Hitachi NP82 machine adopts the series wide type switching power supply, switching power supply output, + 111 v voltage for output circuit, audio power amplifier circuit, also for line and line, field scanning oscillation series power supply. Line output work, providing field output 55 v power supply, 12 v power supply for small signal processing circuit. So when the power supply circuit, scanning circuit and the 12 v voltage regulator is out of order, are there will be no grating, no audio fault. cW2service manual download site
This machine also has a protection circuit, when the switch power supply output voltage, output pipe line current increase, line flyback pulse voltage rises, all can cause a protection circuit action, no grating, no audio fault. But protect circuit of grating, sound at the same time, the power switch transformer have a "make" cries. cW2service manual download site
When the protection circuit itself is out of order, cause the protection circuit misoperation. Also can produce the failure phenomenon. cW2service manual download site
(1) the first check boot C906 on both ends of the voltage is 300 v, explain the power rectifier, filter circuit works well, switching power supply has no short circuit flow phenomenon. cW2service manual download site
(2) the switch power supply output measurement C909 + B voltage of 0 v, switch transformer without "toki cheep" quack, switching power supply does not work. cW2service manual download site
(3) will launch a capacitance C912 short circuit, forcing start, still to 0 v + B voltage, transformer is not a "squeak" cries, switching power supply is still not oscillation, failure in the switch power supply circuit. cW2service manual download site
(4) check the thick diaphragm IC901 surrounding components: D906, D908, D905, C908 are intact. Remove IC901 measure resistance between each foot, found that (1) and (2), (4), (2) the feet and are up to the resistance, indicate that the switching power supply has open circuit within IC901, so can't start. cW2service manual download site
Replace the new STR6020 machine back to normal.cW2service manual download site