Apple MacBook Pro A2338 water notebook unable to boot repair

Machine model: apple MacBook Pro A2338

Main board version number: 820-02020-A

Fault:water damage Notebook Won’t Turn On

Maintenance process:

I received an Apple MacBook Pro A2338 laptop, and the failure description notebook water damage caused Won’t Turn On.
After disassembling the machine, the appearance inspection of the motherboard found that water damage and corrode in the backlight boosting part were serious.

Apple MacBook Pro A2338 water notebook unable to boot repair Figure 1.

There is corrode in the WiFi IC part of the back motherboard.

Apple MacBook Pro A2338 water notebook unable to boot repair Figure 2.

Clean the motherboard.

Apple MacBook Pro A2338 water notebook unable to boot repair Figure 3.

Apple MacBook Pro A2338 water notebook unable to boot repair Figure 4.

Measure the key points of the motherboard. First of all, where water damage is tested, the common point part PPBUS_AON,D impedance to ground is 300 ohms, the backlight boosting part circuit of corrode is serious, PPVOUT_LCDBKLT,1009 ohms is normal, other boosting IC UP800 parts are measured to be generally normal, and the back WiFi part, the main VCC part PP3V3_S2_WLBT_ISNS is tested to ground.

Test the Inductor seen by the motherboard again, and usediode; the one who lacks dialectical thinkingNo problem was found in the file test. Look carefully, the TYPE-C interface, two ACE 3217 sections, no abnormality, and the upper and lower sections, CC1CC2, PP3v3 _ UPC1 _ LDO PP1V5 _ UPC1 _ LDO _ core, no abnormality.
Power-on, the current meter is boosted from 5V to 20V, and the current is from 0.0250-0.0450-0.460-0.360.current of change, according to empirical analysis, is already the starting current.

Simple installation test, the screen lights up and enters the boot interface, but in less than 5 minutes, the computer automatically shuts down, checks DC power supply, displays 5, does not step up, and the current is 0.0240-0.0890.current of change back and forth. It is judged that VCC has Short circuit Current protection, which leads to the current back and forth current of change.
To solve the problem of 5V without boosting, the current goes back and forth from 0.0240-0.0890 current of change, starting with the following parts:

1. Test two TYPE-C interfaces, positive and negative measurements, and if the current is the same, temporarily determine that there is no problem with these two type-c circuits; If the current is different, the circuit Short circuit of that part is different.

2. Test the common point, and see if the impedance to ground is normal.

3. The fault was caused by water damage, which was measured from the components in the serious part of water damage, the backlight boosting part and the part near WiFi.
After measurement, problems were found in the back near WiFi.Short circuit appeared in the main VCC part of WiFi, and the impedance to ground was 0 ohm. Open Boardview to check the related components.

Apple MacBook Pro A2338 water notebook unable to boot repair Figure 5.
Use The rosin smoke method method, add 1V VCC Current heating test, and find the faulty components CL002 and CL053.

Apple MacBook Pro A2338 water notebook unable to boot repair Figure 6.

Remove the replaced components.

Apple MacBook Pro A2338 water notebook unable to boot repair Figure 7.
Power-on measurement, current boost is normal,booting up succeeded. Installation test, all functions are normal. This is the end of maintenance.