The investigation fuse intact, but each output voltage of the power supply are standby value, the input voltage IC804 is approximately 2V. Normal, the Q802, Q803 standby power switching circuit composed work , provided by B4 approximately 13V voltage through R833, Q802 IC804 applied to the input , thus ensuring IC804 still in standby +5 V output for CPU. Thus , the standby power switching circuit does not work . In this part of the inspection, found that R833 (22Ω) open, the machine returns to normal after replacing the R833.5pRservice manual download site

Overhaul of such failure to pay attention to the following points : ( 1 ) this case, some inexperienced beginners often mistaken for load short-circuit or power regulator control aspects of anomalies, leaving the maintenance astray. To prevent false positives , you can disconnect the input of IC804 , using an external +15 V power supply for the IC804 . If the power supply output voltage is normal , and can normally watch , then focus on maintenance standby power switching circuit ; On the contrary , you should repair the power supply or the load. (2 ) an open resistor R833 , Q802 e still in a very measured voltage of about 20V , then easily misjudge R833 leaving normal maintenance trouble. I am confused about this phenomenon : since R833 is open, why can the Q802 's e very measured voltage of about 20V .5pRservice manual download site