Yesterday, we received an iPhone 6S, which problem is the iPhone home button often gets unresponsive, and it will automatically change to recovery mode. Now, we need to fix it.
Disassemble the iPhone, and take out the motherboard, we found that the CPU and WiFi has been repaired, 32.768, 24M, iPhone NAND flash were also replaced.
Measure the iPhone motherboard with
multimeter, power-on current is normal, then install the assembly
to test, all of functions are normal, so we put aside to charge. An hour later,
we find that home button has no response by pressing several times. The iPhone
device could be lighted by pressing the screen-lock button, but home buttion is
responsive after screen is locked, so the fault was judged as wake-up delay.
Measure BURRON_MENU_KEY_CONN_L, the home button voltage is about 1.3V as
normal valure, considering the peer has changed the
iPhone WiFi, clock, CPU, so the
fault is locked in the fingerprint button scale. The original picture is shown
in picture 1.
According to observe on the picture, we get to know the board is without
print, we doubt the iPhone 6S CPU has
been doing the real-time test to whole device hardwares after booting, this
motherboard has no original fingerprint key. Fingerprint key does not match, so
it's suspicious that the CPU has been repeatedly verify if the fingerprint key
is matched, which leads to wake-up delay, standby sleep phenomenon.
Next, we're going to disconnect the fingerprint so that it doesn't work. As
shown in picture 9-8-3 . After disconnection, the
phenomenon of delayed wake-up disappears. We test again before shipping it back
to customer, it cannot be turned on now, measure the current with 70 Ma,
connect it to the computer, which displays recovery mode, but does not display
the model. As shown in picture 2.
It cannot identify the model, we find the resistance on phone circuit diagram and measure whether the pull-up
voltage is normal, the result is only 1.65V.
Remove a 240 ohm resistor from the scrap motherboard to change the pull up
voltage.
Finally, we replace the 240 ohm resistor, and then we power on iPhone, it boot smoothly now. The iPhone can back to work.
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