Observe the mechanical and electrical source light is not bright, power supply circuit didn't work. Teardown check found, this machine structure is relatively complex, the whole machine by the size of 13 independent circuit board through socket connection. Only ac filter, ac rectifier, 220 v / 110 v conversion circuit is to use two pieces of independent circuit board. Visual inspection, the exchange insurance tube in good condition, rectifier circuit not seen obvious damage, + 300 v rectifier output voltage is normal. qVYservice manual download site
 qVYservice manual download site
Preliminary concluded that fault should be in standby control circuit. qVYservice manual download site
 qVYservice manual download site
Refer to relevant information, after the machine belong to panasonic M16 machine core, the power supply circuit is more special, used a similar power supply way of computer power supply), that consists of a main and an auxiliary switch power supply of switch power supply, auxiliary switch power supply or standby power supply. Judging from the power indicator not on this phenomenon, this machine fault should be the standby power supply does not work. Standby power supply circuit as shown in the appended drawings. qVYservice manual download site
 qVYservice manual download site
 qVYservice manual download site
By the figure can be seen, from the output of the rectifier circuit + 300 v power supply is divided into two road: a path connector N7, D7 (1) the direct supply main switch power supply circuit, the other path resistance R883 standby switch power supply circuit. Standby switch power supply is not controlled switching power supply (once you press the power switch on the front panel, connect the ac power, standby power supply into working state), its working principle is as follows: + 300 v from the rectifier filter circuit after resistance R883 output of about 280 v dc voltage by the connector N7, D7 (2) the end connections are divided into two after the road: qVYservice manual download site
 qVYservice manual download site
T881 (5), (4) a path switching transformer winding is added to the switch tube 0881 collector; Another path to start resistance R881, R882 to switch tube Q881 base, provide Q881 starting current, make the Q881 conduction, Q881 collector current through the switch of the transformer windings T881 (5), (4), (2), (3) in between winding induced voltage, the voltage via C883, R883 fork to Q881 base, the formation of strong positive feedback, saturated conductivity 0881 quickly into the state. As the capacitance C883 charging end, Q881 base potential began to decline, will eventually make Q881 exit the saturation state. At the same time, during the period of 0881 into the saturated conductivity, the ends of the emitter resistor R885 that 0881 will produce a linear increase of voltage, the voltage is greater than 1.4 V, D820, Q882 conduction, at the same time make Q881 base of conduction, independent power supply starting current and positive feedback from the switch transformer (2), (3) winding current flow to the ground, also can make 0881 out of saturation on state. When Q881 exit the saturation state, T881 (5), (4) the current in winding is reduced and generate reverse induction electromotive force, the T881 coupling, between (2), (3) winding induction (2) negative, and (3) positive voltage, (2) the negative voltage via C883, R883 feedback to Q881 base, make Q881 rapid transition to the off state. Because of Q881 cut-off at the same time, its no voltage on both ends of the emitter resistance R885, D820, Q882 deadline at the same time, return to the original state. So, produce the intermittent oscillation. After the construction of the oscillation, switch the pulse voltage transformer (1) end after D882 rectifier, C881 filtering on D885 form 16.8 V voltage, mainly by R886 circuit provides standby control switch power supply voltage; 6, 7) causes the pulse voltage by D886 rectifier, C885 filtering, formation of about 8.5 V dc voltage: all the way to mute control circuit, a path IC803 voltage output stable after 5 V voltage of the power indicator light, microprocessor, memory, and boot reset standby provide standby voltage control circuit. Add IC803 electrical test (3) feet without 5 v voltage output, measured (1) feet no voltage input. Measuring Q881 collector voltage 280 v, but the base voltage is zero. Power measurement Q881 each electrode resistance is normal, emitter resistor is normal; This phenomenon shows that Q882 has breakdown or fully conduction, will lead to Q881 base and ground conduction resulting in auxiliary power oscillation stop. Removed 0882 measuring the electrode resistance, normal D820, C886 is normal, when the measurement to D885 found D885 breakdown short circuit. Because you don't have 16.8 V voltage regulator tube, then using a 12 V voltage regulator tube with a 5 V voltage regulator tube series after replace D885, charging of commissioning, the power indicator light is lit, measuring the output voltage of 16.8 V is low (15.3 V), slightly IC803 output of 5 V voltage is normal, and the signal of commissioning, everything is normal, the fault machine repair.

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