820 00840 A Not booting up randomly, no known water damage. Just stopped working after screen repair

[lonelyworks]

I got an a1708 that is not booting up after an screen repair. I'm a bit of beginner into this, but I want to learn. I started checking voltage with some of the known point and got these:

PPBUS_G3H 0.4mv
PPDCIN_G3H_SNS 19.88v
PP5V_S5 0v
PP3V3_G3H 3.40v
PP3V3_S5 0.1mv

SMC_ADAPTER_EN - 0V
SMC_RESET_L - 3.4V
SMC_BC_ACOK - 1.06V
PP3V3_s5 - 0V

It seems like ppbus_G3H is shorted. Not sure though. What does that mean and what should I do next ? Since I'm learning, it would be nice to have an explanation of what's going on if possible

Thanks !

 

[2informaticos]

First of all, welcome to the forum!

Check diode mode to ground at PPBUS_G3H.
Read "HOW TO collection" thread, if needed.
If short, or low value, compare with the reading on big coils.

 

[lonelyworks]

Thanks

I checked with the diode mode to ground on PPBUS_G3H, got beep on all of the connection. All of them had a low value. I checked the big coils to ground and one of them didn't beep (L8410). I read the ''How to collection'' it helped understand. Let me know if I didn't understood something.

 

[2informaticos]

Forget not beeping coil.
You need to find a coil with the same readiing to ground as PPBUS_G3H (if exist).

 

[lonelyworks]

Okay. Got 0.2 ohm on PPBUS_G3H and got that same number on both R22 coil (L7210 and L7220).

 

[2informaticos]

Very likely dead CPU.

Remove U7210/20 (one by one) and check if PPBUS_G3H short disappear.
If yes, let the board to cool down and measure again ohm resistance to ground at L7210/20.