The switching power supply adopt STR - S6709 thick-film integrated circuits, check voltage (135 v) + B, boot instantaneous voltage. Then reduced to 0 v. Check the STR - S6709 pet-name ruby foot voltage fluctuations between 5 ~ 8 v (normal 8 v), shows that action of protection circuit. Break operation load, 60 w, 220 v bulb dummy load, boot check + B is 150 v on the high side, but the power can work. Shutdown check on voltage stability control components, no exception. Bootable again, when the measurement with mechanical multimeter 10 v dc voltage stability control light coupling (L9651-81781) (3), (4) feet between voltage, found that the load lamp brightness to reduce. Doubt there is something wrong with the light coupling, its performance good TLP621 substitution after troubleshooting. NqTservice manual download site
 NqTservice manual download site
 NqTservice manual download site
It is worth noting that the fault light coupling to replace the multimeter to resistance test did not see abnormalities. To investigate its reason, by experiment circuit for testing. It is found that its control characteristic significantly worse.NqTservice manual download site