Observe different is compared with other power failure power thick film blocks IC801 has burst, at the same time, D825, D823, R809, R810 damage. According to the fault phenomena analysis, it's certainly not the current breakdown, is a typical voltage breakdown. Can be concluded that is a certain element in the detection circuit itself bidirectional thyristor Q801 breakdown or damage. Through inspection found that the bidirectional thyristor Q801 has breakdown conduction, Q853, Q854 also lost the switch function, so as to make the doubler rectifier circuit. At this point, the rectifier filter circuit and voltage doubling rectifying filter circuit work at the same time, the superposition of two output voltage, the 600 v voltage to power thick film blocks IC801, burst. Mentioned earlier detection circuit and the bidirectional thyristor Q801 in 220 v power supply situation, somewhat redundant. Since our country is 220 v power supply, so we can completely remove the testing circuit and Q801, only keep bridge rectifier circuit is ok. After remove the detection circuit and Q801, change IC801 and D823, D825, R809, R810 commissioning, machine back to normal.UZ3service manual download site