For the measurement of a switching power supply output voltage + B standby 33 v normal, remote boot after + B voltage up to 130 v, all is normal; Automatic shutdown + B when the voltage rise suddenly, then the lights go out, a + B voltage drop to 0 v. Judgment is an individual element thermal stability is bad, cause current or voltage change after heating, vibration or switch power supply shutdown caused by: P9gservice manual download site
 P9gservice manual download site
2 it is poor contact power supply circuit, heated welding stop working. P9gservice manual download site
 P9gservice manual download site
Testing did not see obvious carefully for the power circuit open welding phenomenon, open for possible welding solder joints after repair welding, the fault is still, the poor thermal stability of components may occur heating test, also did not find out the problems. P9gservice manual download site
 P9gservice manual download site
Automatic shutdown of the moment, the measurement of silicon controlled rectifier control voltage by the normal 0 V suddenly rose to 0.7 V, so the machine into protection state. Observe the machine fault, the normal watch, light to orange + B output voltage is 130 v. Standby indicator light is red, the output voltage + B to 33 v. Automatic shutdown, the output voltage to 0 v, the lights go out, further judgment is thyristor Q7991 into protection state. One is to protect the circuit element thermal stability is poor, after heated metamorphism caused protection: the second is to protect the circuit detecting a change in the current, voltage across the protection setting value, the protection circuit starts. P9gservice manual download site
 P9gservice manual download site
Because of the control of the thyristor Q7991 extremely external protection circuit is more, in order to see the real failure phenomenon, adopt the method of remove protection, disconnect R970, cut off Q7991 connected with the photoelectric coupler IC902, boot to watch. Just boot, all normal, images, audio, grating detection switch power supply output voltage are normal; After 30 min, image when the twist, and gradually become out of sync, line output transformer at the same time issued a "creak"

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