Macbook A2442 no display board 820-02098

[dbuergi]

Hi all,

i got a Macbook A2442 which statrts normal but is not showing any picture. Using an external monitor works fine. After opening the Macbook i found a dried up line of liquid damage around CN979, RD503, and UP730. I cleaned up everything and also unsoldered the chips to clean the pads. There were no shorts before but i still don't have any picture. Sometimes you can see a glimpse of light in the middle of the display.
So before i change the whole display i want to make sure that it's not any issue with the logicboard. So any ideas what i can check next?

[mon2]

Would you have a thermal camera? Suggest to remove the heatsink off the CPU and inject 1v only onto fuse pad # 2. You should see a high current spike and the device that is shorted should glow like a Christmas light. Check top / bottom side of the board for hot spots. For now, do not go higher than 1v. The high current injection should be ample to make the shorted part suffer.

[dbuergi]

Update here, there was some dirt under UP800. Reballed the chip, checked with USB-C tester (everything fine and 20v), but it back in the case and started the Macbook. I got the chime and suddenly it went off.
I think my big mistake was to use it with my HP docking station via USB-C...
No i have a short on PPBUS_AON (5V and 0,00 to 0,01A). Injecting 1V with 5A only showed head at my injection spot. Any ideas what to do? Since there are many tantal caps i could go up with the voltage?

[mon2]

Remove all power. Meter in resistance mode. What is the exact resistance to ground of PPBUS_AON?

[dbuergi]

Hello mon2,

it's 0,4 Ohm.

[mon2]

Flux and remove fuses F5200 and F5201 off the board.

Then confirm which side of the removed fuses is shorted. Is it the producer (ISL; upstream) or consumer (downstream) side with the low resistance to ground?

[dbuergi]

Consumer side shows 0 Ohm.
Just to be sure with ISL you mean U5200 right?

[mon2]

Yes, ISL = U5200 = upstream point of view from the fuses.

To confirm, fuse F5200 / F5201, pin #2 = downstream and is the side with the short?

If you power up now, without the referenced fuses, what is the voltage to ground of PPBUS_AON as measured on fuse pad # 1 of F5200 or F201?

[dbuergi]

Yes it's the downstream.
Pad 1 on both fuses show 12,28V.

[mon2]

Would you have a thermal camera? Suggest to remove the heatsink off the CPU and inject 1v only onto fuse pad # 2. You should see a high current spike and the device that is shorted should glow like a Christmas light. Check top / bottom side of the board for hot spots. For now, do not go higher than 1v. The high current injection should be ample to make the shorted part suffer.

[dbuergi]

Made a voltage injection and LP800, QP800 and QP803 are heating up. So it should be something faulty in this area?
Any conclusion or do i have to take surrounding caps and mosfets out to find the shortet component? Maybe i should start with QP800 and QP803 to check if they have an internal short?
At least it speaks for my test with the HP dock to cause this fault to the backlight circuit.

[dbuergi]

Double post sorry

[dbuergi]

Would you have a thermal camera? Suggest to remove the heatsink off the CPU and inject 1v only onto fuse pad # 2. You should see a high current spike and the device that is shorted should glow like a Christmas light. Check top / bottom side of the board for hot spots. For now, do not go higher than 1v. The high current injection should be ample to make the shorted part suffer.

I guess i found the faulty chip. I unsoldered LP800 to isulate the short even more and after removing QP800 short is gone. I'm going to get a replacement from Digikey asap.
One more question since my UP800 shows a little crack at one corner. Is it safe to get a replacement from Aliexpress or is any extra proramming / special donor chip needed?