LG rear projection TV RT44A84R screen flashing black screen fault repair example - android - Phones Developers

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Second, LG rear projection TV RT44A84R one, description screen flashing, black screen. Disassemble the machine and find that the small signal board is all cooling oil. Remove the projection tube assembly and carefully check the G tube for oil leakage. Disassemble the cover, use the syringe to extract the cooling oil, remove the lens projection tube, and put the sealant for the car engine on the original gasket. Press the screw. Pour in the cooling oil. At this point, the oil is repaired.
Remove the small signal board, wash it with banana water, blow dry, wash it, and then dry it. Install the projection tube and install the signal board. Check it correctly and turn it on. Screen characters are scattered and jittery. I soon smelled a gum. Frightened, immediately shut down, carefully check, found the convergence board, the power supply resistor burned. After measuring it for a while, I suspect that the signal board has not been washed and blown clean. Rewash N times, the upper plate, the fault is enlarged, the convergence resistance is red, the filament is bright, and there is no grating. Remove the plate and blow it again, then wash it. After several weeks of demolition, no results. Change the idea, no longer wash the board, remove the convergence board, the measuring tube is bright, the voltage of the measuring field block is normal, and the retrace line appears on the convergence box screen. The line scan circuit is normal. The power supply of the small signal board is normal, and R, G, and B are measured. The 3.7V is normal, and the 12V power supply of the tailgate is only 2.1V. Run the line, the power supply is regulated by 14V IC PQ12RD21, check the IC is 2A, 12V four-terminal voltage regulator, 1 pin output 2 feet 3 feet input, 4 foot control feet are empty. Test 1 pin 2.1V output, measure 3 pin 3.0V input. The video is disconnected and the voltage is still measured. At the 3rd foot, the line runs back to 14V. Turn the board over and measure the B side to 14V, dizzy! The hole A to the B side of the through hole are measured, and a total of 4 through holes are leaked out of the cooling oil to open the way. Wires A and B are also connected. On the machine test, characters appear. Replace the power supply resistor of the convergence board and install the convergence board. Boot into convergence mode, RGB all misplaced. Adjust the deflection magnetic ring and correct most of them. Then use the remote control box to fine tune and connect the signal normally. This machine is fixed. Since the 14V line is turned on, the viewing and discharging work is abnormal, and the 14V also supplies power to the convergence control circuit. Therefore, the abnormal operation of the convergence circuit causes the current of the convergence block to be too large, and the fuse is burned.