MacBook A1466 no backlight issue repair
Defect Phenomenon: no backlight caused by water damage.
- We can use the flashlight to check the screen to see whether it is with a display or backlight issue
- The water-damaged trace can be found on the motherboard, the water damage indicator sticker also turned red.
Troubleshooting
Clean the motherboard with PCB cleaner thoroughly and check the cosmetics of the motherboard, there is no obvious corrosion, parts missing, or damage.
Then connect the Macbook with the DC power supply and check the backlight working conditions. After measuring, the voltage on the backlight voltage boost circuit is only 8 volts, which is abnormal.
Let’s check the basic working conditions of the boost chip first.
- Chip number: U7701
- Location: near the connector J4400 (shown as below picture)
Measure the below 3 working conditions, all values are OK
- PP3V3_S0 >>> 3V, OK
- PP5V_S0 >>> 5V, OK
- BKL_EN >>> Normal
For the rest working conditions of U7701, as it’s with the BGA package, we can only measure them after removing the chip.
Remove the U7701 and measure the diode values on the PCB
- SW rails: OK
- PWM rail: OK
- FB rail: infinite
Repair Process
FB rail infinite, so the inner rail should be broken, check the bitmap we can jump a wire from pin #5 of the U7701 to a backlight test point as below
Then solder back the U7701 and test, the issue still unresolved. Backlight power supply shorted to ground. We have to teardown the U7701 chip again and check the pads on the PCB to check if there is any tin bridge, but the tin pads on the PCB are OK.
Measure the FB pin diode value on the chip, it’s 0. So the U7701 chip also gets damaged.
We have to replace another new backlight boost IC U7701, then assemble the Macbook to test. After that, the screen backlight is OK and displayed normally
Summary
A1466 820-00165 (2015) no backlight issue get fixed by jumping wire and U7701 IC replacement.
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