Macbook A1466 2016 Version Can Not Be Turned On

Motherboard No.: 820-00165-A

Phänomen der Fehlfunktion:

There was charing current when connected with power cable, the it can not be turned on when press power button.

Possible Reason:

There was charging current when connected with power cable, it means the PPBUS_G3H was normal, if there it’s abnormal, there shouldn’t be charging current when connected with power cable. So the possible reasons are the following two points.

1. The working conditions of chips in standby circuit  was abnormal;

2. Working conditions of chips in standby circuit was ok, but the circuit works abnormally;  

Fehlersuche:

We removed the back cover, disconnected the battery, and connected with power cable to turn on the macbook, it can not be turned on, and the charging current was around 0.015A, which was abnormal, normal value should be around 0.025A.

We disassembled all parts, connected power cable with motherboard independently, the currnet was still the same, value was 0.015A, it means the problem was from the standby circuit.

We disconnected the power, and took out the motherboard to check if there any obvious water damaged or broken area. After we checked the motherboard, we found that there was a very serious water damaged area at the back side of motherboard.

We used PCB cleaner to clean the corrosion and checked if there was any component was corroded.

After cleanning, we found all of the components seems normal, we connected with power to check the current again, the value was still 0.015A, so we had to check the standby circuit step by step.

We checked the voltage of standby circuit

PP3V42_G3H  was 3.42V, normal;

PPBUS_G3H was 8.6V, normal;

PP3V3_S5_REG_R was 3.3V, normal;

The 3 sets of voltage above were normal means the 4 chips LT3470AED(U7090)，ISL6259(U7100),   SMC(U5000) , TPS51980A(U7501) were normal.

We continued to check the standby conditions of PCH.

We opened the timing sequence chart and checked the power supply for RTC of PCH, we opened the schematic and found out the RTC rail. (We can search by keyword VCCRTC in schematic to locate the RTC rail), then we connected with power to check the power PPVRTC_G3H by checking the voltage on pin 1 of C0890.

The value was 0V after we checked, which was abnormal, normal value should be around 3.3V. We continued to look for the the source of VCCRTC by search with keyword PPVRTC_G3H in schematic.

It’s from the clock chip U1900, we opend the bitmap and checked with motherboard, this was the area where was water damaged.

Then we continued to check the working conditions of U1900, the power for U1900 was PP3V42_G3H, it was inputted from pin 13 of U1900. We checked the voltage on pin 13, the value was 3.42V, which was normal, then we disconnected with power and checked the diode value on pin 1, the value was 426, which was also normal.

The working conditions or U1900 were normal after we checked, but there wasn’t any power outputed from it, so we concluded that U1900 was broken.

We replaced a new U1900 and checked the current, it was back to normal, and the macbook was turned on automatically, we assembled all parts and power cable to test again, all functions were normal, problem was resolved.

Zusammenfassung:

The motherboard was corroded, clock chip U1900 was broken, and the voltage VCCRTC can not be generated, and the standby condition of PCH was abnormal, then the macbook can not be truned on, we replaced another U1900, problem was resolved.

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