820-00850 Liquid Damage to PPBUS_HS_CPU C7214 - 5v no Boot

[ClerkenwellMacs]

Have an 820-00850 A1989 13" Pro 4 Thunderbolt Port.

Liquid damage to C7214 only, was totally burned out with burning electrical smell. Shorting to ground for sure.

Getting 5.1v on USB

No liquid to anything else.

Fried CPU?

Cheers

 

[2informaticos]

Very likely.
What is the ohm resistance to ground on PPBUS_G3H?

 

[ClerkenwellMacs]

1.7 ohm ?

 

[2informaticos]

Remove U7210/20 (one by one) and see if short disappears..

 

[ClerkenwellMacs]

Tried removing one at a time and then both,

U7210 Only 1.7 ohm
U7220 Only 1.7 ohm
Both Off - 1.6 ohm

 

[2informaticos]

I was expecting ohm resistance to ground at PPBUS_G3H...
Where did you measure?

 

[ClerkenwellMacs]

I measured at PPBUS_HS_CPU the first time, have just measured PPBUS_G3H and its the same.

Does that sound right or am I making a mistake?

 

[2informaticos]

PPBUS is the same, just separated with miliohms resistor.

If you still have short, is time to check now U7410/20/30.

 

[ClerkenwellMacs]

I am getting 2.2 ohms on PPBUS_G3H with all U7410/20/30 off.

I removed them and re-applied individually with no change in ohms.

So currently I have U7210/20 and U7410/20/30 off the board and still have the short.

 

[2informaticos]

Check if any other coil has the same resistance to ground.