First remove the F803 at 100W 115V voltage output access dummy load , while removing the power supply circuit VQ820, VQ821, VQ825, VQ832, VQ828 five transistor, measuring the output of 115V power voltage is normal . Its manifestations have two : one , the output terminal voltage at this time is normal , that is, these circuit protection circuit fault caused the output voltage becomes abnormal . Then one by one each recovery protection circuit , VQ820, VQ821 must be restored to the way while , VQ828 standby and power control circuit ; VQ825 to switch protection circuit ; VQ832 as over-voltage protection circuit. Each recovery test once all the way on the power output of the voltage , if the output voltage when the recovery which abnormal failure can be determined for the road , you can carefully check its peripheral circuits. 2 , the output voltage is still abnormal , it has nothing to do with the protection circuit above , should be sampled and regulation loop problem. Recover more than five transistors, focus on examination VQ822, VQ824, VQ87, NQ826, NQ829 its peripheral circuits. Another switch control circuit failure can also cause this failure occurs, the main check VQ841, VQ842, VQ831, VQ834.

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