iPad Air shows high current when power on and motherboard chip is hot

Trouble Phenomenon

When testing with display, DC power shows high current and power management chip is hot.

Repair Process

This iPad Air has been fixed once. After teardown, we find ipad battery and LCD flat cable are stuck with insulating tape. Teardown motherboard, measure the diode data of the battery power supply pin and of PP_VCC_MAIN voltage. The data is normal. Test when connecting adjustable power supply and use tweezers to short connect power on pin. DC power displays the current changes and iPad can be turned on normally. Connect display screen to do further test and short connect power on pin. DC power displays the current changes normally, but the current suddenly rises when display screen is about to be bright. At the same time, the power management chip is hot.

Immediately remove ipad display screen and assemble it to a fine motherboard. It displays normally. Therefore, we conclude the problem happens on motherboard. Measure motherboard display screen interface and find the diode data of the pins of backlight power supply PPLED_BACK_REG_A and PPLED_BACK_REG_B is infinite. We can be sure that the backlight circuit is open. Picture 2-22

Measure the power supply inductor L4680 and L4685 near the interface and they are normal. Picture 2-23

Measure two diodes D8428 and D8458 connected with the above inductors (picture 2-24). They are burnt out, as shown in picture 2-25. Replace the two diodes and connect the display screen to test. The screen displays normally. Trouble is removed.

Picture 2-24 and Picture 2-25.