The model for this MacBook Pro is A1502, the motherboard model is 820-3476-A, which is released 2013, with 13-inch LCD screen.
Disassemble the rear case, disconnect the MacBook battery, and connect it to the DC power supply to test it, first we see the MacBook current is 0.02, after standby, and trigger it automatically, it stuck at 0.13. This current phenomenon is usually caused by a lack of voltage or low voltage, which causes the MacBook motherboard not to work.
Use digital multimeter to measure the voltage for each inductors, when measured inductor L7310, the value measured is 0V, which is abnormal.
Login ZXW Dongle to check MacBook schematic diagram to find F7310, we know that this inductor is CPU core power supply, CPU power supply IC U7200, control U7310 through the upper and lower M0S tube, through the inductor L310 and then produce PPVCC_SO_CPU. So, we're focused on checking the working conditions of the CPU power supply IC.
If the CPU want sent out the CPU_VR_EN, it needs receive the CPU_VCCST_PWRGD voltage first, and then can receive the B59 Pin.
Measuring it with digital multimeter, it only has 0.5V, while the normal value is 1.05V, obviously the output has some problem. 1 Pin 3.3V is normal, 2 Pin ALL_SYS_PWRGD is 0V, so we need to check ALL_SYS_PWRGD. Check the source of the ALL_SYS_PWRGD on the schematic diagram.
It's summed up by several PG, we can disconnect these capacitors and then measure the all _ sys _ PWRGD voltage to determine whether these PG pull low voltages or other reasons.
Open the bitmap, find R8169,R8165, R8164,R8168,R8162 respectively, disconnect these capacitors, and then measure it, it's found that each PG output are normal, it's 3.3.V, which means it's not pull low voltages by PG. Next check ALL_SYS_PWRGD.
According to the schematic diagram, we need to check protective tube Q8150. Find Q8150 on the motherboard, observe it under the Double Arm Microscope, it's moldy, possibly this damaged tube pulls down the voltage.
Assemble the MacBook Pro, press the power button, now the MacBook is turned on smoothly, the problem has been fixed.