MacBook A1502 Can not boot issue repair.
Model: A1502 (EMC 2875)
Board No.: 820-3476-A
Defect Phenomenon
The customer said the A1502 MacBook cannot boot, and the green light does not work. Can use the adapter to boot normally, but can not charge. Now, the Macbook cannot boot.
Connect with the DC power supply, there’s only a 0.009A current. Besides that, the green light indeed does not work and there’s no any current change when pressing the power button.
Then confirm with the client, that it’s OK to disassemble the MacBook and check the details inside.
After disassembling and checking the details of the motherboard, there are no obvious burn or water damage marks.
Next, let’s measure the voltage values on the important nodes.
First, measure the voltage PPBUS_G3H on the test point F7140
The measured voltage is 14V, which is normal.
Then continue to measure the PP3V42_G3H on the L7095, the measured voltage is 3.4V, which is also normal.
Then the next step, based on the repair experience. Let’s check the basic working stations of EC U5000.
As we measured the standby voltage of 3.4V is OK.
Then measure the reset signal, only 0.6V can be measured. Which is abnormal
So the problem is relative to the EC reset signal. How can we know where the SMC_RESET_L signal comes from? By tracking the schematic, we can see SMC_RESET_L is outputted from pin #5 of U5110. It will be generated when the PP3V42_G3H is provided to U5110, then pulled up by resistor R5110.
Then measure the diode value on the pin 5# of U5110 to have a check. The diode value is 467, within the normal range.
The voltage value on the RESET signal is too low, which might be caused by the chip U5110 or the small resistor R5110. Let’s start with the easier tasks before moving on to the more difficult ones, replace a new pull-up resistor R5110 first.
After that, the green light works fine and the MacBook can work normally.
A 3.3V voltage can be measured on the reset signal.
The issue gets perfectly resolved by R5100 replacement.
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