By resistance measurement method to detect the output of the power supply and the brightest no obvious short-circuit fault on the ground, and then using force boot method, disconnect Q805c pole and connected D825 (note should also be disconnected D837, D830 and D825 of connection), then the dummy load measurement + B voltage is 115V normal; remove the dummy load, recovery line scan circuit is energized again found grating as a horizontal bright line, after the repair and replacement field output circuits, power is still protected. Overhaul of the field circuit, found resistance field sampling resistor R476 overcurrent protection circuit becomes larger, the 1.2Ω normal increases to 5Ω, when the field is estimated to be output circuit malfunction charred, resistance becomes larger cause error protection. After replacing the R476, troubleshooting.8Edservice manual download site