Laptop Model : Lenovo B470
Motherboard number: A47 MB 10250-2 Independent Graphics
Fault Description:
The screen flashes when the Laptop
is turned on and displays the logo, and also flashes when entering the system
welcome interface (there are traces of water intrusion, but the machine can be
turned on, and it is speechless).
Maintenance process:
It should be a backlight
turning on failure. After quickly disassembling the machine, there were
traces of water corrosion, but it did not affect the Laptop operation. After
scrubbing the motherboard, the fault persisted.
Use an oscilloscope and turn on
the signal with the backlight of the screen capture line. When you see the
waveform in the picture below, you can clearly see the signal fluctuations.
Check the signal source, it comes from EC
control. To be honest, I haven’t really studied the cause in depth, so I
just changed the wiring: the screen backlight turn-on signal directly pulls the
screen power supply turn-on signal.
In order to prevent the white screen phenomenon at the moment of booting, the screen power supply is directly skipped and the U4901 chip is short-circuited to the 3V voltage of S0, and the repair is completed.
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