The machine after startup, measuring about + B voltage of 70 v. Measured again add dummy load operation of power supply, + B still about 70 v voltage, switching power supply is faulty. The output voltage 70 v, the power supply has the vibration, the fault should be in the pulse width control circuit or voltage control circuit. Doubt positive feedback circuit has a problem, check R905 resistance value is correct, replace C910, fault, still check diode D905, forward resistance. After replacing D905, fault disappear.6RRservice manual download site