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820-2879-B Green Light No Boot

M

Mac-N-Sauce

New member
So I have another 2879 board with green light and no boot.
Have SMC_PM_G2_EN
PPBUS_G3H is .65v
Liquid damage on back side of board near Q7560, some corrosion on c7561,c7563
Looking for some direction
 
M

Mac-N-Sauce

New member
PPBUS_G3H 1.06k measured at F7040, diode mode at .445v, resistors check out at 10 and have continuity to the ISL, no corrosion around ISL. I do get the 12v rail only when battery plugged in but I do not get orange light or boot
 
M

Mac-N-Sauce

New member
I did get 12.6v on pin 1 of the fuse once removed, but no PPBUS, i also have 15.06v on charger a gate
Ok, I seem to be getting the 12.56v, but its fluctuating. It starts at 12 and then drops, then spikes back to 12.
 
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M

Mac-N-Sauce

New member
Quick update: Because of the fluctuating voltage and how low it was, I decided to replace the boost capacitor C7025. I now have steady voltage on PPBUS, but it is low at 9.56v
If i understand what you are asking I put the probes on the top of the caps individually? If so I got OL on both, if not, them explain exactly where to put the probes!
Be nice :)

It seems something is pulling the voltage low.
 
A

aprendiz

Moderator
Red probe on pin 1, black probe on pin 2 from C7050 and the same procedure on C7020........ Measure resistance....
 
M

Mac-N-Sauce

New member
C7050 = 3 OHM
C7020 = OL
I aslo have another issue: I have now lost my green light for some reason, i would assume my ISL?
 
M

Mac-N-Sauce

New member
OK, I replaced the ISL and I have my green light back, but I am back to a fluctuating 12.6v PPBUS_G3H
Any help would be appreciated
C7050 = 3 OHM
C7020 = OL
 
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M

Mac-N-Sauce

New member
Ok, finally got back to this one. I replaced r7021, c7020, r7022. resistors measure correctly. I have continuity between all components so traces are fine. I get 12.6v but it constantly fluctuates. I went back to the Q7085 and I get 16.5v for a couple of seconds, then it fluctuates down to about 3.4 and jumps back up to 16.5v and repeats.
I get the same result at R7020
At R7021 it drops to 15.8v on pin 2, at R7022 it is at 16.5v all voltages fluctuate. The corresponding pins on C7020 are the same 15.8v and 16.5v, So unless i am mistaken this is working correctly. Of course i am not really sure if it is supposed to fluctuate and the computer still has green and no orange with battery and will not boot.
Charger A Gate is 17v

Any ideas
 
D

dukefawks

Administrator
Remove F7040 and see if it is stable. If not then probably dead ISL or badly soldered. Check all traces in the sense circuits from pins 17,18 and 27,28 to the sense resistors.
 
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