Macbook Pro 2012 15" possible short on 3v3_S0

[Askic]

Hello guys,

I have faulty 15" Macbook Pro 2012 with 820-3330-B motherboard with the following symptoms:
- when turned ON, there is a short increase in current to up to 0.8A (power supply unit display)and then back to zero.
- during this short time, one FAN try to spin (better to say vibrate).

I have done measurements on power rails and found that PP3v3_S0 is most likely shorted to ground. Multimeter readings are the following:
- 0.017 in diode mode (positive leas is on ground)
- 16 ohm t ground in resistance mode.

I'm pretty sure this is the culprit, but there are so many components connected to this power rail, and I don't have a thermal cam, so I wonder if it would be possible to find a faulty component by voltage injection

I have a lab PSU 0-30V, 0-5A. What would you recommend me to do? Where is the right spot to try to inject the voltage?

Thank you.

P.S: SMC is running (PPBus_G3H is 12.56 V), and there is PP3V42_G3H, since there is a green light on the charger.

[Askic]

Re: Macbook Pro 2012 15" possible short on 3v3_S0

I'd like to provide a bit more information.
All 5 big coils L(7510,7520,7530, 7550, 7560) have 1.3 ohm to ground or more precise 1 ohm to ground (resistance of multimeter leads is about 0.3 ohm).

Mosfet Q7810: 3.3V S3: PP3V3_S3_FET has 0.36 V to ground (in diode mode)
Mosfet Q7830: PP3V3_S0_FET pin 5 has 0.016V to ground, while PP3V3_S0_P3V3S0FET pin 3 has 0.138 V to ground or about 140 ohm to ground. This pin is actually PP3V3_S5.

[Askic]

Re: Macbook Pro 2012 15" possible short on 3v3_S0

Hello, just want to update and provide more information in order someone to be able to help or give some useful advice.

When injecting 3V into 3v3_S0 line, I noticed that U9220 (DP AUX, DDC, & HPD muxing to IG/EG) is getting hot.
After removing this chip from the board, resistance od 3v3_S0 line was restored to 1.9 kohm, which is to be expected (it was 16 ohm with U9220 on the board).

I think that U9220 is not a critical component to start the MBP, so I tried to start without U9220, but no luck.

I have noticed that PM_SLP_S4_L is missing, so this is the main problem now. As far as I can conclude from the schematics, PM_SLP_S4_L is an output signal from U1800 chip. Is there any more I can do now?

[piernov]

Re: Macbook Pro 2012 15" possible short on 3v3_S0

https://logi.wiki/index.php/User:Pie....2C_what_do.3F

[Askic]

Re: Macbook Pro 2012 15" possible short on 3v3_S0

Hello Piernov,

first of all, I don't have original 85 W charger for this laptop. I use PSU with Magsafe1 cable (L style connector). However, I also have a good working battery. I tested this with battery.

I do have PM_SUS_EN and SMC_BATLOW_L when battery is connected, so I think this issue is not due to non original charger.
I have also noticed that when battery is connected and I turn ON my PSU (connected to the board), there is a short pulse on PM_SLP_S4_L (about 1 sec 3.2V) and then zero.