Motherboard No.: 820-00165-A
Malfunction:
Macbook Air A1466 2016 Version Can Not Boot Up, the current changed from 0.03A to 0.126A, and stayed at 0.126A.
Troubleshooting:
There are two main reasons can cause this kind of issue.
1. Some of the power wasn’t generated;
2. SMC, BIOS data or other parts was broken;
We removed the back cover and disconnected the battery, connected with DC power machine and power on, the current jumped from 0.03A to 0.126A, and stayed at 0.126A. We disconnected all parts, connected with power and turned on again, the current was the same, it means the problem was from the motherboard.
We disconnected the power, took out the motherboard, and checked the motherboard, there wasn’t any water damaged area or other obvious damaged area. We connected power and check the voltage on the inductors.
PP5V_S4RS3 on L7520 was 5V, normal;
PP1V2_S3 on L7430 was 1.2V, normal;
PP1V05_S0 on L7630 was 1.05V, normal;
PPVCC_S0_CPU on L7320 was 0V, abnormal, normal value should be around 1.8V;
According to the measuring result, the voltage wasn’t generated on L7320, and current stayed at 0.126A.
We opened the schematic and found out the circuit which generated the voltage connected with L7320.
According to the schematic, we could see the voltage PPVCC_S0_CPU on L7320 was generated from the mosfets Q7320 and Q7321 which were controlled by U7320. U7320 was controlled by CPU power IC U7200 as the following schematic showed.
We continued to check the working conditions of U7200,
PPVIN_S0_CPUVR_VIN was 8.6V, normal;
PP5V_ S0_CPUVR_VDD was 5V, normal;
CPU_VR_EN was 0V, abnormal, normal value should be around 1.05V;
The signal CPU_VR_EN was from U0500 CPU. According to the working timing sequence, only when CPU got the signal CPU_VCCST_PWRGD, the signal CPU_VR_EN could be sent out to enable the power supply of core CPU.
We continued to look for the source of CPU_VCCST_PWRGD, it was generated from U1930.
We connected with power to check the voltage on CPU_VCCST_PWRGD, the value was 0V, and then we checked the voltage on pin1 of the resistor R1931, the value was normal, 1.05V. We disconnected the power and checked the resistance on R1931, the value was 10K Ohm, which was also normal, it means the signal CPU_VCCST_PWRGD wasn’t generated from U1930.
We connected with power to check the working conditions of U1930:
The voltage on VCC_PP3V3_S5 was 3.3V, it was normal;
Voltage on PM_SLP_S3_L was 3.3V, which was also normal;
Voltage on ALL_SYS_PWRGD was 0.731V, which was abnormal, normal value should be around 3.3V;
According to the measuring result, we concluded that the signal on ALL_SYS_PWRGD was abnormal, so that U1930 couldn’t output CPU_VCCST_PWRGD, then we continued to look for the source of signal ALL_SYS_PWRGD.
ALL_SYS_PWRGD was generated from P1V8S3_PGOOD，P5VS4RS3_PGOOD，P1V05S0_PGOOD，DDRREG_PGOOD and resistor R8162 and pull-up power supply PM_SLP_S3_BUF_L. If anyone of the PG was abnormal, the signal ALL_SYS_PWRGD will be abnormal.
The signal ALL_SYS_PWRGD was also protected by Q8150, and what’s more, PP5V_S0，PP3V3_S0，PP1V5_S0 should be normal, then the signal ALL_SYS_PWRGD will be normal.
We connected with power and checked the voltage on pin 1 of R8167, the value was 3.3V, which was normal, the voltage on pin 2 was 0.731V, which was abnormal. We disconnected the power and checked the resistance, the value was 10K Ohm, which was normal, it means the problem was from the circuit afterward to make the signal abnormal.
We removed the mosfet Q8150 to exclude the possibility of abnormal PP5V_S0，PP3V3_S0，PP1V5_S0 which can make the signal ALL_SYS_PWRGD abnormal. Then we checked the voltage on ALL_SYS_PWRGD after we removed the mosfet Q8150, the value was 3.3V, which was normal.
It means the problem was from Q8150 which made the signal ALL_SYS_PWRGD abnormal. We replaced the mosfet Q8150 and checked the voltage on ALL_SYS_PWRGD again. The value was still 0.731V. It means the problem was from one of the three power PP5V_S0，PP3V3_S0，PP1V5_S0.
VMON_5V_DIV was generated from PP5V_S0 via R8151 and R8152, the value was 1.07V, we check the voltage on pin 2 of R8153, the value was normal, 1.07V. VMON_3V3_DIV was generated from PP3V3_S0 via R8158 and R8159, the value was 1.07V, we checked the voltage on pin 2 of R8154, the value was just 0.3V, which was abnormal, then we checked the pin 1 of R8154, the voltage was 1.07V. We disconnected the power and checked the resistance on R8154, the value was 1M Ohm, which was abnormal.
Summary
The resistor R8154 was broken, and the resistance was much bigger than normal, it makes the voltage on ALL_SYS_PWRGD lower to 0.731V, and the PPVCC_S0_CPU was 0V, we replaced the resistor, the problem was resolved.
