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820-4924 Only Powers from Battery

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Ryanlen2

Member
Hi -
I have a 820-4924 that had light liquid damage near SMC and U7001 but not really much. The board was missing PPBUS, but has been restored. This board will only power on if a battery is connected. Here are the measurements from AC adapter. Green/Amber light present. 85 Watt Original. Thanks.

PPBUS - 12.58V
PP3v42 - 3.428V
PPVRTC - 3.336V
PPVIN_S5_HS_Computing - 12.58V
PP18vDCIN - 16.6V
PP5V_S5 - 5.02V
PP5V_S3 - 0V
PP3v3_s5 - 3.35V
pp3v3_3 - 0V

Have a good one.
 
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Ryanlen2

Member
Hey Duke. Reflowed then replaced SMC. It still powers on with battery or battery and charger. Will not power on with charger only. Yes it charges the battery. If I want to power on with only charger I have to use a chinese charger. Weird. Other then that it works totally normal. Have green/Amber on both chargers. Thank you sir.
 
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dukefawks

Administrator
That would be a Q7180 or Q7010 problem. Not saying the actual FETs are bad it could also be resistors/traces to them.
 
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Ryanlen2

Member
Just wondering... What allows it to work with a Chinese charger and not allow original charger? Chinese charger works.
 
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Ryanlen2

Member
Thanks for that...
I have looked into the areas you suggested with no luck so far. I have checked traces, checked resistors in the area and replaced both Q7180 and Q7010. With original charger I am getting pulses of 16.60 - 16.80V on the DC-in connector. With the Chinese one I get a steady 16.5V in the same test location. Powers on automatically when magsafe is plugged in with a battery attached. What can I be missing?

Have a good one.
 
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dukefawks

Administrator
Measure voltages to both gates of Q7180 with the Chinese charger. Checked resistance between pins 17/18, 27/28 of U7100?
 
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Ryanlen2

Member
Hi Duke.

6.11v - 6.25v on S_Gate
6.21v - 6.29v on A_Gate


R7122 and R7121 were off. I replaced them as well as C7120 -23. It did turn on once with original charger after replacing the resistors, but hasnt since. Reistance on 17/18 - 3.8Ohm, 27/28 - 20.3Ohms. I replaced U7100 and Q7180 again, just to be safe.

Thanks man.
 
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dukefawks

Administrator
It could be something on PPBUS that is loading down the charger too much. Can you monitor current on a PSU and compare to a good board?
 
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