By understanding the user, thunder and lightning from power supply. Visual check cracking power thick film circuit, the fuse black F801 fusing, resistance R802 open circuit, rectifier bridge D806 in two diode breakdown, photoelectric coupler D803 {1}, {2} feet open, after the replacement of damaged components above, break operation output circuit, the a + B output termination 60 w bulb false load of commissioning, and voltage monitoring + B. After startup, the light bulb brightness twinkle change, + B voltage instability. Analysis of voltage regulator or a fault protection circuit. Check the voltage loop, no exception, and then check the protection circuit. With perfect protection circuit is more complicated, with over voltage, over current, short circuit protection function. The circuit consists of Q831, Q805 over-current detection circuit, D837, D830 load short circuit detecting circuit, D831 overvoltage detection circuit and optical coupling D811, Q827, Q826, Q804 composition. When normal D811 by 16 v power supply via R864, D825 power supply, point B for high potential, D811 internal light-emitting tube, transistor saturation conduction, A point of low potential, Q827, Q826, Q804 cut-off, impact on thick film circuit internal switch tube. When the over current, over voltage, short circuit detection circuit gesture, point B to low potential, deadlines, point A is A high potential, D811 Q827, Q826, Q804 conduction, thick film circuit switch tube in extremely short circuit oscillation stop B. When disconnect Q804 c extremely, returned to normal power supply output voltage, fault indeed as expected in the protection circuit. Q827 in the protection circuit and Q826 analog silicon controlled rectifier circuit, once in the protection state, in the case of constant electric cannot protect the exit status, and the machine dummy load bulb bright and dark change, an analog silicon controlled rectifier circuit fault, check the analog silicon controlled rectifier circuit, found D823 open, D811 {3}, {4} feet open circuit. Replace after D823, D811, no longer flashing brightness changes, the output voltage is stable at 110 v. Remove the dummy load, output circuit, troubleshooting.

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