MacBook Air A2337 (820-02016) - 5V, won't turn on - please help me understand why

[mkdj]

Hello everyone,

About me, my goal and the equipment I (don't) have:
I am brand new to this forum, and I am eager to learn about repairing laptops. I have an engineer background although I haven't done electronics for a while. I have watched several Youtube videos in the last two months, trying to understand how to diagnose a faulty motherboard. I have a USB-C Amp meter and a classic multi meter. No DC Power Supply to inject voltage, no soldering iron to replace components.

About my issue and my goal:
A friend of mine has a MacBook Air M1 A2337 that does not power on. He went to an Apple Store which told him to change the motherboard. He bought another laptop, and gave me this faulty MacBook so I can have fun trying to repair it. As I want to learn, this is a perfect exercise for me. I am here to share what I have done until now on this MacBook, and ask for help to continue my diagnosis. Once the diagnosis is completed, I want to ask someone to replace the faulty part for me. My goal is to understand what to do to continue the diagnosis.

This being said, now the fun part!

Troubleshooting process:
Hardware: MacBook Air A 2337 (M1, 2020). Board number 820-02016.
History: No liquid damage, no drop, nothing particular. It just stopped powering on one day, after a complete discharge. It had only 3 years of use. My friend kept it in a closet until I ask him to give it to me 3 weeks ago.

In these 3 weeks I have run the following tests:
- Measured power in the 2 USB-C ports, in both directions. It gave me 5.1V, and random A, some bursts at 0.430A, then around 0.05A, then another burst at 0.430A.
- Opened the laptop, removed the motherboard, and did my first voltage measurements on motherboard ever:

Signal name	Measuring spot		Values
PPVBUS_USBC0	CF401		Not measured
PPHV_INT0_AONSW	FF200		Fluctuates between 4.86 and 5.18V
PPHV_INT1_AONSW	FF201		Fluctuates between 4.86 and 5.18V
PPDCIN_AONSW	FF200 (aussi)		Fluctuates between 4.86 and 5.18V
PPBUS_AON	F5200		Fluctuates between 11.9 and 12.3V
PP1V8_S2	CF403		Fluctuates between 0 and 0.135V
PP5V_S2	CP941		0V stable
PP1V25_S2	C5320		Fluctuates between 0.09 and 0.13V
PP1V2_S2	C830A		Fluctuates between 0 and 0.70V
PP3V3_S2_UPC	RF283		Fluctuates between 0 and 0.134V
PP1V8_AON_MPMU	R8324		1.8V stable
MPMU_VREF_ADC	C8321		0V stable
USBC0_3V3LDO_EN	TPG087		Fluctuates between 0 and 0.02V
USBC0_3V3LDO_EN_R	RF012		Fluctuates between 0 and 0.002V
USBC1_3V3LDO_EN_R	RF112 or TPG063		0V stable
PPBUS_5VS2_VIN	CC325		Before removing the board, with AC adapted and battery plugged in: fluctuates between 10 and 12V and I hear a "clic" in the battery every second After removing the board : fluctuates between 12 and 12.3V, and I don't hear any "clic"
PP1V5_UPC0_LDO_CORE	CF405		Fluctuates between 0.05 and 0.16V
PP3V3_UPC0_LDO	CF408		Fluctuates between 0.65 and 0.82V
PP1V5_UPC1_LDO_CORE	CF505		1.586V stable
PP3V3_UPC1_LDO	CF508		3.44V stable
PP3V8_AON_VDDMAIN	CF110		3.79V stable

Then, I looked in the schematics to look for what the PPBUS_5VS2_VIN is feeding. I found that UC300 is supposed to create PP5V_S2 from PPBUS_5VS2_VIN. As PP5V_S2 is missing, I want to see if P5VS2_EN is different from 0V.

Also, I search the Internet, and found this resource: https://repair.wiki/w/MacBook_Pro_A2...w_at_5V_repair

This resource says to check PP3v3_S2 voltage at LC710, which is at the output of UC710.

So, I did another round of measurements:

Signal	Measuring spot		Values
PP5V_S2	LC320		0V
P5VS2_EN	PPC210		0V
PP3V3_S2	LC710		0V
PPBUS_3V3S2_VIN	CC721		12,3V stable
P3V3S2_EN	PPC200		1,57V stable
PPBUS_5VS2_VIN (extra measurement)	CC325		12,3V stable
PP3V3_S2 (diode)	LC710		0.257
P3V3S2_PGOOD	PPC201		0V

I notice that I have no PP3V3_S2 signal, although UC710 is enabled and that I have a PPBUS_3V3S2_VIN signal.

This is where I am stuck.

I think the next step is to look for short-circuits. But I am not sure where, and how to do that. I have measured continuity between GND and LC710 (both sides), and my multi-meter does not beep. Resistance is very high between these two spots. Also, I have measured PP3V3_S2 in diode mode (red probe on GND, black probe at LC710), and it gave me 0.257. I don't know how to interpret this value.

I interpret this situation as follows: there is no short-circuit. If there were a short, I would have had less than 1 Ohm between LC710 and ground. Is that right?

If I had found a short, I would have tried voltage injection and alcohol/freeze spray/thermal camera to find the shorted component. But now I do not know what to do. My guess is that it is the UC710 that is faulty and need to be replaced. But I am not sure at all of my diagnosis.

Also, I don't understand why one of the CD3217 has created its LDOs, and the other has not. If UC710 were faulty, I would have expected all LDOs not to be created. How do I know that the faulty component is not one of the two CD3217?

What do you think of my analysis so far, and what would you do now if you were me?

Any help or link to useful resources to help me understand would be really appreciated!

Cheers,
mkdj

[mon2]

Hi. Welcome. A lot to read but suggest the following. Remove all power. Disconnect the battery. Meter in resistance mode. Measure the resistance to ground on each and every inductor that is on the board. Each inductor is linked to a power rail. We are checking the resistance to ground to understand if there is a shorted part onboard. Post any suspects.

Also, later on, for power injection to hunt for shorted parts, never use a voltage higher than the lowest voltage. We use typically 0v6 - 0v8 while some are ok with 1v0. This is using an external adjustable power supply that will dialed to this injection voltage & say 3A-5A which should be ample to locate the shorted part (if one is found).

Recently fixed an 'unfixable' A1932 with a shorted ceramic cap that was present on the audio board. This single cap was tanking the PPBUS_G3H main power rail. Multiple shops reported to replace the motherboard. This replacement of the board would NOT have fixed this case since the fault was on a remote audio board (headphone board). The wholesale price for this board alone was $90 from Asia. After removing 5 caps (in order), the bad boy was found and unit is working as it should be.

[mkdj]

Thank you mon2 for your message and your pieces of advice.

I've done the following measurements as suggested:

Inductor	Resistance
L5230	2.2 MOhm
LC320	1.8 MOhm
LP800	1.1 MOhm
L5840	0.49 MOhm
L5820	0.36 MOhm
L5800	0.37 MOhm

Nothing suspicious according to me. If we had a short we would have measured less than a few Ohm, no?

What now?