820-00840 Liquid Damage with No Image/No Backlight (Turns on)

[ihelputech]

Hello all! I have yet another MacBook that is sad. ? It is an A1708 that does not have a backlight (and possibly no image) going to the display. The laptop was brought to me because water was split on the laptop.

• The first thing I checked was to see if the MacBook would take 20V and it does reach 20V through both chargers. It typically takes about 500mA at first then settles between 150-300mA.
• After opening, immediately noticeable was some corrosion near a few PPBUS _G3H caps, the area near U3890, and a couple other places. However, I did not find any shorts near those areas.
• I checked for warm spots on the board and I noticed the area near the display connector was getting hot. I thought this was just the CPU at first, but the heat seemed too focused. I then removed the display flex cable and saw more corrosion near J8500. The worst of it was near the 5V camera line (PP5V_S0_ALSCAM). L4010 was burnt and the line was reading somewhere between 0.3V-0.5V. I replaced. the burnt filter and C4013 for good measure. This resolved the short on that line and 5V was returned to that line.
• I checked the resistance on PPVOUT_S0_LCDBKLT and I recall it being lower than expected (somewhere around 500-2K ohms). I removed J8500 along with a couple of capacitors near the connected. The connector looked corroded/carbonized near PP5V_S0_ALSCAM &PPVOUT_S0_LCDBKLT so it needed replaced anyway. Once this was done and the pins were cleaned up with fresh solder, the resistance on PPVOUT_S0_LCDBKLT was restored to about 0.5MΩ.

The computer does turn on and boot to an external USB drive. I saw the activity light and I was able to remote into my copy of macOS while booted to this laptop. I also checked the continuity between the end of the display flex cable and some of the lines on the logic board to check the connections. All of the ones I tested seemed to work just fine. There is no corrosion near the area of U8400. I guess I'm just a little stuck on what to check next as everything else seems to be working. ?‍

Voltage Table:

PPBUS_G3H	13.05V
PP5V_S0	5.10V
PPVOUT_S0_LCDBKLT	0.01V
PPVIN_S0SW_LCDBKLT	0.08V
BKLT_EN_R	0.0V
PPVIN_S0SW_LCDBKLT_F @ F8400	13.04V
PPVIN_S0SW_LCDBKLT_R @ Q8400	13.05V
LCDBKLT_EN_L @ Q8400	12.93V
PPVIN_S0SW_LCDBKLT @ Q8400	0.10V (Resistance: 0.45 MΩ)
PP5V_S0_BKLT	5.10V

Thanks in advance for reading this! ?

 

[2informaticos]

First of all, welcome to the forum!

Compare diode mode (to ground) readings on eDP data lines; both left/right sides of C8520-29.
Usually spikes from backlight affect EDP_INT_AUX_N line.
This board has caps for separaton.
But these are 16V caps and backlight voltage is much higher.
You probably have now CPU with dead internal video (eDP) output.
Check if still gets external video.

 

[ihelputech]

Thanks for getting back to me so quickly!

Cap:	Pin 1	Pin 2
C8520	.259	ol
-21	.260	ol
-22	.261	ol
-23	.261	ol
-24	.261	ol
-25	.262	ol
-26	.257	ol
-27	.257	ol
-28	.254	ol
-29	.251	ol

Will any type-c video adapter work or would you recommend using an Apple adapter?

 

[ihelputech]

Update: I just tried a walmart-brand usb-c to hdmi adapter and I did not get any output. ? I'm going to try and find my Apple adapter to see if that makes any difference.
If the problem is an unorthodox overclock, is it worth trying to replace the CPU?

 

[2informaticos]

00840/875 are garbage boards, not recommended to waste such time.
The Intel Graphics should be fried now...

 

[ihelputech]

F

Thanks for your time helping me look into this!