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820-2530, No green light-dead

Description

Board with liquid damage in the usual area.
No green light and no power.
We do have pp3v42_g3h.
U6901 had pin 5 gone. Replaced it and Jumped it to pin1 of VR5020…still no green light.
U6900 had the right voltages on its pins. Also we saw fluctuations on its pin 4, which indicates that it was communicating with smc.
Started analyzing the SMC…It had its supplies (AVCC, VCC and AVREF).
Noticed that SMC didn’t have its SMC Reset L signal, which comes from U5000.
First made sure that Q5032 was not shorting the signal to ground.
The chip had its Vin voltage. Had 0v on pin5 (CD), which should be around 3v.
C5001 didn’t seem shorted.
Replaced U5000 and got the green light and machine turns on.
Can’t hear a chime.
Machine has no backlight.
After probing around D9701 suddenly the machine started to have backlight, but something was burning hot. Then noticed that the fuse F9800 literally caught fire. Took it from A 820-2879 board. Replaced it and now have backlight.
Machine working fine but not chiming.
Found that we don’t have PP4V5_AUDIO_ANALOG. Traced it back to L6200. We replaced it and now U6201 is getting really hot.
Found short on PP5v_S3. It was caused by a shorted U4690. Replaced U6201 and U4690. Got all working including audio circuit and now have chime.
Noticed the machine wont charge or turn on from the battery.
Took measurements of Q7050 and it is working as supposed to. Also discarded problems with the IC that controls this since it is sending the right voltage to the gate.
From the battery connector I’ve found a short on pin 6 (smbus_batt_sda). Resistance was about 32 ohms.
Replaced D6950 and no more short to ground but board still wouldn’t work from battery or charge it.
Board wont turn on or charge the battery. If unplugged It would turn off slowly but lose display instantly. Mac OS shows an x and says there is no battery available.
I then decided to replace the SMC and now the board is charging and working from the battery normally. All ready to go.

Summary
Created by

ALRC

Completed on

March 2, 2015

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