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A1502 820-3476-A no light on charger, U7900 power cycling

Beto_MFC

Beto_MFC

New member
Working on this board that according to client died after he dropped the computer. Already swapped U7090 but no dice. Board has no signs of water damage.

Edit 1:

Managed to get pp3v42 stabilized to 0.9v after replacing a cap right before u7100. Then replaced u7100 and the voltage raised to 1.2v.

Edit 2:

I decided injecting 3.42v after the g3hot supply inductor, but the current draw is too low to be a short to ground (0.09a). Maybe the U7090 i put in was bad too.
 
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A

aprendiz

Moderator
Do you have green/orange light??? PP3V42_G3H present?? PPBUS G3H present and what voltage is there?? Also if it was dropped there is a big chance it have broken traces and could be a no fix.... Anyway lets measure first and see what wwe found...
 
Beto_MFC

Beto_MFC

New member
No light on charger but PP3V42_G3H is preset and now i'm only getting 1.2v. My guess now is that the buck converter LT3470AED is bad, as it was removed from a donor board.
 
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Beto_MFC

Beto_MFC

New member
PM_SLP_S4_L missing, haswell processor. Going to check all the input signals to see if some is missing. But as was a drop that caused the failure, i'm already considering a crack solder ball under the processor.
 
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Beto_MFC

Beto_MFC

New member
Got myself into a loophole now. Can't get the P5VS4RS3_EN to get the PP3V3_S4, all the logic aids powered by this won't be funcional.
 
Beto_MFC

Beto_MFC

New member
I have no PP3V3_S5 becouse U7501 doesn't get S5_PWR_EN. So I got stuck on this loop. Should I inject voltage at some point to see if I can pass on all S5 state rails?
 
Beto_MFC

Beto_MFC

New member
I really doubt, this board doesn't show the least sign of corrosion. It failed after a drop, my bet is that there's a crack on one of the processor balls. Anyway, will try reflowing the smc and get back with the resuls. PS: I don't have one of these 980YFE smcs here, just the other type.
 
D

dukefawks

Administrator
PPBUS should be 12.6V and there should be a green light. Without a green light the machine will never turn on. SMC is specific to each type of board, if you replace the SMC you need to take one from an identical donor board.

Also check voltage on SMC_ONOFF and ADAPTER_SENSE
 
Beto_MFC

Beto_MFC

New member
dukefawks said:
PPBUS should be 12.6V and there should be a green light. Without a green light the machine will never turn on. SMC is specific to each type of board, if you replace the SMC you need to take one from an identical donor board.

Also check voltage on SMC_ONOFF and ADAPTER_SENSE
Click to expand...

I can't use another same chip SMC really? Didn't know that it must be from same model board. I thought if it was the same chip it can be used, even saw Louis saying on a video that he used to buy chips with balls from ebay... Are you sure about that? I know SPI rom chips may have some problems with ME region, but SMC I really don't think so.

So to the measurements: SMC_ONOFF_L is 64mv and ADAPTER_SENSE is 3,35v. And also PPBUS is 12,33v. Remember Louis saying on a video that a bad SMC causes a drop on PPBUS voltage. Are we getting close here. As the failure was caused by a drop, will try reflowing the smc and get back with the results.
 
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