Reparación del MacBook A1502 sin pantalla

MacBook A1502 no display issue repair.

Modelo: A1502

Junta No: J44 820-3476

Fenómeno del defecto

No display

Proceso de reparación

Connect the MacBook and boot it up with the DC power supply, the trigger boot current is 0.15A only which is abnormal. 

Detach the motherboard and find the motherboard was water damaged before, and the customer has cleaned it before. The cosmetic of the motherboard looks fine, there’s no obvious component corrosive or damage.

Then connect the motherboard with the DC power supply machine again, and measure the below voltage values on the relative inductors.

• =PPBUS_G3H
• =PP5V_S4
• =PP3V3_S5
• =PP1V05_S0

The voltage values are normal, but there’s no voltage for DDR on the =PPDDR_S and has no power supply for the CPU either. Disconnect the DC power supply and measure the diode value, the diode values are all OK.

Let’s start with the DDR power supply PPDDR_S3. 

As we can see from the schematic, below is the power supply for the DDR

After measuring, cannot measure the voltage on the Pin 16 (the DDR power supply enable). Disconnect the power and measure the diode value, no short. So we’ll need to track where is the DDRREG_EN comes from. As we can see from the schematic, it is transferred from PM_SLP_S4_L via R8111. 

And the R8111 is very close to the DDR power supply chip U7400.

Run the voltage value measurement on both sides of R8111, there’s no voltage.

Search the signal PM_SLP_S4_L on the schematic again. And check the other test points of  PM_SLP_S4_L on the motherboard.  

We can measure the high-level voltage on the R8179, but when measuring the diode value between R8179 and R8111, it’s shorted. 

Check the area between the two resistors we can see some corrosive phenomenon, scratch a little bit with the sculpture knife, find it’s the inner rail broken is caused by corrosion.

For the inner rail broken issue, we should jump a wire as the below figure to fix.

Jump wire on the real motherboard as below

After jumping the wire the short is gone, and assemble the MacBook to test, display function back to normal.

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