The multimeter test mu PDT533CU - 266 boot reset signal level change, and measured the CPU can protect the port has been in a low level state, the CPU internal basic normal, this can be the fault range narrowed to power supply, voltage regulator and filter circuit. Use plus a + 5 v power supply of commissioning, first observed two hours did not happen this problem. Check the bridge rectifier, a three-terminal voltage regulator of LM7805 and C203 ~ C206 capacitors are no exception, so the judge fault in power transformer primary side before. Due to the circuit in the power transformer with a combination of four temperature protector, respectively is used to protect the fan motor, printed circuit board, terminal board and electrical product box, one by one check, found that the fan motor protector (109 ℃) near connectors have black oxidation phenomenon, plug-in is loose. After cleaning, plastic, electricity of commissioning, fault completely ruled out.VSnservice manual download site