We got a damaged iPhone 6, the customer
described the failure is cannot turn on. Remove the motherboard
and
connect it to DC power supply, we found that the process of current jump
is normal, which shows that iPhone 6 is not unable to boot, but not display.
The initial judgment of the iPhone 6
motherboard without maintenance, water damaged, fall pieces and so on,
carefully check the display adapter, there is no obvious fault. Now we measure
the data of display adapter (reference schematicdiagram and phone
repair system), the resistance data of display adapter all is normal. As shown
in picture 7-1-1 and 7-1-2.
Then use multimeter to
measure the power supply, it shows +5.7V,-5.7V, the backlight boost circuit is
only about 4V. However, on the normal case, the backlight boost circuit should
have a voltage of about 11-17V. As shown in picture 7-1-3.
Because the backlight boost circuit is not
normal, so we need to check the circuit and find the problem. As shown in
picture 7-1-4,7-1-5,7-1-6.
Working principle and analysis of display screen
1. The machine is powered on 1.8V, through
a small inductor to reach the display screen.
2. The CPU detects the display screen through the MIPI
line.
3. The CPU sends the reset signal to
display screen
4. The display screen sends the power
supply signal to the display screen power supply IC.
5. The CPU outputs the video signal through
the MIPI line, the LCD screen can display.
The backlight power supply is abnormal, but
the +5.7V is normal, this situation is usually caused by damaged backlight IC,
damaged backlight chip peripheral components and backlight IC solder pad
disconnect or virtual welding.
Check the perimeter first with the exclusion
method, finally check the chip. Measure whether the peripheral inductance of
the backlight IC is open or not, whether the resistance has
become larger, and whether the diode breakdown. However, none of this has found
fault. As shown in picture 7-1-7 and 7-1-8.
Then measure the data of each pins on U1502 backlight
drive IC, all is normal. As shown in picture 7-1-9. So we suspect the chip
itself is damaged, replace the new chip.
After measure the voltage of C1503 with
multimeter, it has 16V, which is the normal data. This error repair completes.
As shown in picture 7-1-10, 7-1-11 and 7-1-12.
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