820-01958 with pulsing power rails

[sekidata]

MacBook Air 2020 820-01958 Intel. No corrosion visible on board; tiny bit of corrosion on USB receptacle.

USB stable at 20V, taking 0.02-0.06A.
PP3V3_G3H stable at 3.3V.
PP3V3_G3H_RTC stable at 3.3V.
PPBUS_G3H is at 12.3V, pulsing to 12.6 briefly every few seconds.
PP5V_G3S is at 0V, pulsing briefly to 5V every few seconds.
PP3V3_G3S is at 0V, pulsing briefly to 3V every few seconds.
PP1V1_SLPS2R is at 1.1V, pulsing to 0V
PP1V8_SLPS2R is at 1.8V, pulsing to 0V

 

[2informaticos]

Both USB ports have the same behavior?
Did you test the board alone on the desk?
Also test with known good battery.

Just in case, try DFU...

 

[sekidata]

Yes, both USB ports show the same. All tests were done on just the board alone.

Just measured resistances of some rails and it looks like there are shorts (second number is diode mode measurement):

PP3V3_G3H: 60 kΩ 0.39
PP3V3_G3H_RTC: 10 kΩ 0.42
PPBUS_G3H: 2MΩ 0.48
PV5V_G3S: 1 MΩ 0.42
PV3V3_G3S: 1.5 MΩ 0.54
PP1V1_SLPS2: 6Ω 0.004 (good board: 600Ω 0.35)
PP1V8_SLPS2R: 27Ω 0.03 (good board: 5+kΩ 0.39)

 

[sekidata]

I injected 1.1V into PP1V1_SLPS2 (which only drew 0.2A) and let it sit for several hours. The only component that got slightly warm was the T2 chip. Bad news?

 

[TCRScircuit]

I injected 1.1V into PP1V1_SLPS2 (which only drew 0.2A) and let it sit for several hours. The only component that got slightly warm was the T2 chip. Bad news?

This was a bad idea. Never inject into a cpu/t2 rail.

This could be a short on any of the SLP/AWAKE rails.

An open circuit on any of the inductors near the PMU can also cause this behavior.

See more troubleshooting info for this problem on https://repair.wiki/w/A2179_2020_MacBook_Air --- " 5v or 20v on the USB-C amp meter with low amperage ; SLPS2R and AWAKE voltages/signals cycling. "

 

[2informaticos]

You have short to ground on two different power rails, wirh 2 common components, PMIC and T2.
If T2 heats, no more history about the culprit.
1.1V injected didn't affect the T2; if still was alive.

 

[sekidata]

Yup, the shorts disappeared after I removed the T2 chip. Good-bye Air.