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820-00840 20V, 0.04A after liquid damage

2informaticos

2informaticos

Administrator
Staff member
Latest values are too high comparing with good board.
You may have bad solders, due to corrosion.
I hope all readings are with red probe at ground.
Compare the values on all big coils; use ohm scale for very low values.

Check output voltages of U7800 (7 OF 10), page 60.
 
it-solve

it-solve

Member
Yes, red probe to ground. Values of other coils are very close if not identical to the good board.

Will touch up the corroded lines. No falling off components while poking around.

Outputs of 7/10 U7800
PP3V3_PDO3V - 3.21V
PP1V25_VREF - 1.21V
PP5V_LDO5V - 4.91V
 
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it-solve

it-solve

Member
Now after replacing C3706, C3708, C3700
Fixing corrosion on pads of R3771/2, R2892/3
Lifting and resoldering U8400 and R8450/1

I get 5V 0.02A. Not detecting any short on the bigger coils, nor on the pads of the components, I replaced/resoldered
 
it-solve

it-solve

Member
SMC_ADAPTER_EN - 0V
SMC_PM_G2_EN - 0V
PP3V1_RTC - 0V
PMIC_EN_P3V3S5 - 0.17V

Also seems like I have lost PPBUS_G3H
PPBUS_G3H - 0.012V
PPDCIN_G3H - 5.1V
PP5V_S5 - 0V
PP3V3_G3H - 3.41V
 
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it-solve

it-solve

Member
Ok got the PPBUS_G3H back. Who knew missing TBT_X_ROM_HOLD_L would cause CD3215 not to get to 20V

Im back to 20V 0.04A with:

SMC_ADAPTER_EN - 0V
SMC_PM_G2_EN - 3.41V
PP3V1_RTC - 0.462V
PMIC_EN_P3V3S5 - 0V

There is no liquid signs around U7800
 
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it-solve

it-solve

Member
PP3V1_RTC - 0.047 on this board - 0.462 on a good board. NO visible corrosion or liquid near U7800.

My only donor board reads 0.0021 on PP3V1_RTC, that's probably not good for U7800 swap if needed? On the other side, PP3V_G3H_PCH_VCCRTC goes into the CPU. Lost cause?
 
2informaticos

2informaticos

Administrator
Staff member
Yeah, CPU, or U7800 problem.
Just in case, remove C1227/28 and C7922.
If still low value, you can try to heat U7800 and/or CPU; hoping is accumulated crap issue.
At the end, removing U7800 is also an idea...
 
it-solve

it-solve

Member
With lifted up C1227/28 and C7922 I get 20V 0.46A and the board is turning on. I Resoldered back then and still seems to turn on.
Back in the case fan spins but no picture or response from the keyboard. Tried SMC reset, doesn't completely do it. 0.45A -> 0.02 -> 0.45A . Usually, I can see all zeroes on current and restarting the charger when I do SMC reset.

Reflowed U7800, still no picture. Not sure if it got reflowed ok, hard to make it dance.
I Can see the CPU gets hot.
 
2informaticos

2informaticos

Administrator
Staff member
Looks like stuck in 0.95V.
It should drop to 0.6V, when the board boots.

Possibly PCH/CPU issue.
Try known good BIOS, just in case.
 
it-solve

it-solve

Member
20V 0.03A - 0.11A with spare bios chip from the same model board. Soldered U6100 back and getting 20V 0.03A - 0.11A as well. Maybe you are right, corroded or cold joint somewhere
 
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