The iPad Air 2 we are going to fix today was started with water damage
failure, a part of screen got unresponsive. After sending to a repairman, the
screen becomes completely unresponsive, and it was still not fixed well by
another repairman.
After receiving the device, we can see both of
the two white touches were damaged seriously. The iPad boostdiode , black touch and
electric tube had changed, and the touch screen was completely deformed. As
shown in picture 12-7-1 , this white touch is the
least damaged, so we replace the 2 serious damaged white touch first. This
white touch is general with iPhone 6 white touch IC, so we replace it to test on iPad, the failure is still existing. Most
of technicians must know that AIR2's black touch is a common trouble, so we
begin to measure whether the black touch has a boost.
The voltage is only 2.3V on the C4014 when
measured with Fluke 15B+ digital multimer, and there should be a main power supply even if the voltage is not
boosted. Measuring the inductor L4001 we find that the voltage was different.
Taking off the inductor to test, it is the original inductance was burned.
Replacing the inductor L4001, check the diode
D4001 is not damaged, continue to test the device and find that there is still
no boost out, this place should have a boost even if no LCD installed. The
inductor diodes are checked in the three large parts of the boost, only the
black touch itself does not work will cause no boost. The last repairman has
changed the black touch, now we can only change the black touch first. After
changing the black touch, it is still the same as not to boost. so we can
continue to check the working conditions of the black touch, opening
WUXINJI schematic diagram, as shown in picture 12-7-2 .
Both black touch power supply have value: 5.25V
and 1.8V .
The power supply of the 12C bus is normal. As
shown in picture 12-7-3
It is found that the black touch EN signal
comes from the white touch U4150. Is it the replaced white touch problem? Before
replacing the U4150 touch, first checking the U4150 and find there is something
lost, after checking diagram, we get to know it is the resistance U4154.
Through the original factory diagram, it can be
found that the R4154 is the touch clock frequency pull-down resistor. According
to the usual maintenance idea, it is learned that one end of the chip is
grounded, and the pull-down resistor must not drop, similar to the REXT
resistance in iPhone.
A resistance of 4.7K was found on the
iPhone motherboard, and boot to test there is
boosted out, and 18-20V, the iPad screen failure is solved.
It should be that the resistance is lost and
the white touch does not work, the EN signal is not sent to the black touch,
that's why there is no black touch boost.
More professional cell phone repair resources read at www.vipfixphone.com
More professional cell phone repair resources read at www.vipfixphone.com
Its indeed a good post.
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