Panasonic TC-29V30H-TV, cold booting can work for half an hour or so, the heat engine 5 to 10 minutes automatic shutdown, and in the instant before the shutdown, the screen brightness dimmed fault rep -Service Manual Download|Circuit Download|Download Drawings|schematic download|route map download|free download user manual

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Panasonic TC-29V30H-TV, cold booting can work for half an hour or so, the heat engine 5 to 10 minutes automatic shutdown, and in the instant before the shutdown, the screen brightness dimmed fault rep

Time：2014-05-23 15:40:31 Source：Network Author：Unknown Clicks：1273

From the analysis of the failure phenomenon , is a component poor thermal stability, protection circuit caused due . The machine has a variety of protection features current, overvoltage , undervoltage . Partial protection circuit ( see figure ) .7MCservice manual download site
7MCservice manual download site
When the pressure drop increases 140V overcurrent on R827. This voltage is applied through R828 Q806 base , so Q806 is turned on ( actually lower base potential ) , resulting in D potential rise . So Q554, Q555 have been turned on. 5V voltage through Q555, R566, D560 added to the base of Q841 , Q841 optocoupler make the photodiodes have been turned on. Resulting in Q803 base potential rises saturated conduction . Cause C804 positive potential is almost zero , the power switch Q801 stop oscillating.7MCservice manual download site

When 140V overvoltage make R835, R836 on increasing the pressure drop , D843 breakdown, the SCR is triggered Q821 turned on and the base potential of Q820 Q820 is decreased by conduction. 5V voltage through R833 added to point D , so that the point potential rise , resulting in protection circuit .7MCservice manual download site

Similarly , when the 140V undervoltage , Q894 base potential drop , so he turned on the tube . 12V voltage through R897 makes Q841b pole potential rise , causing the tube conduction. From the previous analysis shows , Q801 will stop ringing. In addition , 12V overcurrent, output overcurrent field , the second anode voltage is too high (X-ray excess ) ( electrical schematic not shown) will cause the D point potential rise , resulting in protection circuit .7MCservice manual download site

The aircraft normally D point potential of about 0.2V, the voltage drop on the R827 is about 0.3V. In the moments before the shutdown , the measured voltage drop on the R827 increases as high as last 0.8V, instructions are overcurrent protection. The main load is a 140V line output circuit . Since the brightness dimmed before shutdown phenomenon , indicating high pressure decreases, so the focus suspected output tubes, flyback capacitor soft breakdown. Invalid check with the substitution . Hand touch line output transformer fever, suspected that thermal breakdown voltage silicon stack , resulting in high-voltage short circuit. After replacing the line output transformer troubleshooting.

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