MacBook A1707 Kann nicht starten Problem Reparatur (820-00281-A)

Received a MacBook A1707 with cannot boot issue, board number is 820-00281-A.

● Check the Cosmetic

The customer said the MacBook cannot be booted, connect with an adapter, and power on to test, totally no response. Then disassemble the MacBook and take out the motherboard to check, there is no water damage trace and the cosmetic is also good.

Take out the motherboard and check, the cosmetic also looks good.

● Motherboard Chip-level Repair

• Schritt 1.  We should know the very basic boot sequence of MacBook is: generates the PP3V3_G3H >>> EC standby voltage generation  >>> the public voltage

As we can see from the above schematic, the PP3V3_G3H_REG EC is generated by the PWM circuit which is consisted of a U6903 (MAX77596 DRMOS) chip and an inductor L6900.

• Pin 2 is the power input
• Pin 8 is the enabled signal

Check the status of the inductor L6900 by the oscilloscope, the waveform is OK.

Check the voltage on the inductor L6900 is also good.

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• Schritt 2.  Check the 6 basic working conditions for the EC chip

        01. EC Standby VBAT and VDDA, the measured voltage on the inductor L5001 is 3.3V, OK!

        02. The second standby voltage for EC, PP3V0_S5_AVREF_SMC. It’s provided by the Pin 8 of U5165 (TS3330), the measured voltage value on C5020 is 3V, also OK. 

        03. EC XOSC0 standby clock signal, it’s outputted by the PCH U1100 SUSCL pin. The signal name is PM_CLK32K_SUSCLK_R, after getting through R5112 then change the name to SMC_CLK32K. Check the waveform on the R5112 is a standard sine waveform, which is also OK.

        04. First we should know how the EC RST signal is generated, it’s outputted by the pin H4 of U7000 (ISL9339) → R7090 →  SMC_RESET_L → R8592 → BUF_SMC_RESET_L → U5000. 

        05. Measuring and inspection process: we can measure the voltage on C5270. Pin #1 of C5270 is 0 volt, which is abnormal.

Then move forward to U7000, measure the voltage again on pin #1 of R7090 is also 0 volt.

Disconnect the DC power cable and measure the diode value on R7090 is only about 30, which is abnormal.

Remove the R7090 and measure the diode values again, pin 2 is normal, but the diode value on pin 1 which is close to U7000 is still very small. 

• Schritt 3.  Replace the U7000 with a new one, then assemble the Macbook and measure the EC reset voltage back to 3.3V, which is normal. The MacBook can be booted normally, and all the functions work well.

Zusammenfassung

The MacBook Pro A1707 cannot boot issue is caused by the EC RESET signal not OK, and the issue finally gets fixed by U7000 replacement.