Fault
phenomenon
The customer has repaired the WiFi fault
and camera circuit, the camera 2.85V Camera FlashControl IC U2301 has been replaced,
the fingerprint cannot be entered, as shown in picture 4-7-1.
Repair
process
According to the customer's description, Camera
Flash Control IC U2301 has been repaired, because the position of U2301 and
fingerprint power supply IC U2100 is close next to each other. After the check,
we found that U2100 is slightly damaged, so we are determined to remove one
from the motherboard, soldering Tin ball and reinstall to failure board, then boot and
test it, but the fault is still the same. Next, we start to measure the output
pin A2 pin of power supply conversion IC U2100 with multimeter, see if it has 1.8V voltage output, find the peripheral capacitance
C2181 and test it; we found that it could measure to 1.8V.
The picture of the fingerprint power
conversion chip U2100 replacement is as follows, 4-7-2
Based on the above measurements, the power
supply is normal, which means the U2100 circuit is installed. According to the
principle, now we only can measure the diode data of J2118 pin on the
motherboard first, after measurement, we found that the diode data of sixth pin
on J2118 is infinity, which shows there is a disconnect between this line and
fingerprint boost chip. Check it in the schematic diagram, we know that there is a inductance from sixth pin of J2118 to
fingerprint boost IC U1503, we can found the diode data on first pin of
inductance.
The conclusion is that the inductance
FL2156 is inveracious soldering or damaged. Put it under the microscope, and remove the black
glue around the FL2156, paint the UV solder flux and then solder it with soldering station, as shown in picture 4-7-3. Once again to measure the diode data of
sixth pin on J2118 adapter, the data is no longer infinitely large. Turn on
iPhone and test it, the fingerprint can be entered normally, as shown in
picture 4-7-4.
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