820-3787 - No Boot - No Fans - No S4 Rail

[tentious]

Battery will charge when connected and when complete, I get green light. I get orange light with board out and fans connected, but no fans. There is no liquid damage, this is my personal laptop. I know.... but I promise there "should" be no liquid damage.

S5 rail seems ok, but S4 is either shorted or not supplied.

Here's some data, I thought U8170 is interesting, possibly needing to be replaced?

PP3V3_S5 - PP3V3_S5_PWRCTL - C8170 = 3.33v
S4_PWR_EN - D8174 = 0v
PM_SLP_S5_L - R1222 = 0v
SMC_S4_WAKESRC_EN - R5190 = 0v


I thought that U1900 was interesting too. It's particularly warm to the touch and shows up on the FLIR camera.
PP3V3_S5_REG - L7560 = 3.33v
PP3V3_S5_SYSCLK - C1902 = 3.33v
PPVRTC_G3_OUT - C1910 = 0v

 

[JohnB8812]

Voltage on PPVRTC_G3H? If zero, check resistance to ground on PPVRTC_G3H. Sounds like probably a bad clock chip

 

[tentious]

PPVRTC_G3H - R1100 = 0v / 0 - ohms resistance to ground.

 

[JohnB8812]

Remove U1900 to see if short goes away. If so, resistance will go back to many kilohms and you simply had a bad U1900. If not, remove C1910 next.

 

[tentious]

Thanks for the help. It is possible to remove C1910 first to see if this is the short? I can remove U1900, but this is more difficult for me. If C1910 is the cause and is removed, I'm assuming I should see PPVRTC_G3H with higher resistance? If not and short still exists, I'm assuming U1900 is the problem?

I have a donor board coming for capacitors/resistors/etc, but it will be a week or so... china board with procs/memory chips removed. I've already ordered a U1900 from here, should be here next week.

 

[2informaticos]

"First remove C1910, next check C1531-33.
If still the same, change U1900."

 

[tentious]

"First remove C1910, next check C1531-33.
If still the same, change U1900."

Awesome! Thanks! Sorry, I missed your post earlier.

 

[JohnB8812]

Yeah you can always remove the caps first. Remove C1910 check. If nothing check caps like 2informaticos said. If still short remove U1900. If it's still shorted with all the caps and the chip off, then it's the CPU.

 

[tentious]

Yeah, so just removed C1910,C1531-C1533 and PPCRTC_G3H is still shorted. :-/ I'll remove U1900.

 

[JohnB8812]

All good! If it relieves the short then this is fixable! So keep confidence lol

 

[tentious]

Bad news, I removed U1900 and PPCRTC_G3H is still shorted to ground. Do I have a new donor board?

 

[2informaticos]

If you have 000, pretty sure bad PCH.
Low value, like 050-350, could be result of crap under PCH.
Put good flux and heat to 180-200 degrees; you have nothing to lose...

 

[JohnB8812]

Yeah unfortunately dead PCH. I've seen that a few times now weird failure on some of the newer boards.