Macbook Air A2681 Board 820-02536 No Power - 5V 0.025A

[TimScrawn]

I have an m2 air A2681 here today that is just giving 5v @ 0.025amp draw. No liquid damage or prior history of repairs. No power at all. Checked the following lines:

PPDCIN_AON_CHGR = 5V
PPBUS_AON = 12.36v
PPBUS_5vS2_VIN = 12.3v
PPBUS_3v3_S2_VIN = 12.3v
PP3V8_ON = 3.8v
PP1V05_S2SW_VDD2H = 0v
PP1V25_S2 = 0v

I have replaced U5200, R5215 & R5216. Checked ohms on both resistors. Both tested good. Little bit stumped on this one. Any help would be greatly appreciated.

[TimScrawn]

I have a feeling this is a PD rom problem to be honest.

[mon2]

PP1V05_S2SW_VDD2H = 0v

What is the resistance to ground of this rail? Do not have power to the board when testing the resistance.

[TimScrawn]

Hi Mon, thank you for responding. I get 25 ohms to ground on PP1V05_S2SW_VDD2H

[mon2]

At 25R ohms, to me, this rail is not shorted.

5v @ 0.025amp

This is a very low current draw. The PD controller is at 5v so your downstream regulators are in a boost mode. Suggest to review the PD controllers and test each of the LDO rails. Also check for any shorted caps in this region.

[TimScrawn]

Hi Mon,

Thought I would just come back and give you an update. So one of the PD controllers I have since replaced from a donor board in the exact same position, no difference. I then took the SOC rom off and re-programmed, still no difference. I have checked all voltage rails within the PD controller area and there are no shorts or missing rails. The only one I can see that could be off is my p5v_s2 rail. Not sure where to progress from here?

Thanks

[mon2]

What is the resistance to ground (no power to the board) of PP5V_S2?

Do you have a voltage on the enable pin for this power rail @ P5VS2_PWR_EN?

The above are linked to UC300.

[TimScrawn]

What is the resistance to ground (no power to the board) of PP5V_S2?

Do you have a voltage on the enable pin for this power rail @ P5VS2_PWR_EN?

The above are linked to UC300.

I will check for you now, thanks bud

[TimScrawn]

Okay, I get 12.3v on the Enable pin of UC300

The resistance to ground on pp5v_s2 is 1 mega-ohm and lowering

[mon2]

12.3v on the Enable pin of UC300

Can you double check this measurement? This is way too high and should be 1v8 or lower. Otherwise, something is wrong here.

That is, the enable signal is driven by a logic gate that has 1v8 for the VCC pin so the max voltage here should be 1v8.

Perhaps you have measured one of the VIN pins on UC300?