the abnormal pins of the chips.