Maintenance Changhong LCD TV LT3712 LS10 movement machine fault is weird, each time the AC boot black screen, the backlight is bright, there is sound, the remote control is turned off, then the remote control is turned on twice, everything is normal.
First of all, suspect the power failure, replace it with the Changhong GP03 power supply with standby maintenance, the fault remains, and the power failure is eliminated.
When the fault is detected, the LVDS signal waveform of the motherboard to the logic board is completely absent, which is obviously the fault of the motherboard LVDS output block 5151.
When the fault is detected, the 5151 large block power supply is normal, the crystal oscillator waveform is normal, the reset is normal, and even a forced reset is performed, and the fault remains. Do not understand, the limited time during the day, only have to take home to repair.
Connect the circuit board at home and input the color bar signal. The output of the 5151 LVDS signal is very normal. It is suspected that there is a virtual soldering phenomenon and repair welding.
On the second day, the machine was tested, the fault remained, and the high-voltage board was unplugged. The logic board was tested separately. The fault remained. It had to be brought back and checked carefully. Unexpectedly, the home was still normal. Is it because the temperature is different and the fault occurs?
The test machine in the store, or the fault is still the same, had to be carefully checked, this time found that the LVDS cable of the logic board was removed, the fault disappeared. Note: At this time, the LVDS waveform measured by the oscilloscope is judged to be normal.
Is there a problem with the logic board? In the fault, the voltage of each logic board is measured. It is suspected that the load capacity of the LVDS driver block 5151 is poor. There are only two factors, the block itself is bad, and then the power supply is bad. Remember to measure the power supply of the block 5151. Is it starting? Is there a drop in the instantaneous power supply? With the suspicious measurement AC power supply motherboard power supply 5V power supply, and found the problem, there is a momentary drop phenomenon, this time found that the power supply is different from the DP03 power supply made by Changhong, standby 5V and the motherboard work 5V belong to the same group of power supply, by the standby control board Work 5V output instead of the usual stand-alone 5V standby power supply.
Try to use the short reception machine 5V and the motherboard to work 5V power, the boot failure disappears.
This machine repairs a lot of trouble, in fact, in the first maintenance, the logic board was disconnected, and the cancellation of the standby circuit did not make the fault disappear. .
Attach a photo of the repair. .
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