According to the symptom analysis, power led is not lit, indicating abnormal DC circuit. Bridge rectifier output logging, but pressure drop fluctuations. Shutdown, switches under static test is normal, normal; this type of monitor is equipped with overcurrent (or pressure) protection device when an exception is line scanning circuits output, supply voltages +110V measured to determine line scanning circuit "overloads" phenomenon; test output circuit with a multimeter, test found damper diode has been penetrated, forming pathways. After the replacement, troubleshooting.