According to the failure phenomenon, the various main power source of for measuring the output voltage of 0 v, CPU power 5 v output is 0 v. Measurement of the two power supply of 300 v power supply is normal (IC601 respectively 1 foot and IC661 5 feet), and 5 v voltage of the load to ground resistance without exception. According to the principle of CPU power supply control of the main power supply, the judge fault in CPU power, failure may be the cause of the CPU power supply into the working state and then stopped for some reason, this from the flash light and then go out to this phenomenon is obvious. TNY254P (IC662) internal start-up and oscillation circuit, after the 5 feet and 300 v voltage, IC can be automatically entered into a state of oscillation. However, the state of oscillation and voltage control by 4 feet. 4 feet is to make the control side, the external voltage control circuit of the output signal. When the foot for low electricity at ordinary times, through 4 feet within the internal circuit makes TNY254P oscillator vibration. On this basis, the boot instantaneous measure 5 v voltage, the motion of the have a weak moment, confirmed that the analysis is correct. 6UBservice manual download site
 6UBservice manual download site
 6UBservice manual download site
Measuring IC662 4 feet voltage less than 0.01 V. Examine each element regulating circuit, found the photoelectric coupler IC661 resistance between 3 to 4 feet is small, remove the check, confirmed its internal light activated triode C and E are close to breakdown. IC661 model is LTV817M - SM, with a TLP621 substitution, troubleshooting. 6UBservice manual download site
 6UBservice manual download site
1 c661 breakdown, causing IC662 four feet were clamp is located in the low level, in 5 feet get 300 v voltage oscillating circuit after start up, and was forced to stop because of the low level 4 feet, make the CPU power supply, and also can't give priority to the power supply output normal starting voltage, in this case the failure phenomenon.6UBservice manual download site