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820-34374-B PPBUS_G3H Shorted to ground

A

air_chair256

New member
hi i have got a macbook air 820-3437-B with liquid damage when you connect it to the charger green/orange light turns on but fan doesn't spin there was some corrosion around U6100 and SMC so i cleaned it up, on L7140 i got 1.8V that meant so i removed L7140 and pin number 2 is shorted to ground when i send 4V to pin number 2 the only thing that heats up is the CPU, on the schematic PPBUS_G3H doesn't go to CPU (PCH) also i checked for more shorted lines and i found all of the bellow rails are shorted to ground

PPBUS_G3H
PPBUS_G3H_R
PPBUS_S5_HS_COMPUTING_ISNS
PPBUS_S5_HS_OTHER_ISNS
PP1V05_S0_PCH_VCCACLKPLL_R

with diode mode it shows 0010 on both sides

i tried to remove some caps around the CPU but the short is still there, the problem can't find the short by detecting the heat because the only part that gets hot is the PCH

thanks
 
S

SMMRepair

Member
Probably s5_computing_isns that's shorting ppbus. Check all the tantalum caps on the front side of board...sometimes it's one of them that pops.
 
A

air_chair256

New member
Thanks for replying back, i removed all the tantalum caps and the short is still there there are some iC's on s5_computing_isns they can cause the short but i'm afraid of the PCH itself is shorted from inside, i looked for corrosion around CPU and it looks clean
 
J

JohnB8812

New member
Remove the fuse and check resistance to ground on pins 1 and 2 of where the fuse sits. You should get a short on one side of it. If it's on pin 2, inject low voltage first as the CPU sits on the system side.
 
A

air_chair256

New member
JohnB8812 said:
Remove the fuse and check resistance to ground on pins 1 and 2 of where the fuse sits. You should get a short on one side of it. If it's on pin 2, inject low voltage first as the CPU sits on the system side.
Click to expand...

yes i already did that and pin two is shorted to ground and when i inject voltage in only the CPU gets hot
 
A

air_chair256

New member
i injected 3.7V to PP1V05_S0_PCH_VCCACLKPLL_R and U8080 got hot but U8080 is not connected to PP1V05_S0_PCH_VCCACLKPLL_R directly so i checked the cap beside it (C8081) that has P5VS0_FET_RAMP on it and it was shorted to ground i removed U8080 the short on P5VS0_FET_RAMP and PP1V05_S0_PCH_VCCACLKPLL_R is gone but the short on
PPBUS_G3H
PPBUS_G3H_R
PPBUS_S5_HS_COMPUTING_ISNS
PPBUS_S5_HS_OTHER_ISNS

is still there
 
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