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4Kmservice manual download site
Five, the overhaul, protection circuit will still Q804 removed, in the case of using light bulbs as load, the following key points: (1) voltage electricity detection photoelectric coupler D836 diode side (1) the foot, normal about 1 v. Abnormal should check R849, D812 and 16 v power supply circuit. (2) the photoelectric coupler D811 diode side (1) the foot, normal about 1 v. Abnormal should check R864, Q805, D831 circuit and a + B pressure. (3) the photoelectric coupler D836 (3) (4), the voltage of the transistor side, normal should be close to 0 v. If the voltage is greater than 0.5 V, C838 can determine D811 photoelectric coupler internal damage of open circuit (D811 damage rate is higher in practical maintenance). (4) Q804 base of less than 0 v when the voltage is normal. If more than 0.5 V, usually Q827 damage. You should also check C824 anode voltage, normal should be 8.1 V or so. If too high, it may be D836 open circuit damage. The voltage is too high, because C824 may directly Q826ce breakdown, the protection circuit. Each key point voltage, attention should be paid to separate hot and cold. Protection circuit maintenance, Q804 access circuit, restore protection function. 60 w bulb, turning on the power supply should be quickly lit, remote control, normal power. D832 access circuit, protection circuit can be controlled, once again, turning on the power supply light bulbs should not light up. Otherwise, should be examined Q831, Q805 and peripheral circuit. 4Kmservice manual download site
After switching power supply to work properly, remove the light bulb, will R834, R835 access circuit, restore its protection function. If, after electrify lights flashing out, that failure is a good field scanning parts, then to repair the part line, field scanning. 4Kmservice manual download site
Maintenance example 1: a panasonic TC - 2188 - s color TV boot 3 without, light is not bright. After application of the above methods for maintenance, remove protection circuit, single fix a switching circuit part, found not lit, 60 w bulb in can use 25 w bulb light, + B measuring voltage is normal, but open after the switch to be light bulb has delay time of 2 seconds. Judged as IC802 aging, 0.022 mu in parallel on C811 polyester capacitor, 60 w bulb can quickly lit, circuit work normally. After Q804 access circuit, light bulb can't light, concluded that the abnormal protection circuit work. After will take off, Q804 points measuring voltage, found C838 desperately voltage is above 5 v, Q804 base in more than 4 v. Results found D811 light coupling triode side open-circuit damage, Q827 emitter junction damage. After the above components in new, troubleshooting. Try to 0.022 mu capacitance shunting on C811 get off, can see the boot, not practice results.
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