820-3115 (MBP mid 2012 13") works only after heating up SMC region

[Beeldbuisje]

This MacBook was slightly water damaged, had not a stable PPBUS_G3H due to a broken wire in the battery charging circuitry. (Pin 4 of R7050 to R7052 pin 2)

After repairing this, the Macbook worked stable for +/-5 days without battery (defective PCB IN the battery, so disconnected for now). This morning after plugging in, nothing again.
PPBUS_G3H only 2,9V. I forced SMC_RESET_L down. PPBUS_G3H became 12,2V.

I decided my problem would be around the SMC. I discovered when I heated the SMC slowly with an hairdryer, the computer boots up and keeps working.
After power down and the SMC region cools down, nothing but a green charger light and too low PPBUS.

Is this a know issue, or maybe dirt under the SMC chip?

thanks!
Gert

[zpi]

Re: 820-3115 (MBP mid 2012 13") works only after heating up SMC region

Usually Capacitors reacts to heating.

Check U5010 circuity (its nearby SMC) it has to work if you want SMC to start its job . Pin1 and Pin3 is getting Voltage? Also maybe C5020 is shorted? Try to measure ohms to ground on C5020 pin1 (with charger disconected)

[piernov]

Re: 820-3115 (MBP mid 2012 13") works only after heating up SMC region

The SMC itself shouldn't cause PPBUS_G3H to be 2.9V instead of 12.2V/12.6V. The SMC can cause PPBUS_G3H to be 12.2V instead of 12.6V.
In any case if PPBUS_G3H is stuck at 12.2V (no battery) I'd make sure SMC_RESET_L and PP3V3_S5_SMC_VDDA are always 3.42V, then reball SMC, and replace it if still not working.

[Beeldbuisje]

Re: 820-3115 (MBP mid 2012 13") works only after heating up SMC region

SMC_RESET_L and PP3V3_S5_SMC_VDDA are always present.

PPBUS_G3H is really 2,9V. If I short SMC_RESET_L to ground, G3H rises to 12.2V. (After heating up SMC G3H rises to 12.6V and the MacBook boots)


I think the circuitry around U5010 doesn’t make sense here, because when I manually resets SMC (R5000 short to ground for a while), I’ve the same behavior as when I plug in the charger.

[zpi]

Re: 820-3115 (MBP mid 2012 13") works only after heating up SMC region

If you really heat only smc, then just try to change it, probably fastest way to find out

[Beeldbuisje]

Re: 820-3115 (MBP mid 2012 13") works only after heating up SMC region

If you really heat only smc, then just try to change it, probably fastest way to find out

The PCB extracts a lot of heat. By heating up SMC, everything in 2cm2 becomes warmer.

I don't have my own reballing machine. So I want to be sure ;-)

[zpi]

Re: 820-3115 (MBP mid 2012 13") works only after heating up SMC region

You dont need reballing machine to reball smc, only stencil, balls and air station. When i want to make only one chip hot, i put thermal pad on that chip and put soldering iron on that thermal pad.