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

T

tentious

New member
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
 
2informaticos

2informaticos

Administrator
Staff member
"PPVRTC_G3_OUT - C1910 = 0v"
PCH will not work whitout RTC voltage.
This is also the reason U1900 gets hot; I bet short, or very low resistance to ground there.

First remove C1910, next check C1531-33.
If still the same, change U1900.
If not good yet, bad PCH.
 
J

JohnB8812

New member
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.
 
T

tentious

New member
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.
 
J

JohnB8812

New member
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.
 
2informaticos

2informaticos

Administrator
Staff member
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...
 
T

tentious

New member
Yeah, PCH is toast. I just toasted it to see if it would reflow or burn up crap underneath... but no go. Best reading is .02 ohms :-/.
So besides eBay, which I'd rather avoid, where's a good place to locate a replacement logic board? I already tried eBay but got a board that had the random shutdown problem that a lot of the 820-3787 board have. Would you recommend sticking with the 820-3787 or something else that has a better track record?
 
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