Yesterday afternoon, I was invited to repair a Hisense 52 LCD TV. I have already opened the TV to the user's home. The screws are not fully installed! Listening to the user's description is that there is a blue screen at boot, and it is necessary to turn off the power several times before there is an image, no sound, and the TV has been repaired after the sale. Disassemble the TV and watch the things inside. The power test machine displays the blue screen after the Hisense icon. Pressing the remote control button has no response. The same is true when the button is unplugged. The power supply is not abnormal. Seeing that it is more troublesome to repair, others have repaired to say to the user to pull the TV back to repair, first repair the board, repair the bad and then change the board, report the two price users to agree to pull the TV back!
After eating the afternoon meal, I started to overhaul, but the fault phenomenon after power-on has been different from the user's home! At this point, the TV will turn off and the TV will automatically shut down and then turn it on again, then keep cycling! Measuring 5V 12V and 24V has also been normal, check the motherboard's regulated output 1.8V and 3.3V is no problem, so write the next data, the backlight can always be bright when writing data, the fault phenomenon is still the same after writing!
Then, according to the user's repeated switching of the TV to the image, the sound is not, there are some red snowflakes on the viewing image; suspected that the power supply has interference, the digital meter is hit to the HZ when the power output is output and the voltage regulator output on the motherboard is also No problems were found.
As time goes by, you can faintly hear the sound, and the repair is still not progressing! Is it really necessary to change the board? Checked the disassemble motherboard is also above 200, think of the oscilloscope oscilloscope function has not been used, find out the instructions to use on this TV, test the 1.8V 3.3V and 1.3V power supply waveform on the motherboard, 1.3 The V waveform is significantly thicker than 1.8 and 3.3V; looking at the circuit going to 1.3V is to supply power to the main chip, so the C821 16V470UF capacitor on this circuit is removed, but the capacitance measurement is normal! Anyway, I have already taken it off and decided to temporarily install a new capacitor. Try it out immediately! It should be it! The wave measurement type is also normal, 1.3V has also become 1.2V! Turn off the TV and open the door to enter the room with cold air and then turn on the TV. Watching the watch has been more than 10 o'clock, you can sleep!
The next morning, the test machine is also normal, call the user to determine the repair cost and reset the capacitor! TV is sent to the test machine for normal charges!
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