According to the light, green light and then go out into the red, preliminary judgment switching power supply and line scan circuit has work, and then enter into the state of protection. Use measuring point voltage, judge fault range, measuring voltage + B first, boot instantaneous voltage 140 V, then K801 disconnect, + B to 0 V. Measuring various fracture in microprocessor protection circuit trigger voltage and voltage, found Q856 boot moments have a sudden rise in voltage of 0.5 V, the microprocessor IC1213 6 feet for high level at the same time, the judgment is associated with Q856 the base of fault detection circuit protection. dwgservice manual download site
 dwgservice manual download site
 dwgservice manual download site
On line measuring output has no obvious under the condition of short circuit, adopt measures from fault detection circuit, remove protection method, individually disconnected and connected Q856 fault detection circuit, when disconnect IC451 boot no longer protection, but the grating appeared a bright line, which is field scanning circuit failure, caused by the protection. To test the field scanning output circuit, found that the output of the IC451 internal breakdown with the power supply (3) (2) the feet. dwgservice manual download site
 dwgservice manual download site
After replacement IC451, restore protection circuit, boot is still after the green light is shining once, become red. Check again for protecting circuit, or disconnect after IC451, boot appeared a level bright line, inspection on field output circuit, again found near field output capacitance C454 circuit board with the electrolyte flow, resistance R454, R462 charred traces. So the judge C454 leakage R454, R462 scorch, led to a higher output voltage, protection. After replacing C454, R454, R462, boot grating back to normal again, no longer protect, troubleshooting.dwgservice manual download site