Hitachi CPT - 2117 color TV, sometimes to boot, sometimes can't boot. Can't boot the power indicator light is not bright, repeatedly press the power switch, or electricity for a few minutes later, sometimes can start; As long as you can boot, you can watch normally, and has been normal. 3h4service manual download site
 3h4service manual download site
Measuring C906 + 300 V voltage is normal, measuring + B filter capacitance C909 no + 115 V voltage at both ends. Check the start of the switch power supply, feedback circuit components are no exception, suspected of switch power supply circuit welding, all all solder joints may open welding repair welding, boot back to normal, thought to repair. But the next day, boot difficult fault occurring again, again measured C909 + B at the ends of the voltage, found 10 volts, turning the moment then to Ov, so switching power supply has been started, and then stop. Start doubt protection circuit, measuring Q902 G voltage control, indeed as expected for 0.7 V, the state of protection. 3h4service manual download site
 3h4service manual download site
Using lifting line output over-current, over-voltage protection, the method of boot measurement switch power supply output voltage of + B is normal, sound, light, all normal, ruled out the line switch power supply output voltage and the output over-current, over-voltage protection, judge fault is caused by the error detection circuit protection. But for fault detection circuit, zener diode detection of partial pressure resistance, no exception; Measuring various zener diode cathode voltage detection circuit, these people are no more than zener diode voltage value, make the maintenance was in trouble. 3h4service manual download site
 3h4service manual download site
Later, consider just boot is not activated, after preheating can sometimes start, conform to the fault characteristics of electrolytic capacitor, electrolytic capacitor capacity of suspected protection circuit is reduced, cause boot error protection, capacity increase after preheating, exit protection by mistake. Restore protection circuit, respectively with 10 u F / 50 V capacitor parallel C913, C753, C755 boot test, when parallel C913, boot protection, no longer doubt C913 capacity decreases. After replacement of C913, fault completely ruled out.

 2    1 2 Next Last