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MB AIR A2179 No Boot

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yelrah28

New member
Hi, I have a question about a MacBook Air I'm working on. It's a MacBook Air A2179 with logic board 820-01958.

The logic board looks completely clean no signs of corrosion or liquid damage. The machine negotiates 20V over USB-C, and I've confirmed the presence of the main power rails:

5V
3.3V
SSD power rail (2.5V)

There are no known short circuits, but the MacBook won't boot or power on.

I tried forcing it into DFU mode, and was able to successfully restore BridgeOS using Apple Configurator. The restore process completed without any errors, but the MacBook still does not power on afterward.

What could be causing this issue, and what should I check next?

The trackpad haptic works BTW.
 
2informaticos

2informaticos

Administrator
Staff member
First of all, welcome to the forum!

Any history available?
What said the customer about the failure appearance?
Which big coils get voltage?
 
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yelrah28

New member
Hi @2informaticos

Customer reports the device suddenly stopped working and won't power on.

Voltage Readings:
L7400: 0.1V
L7230, L7220, L7210, L8410, L8100: No voltage
L7030: 12V
L7690: 3.3V
L7670: 5V
 
Y

yelrah28

New member
I did some digging and found out these lines. They get the exact voltages after a fresh charger plug-in then about 10 seconds, they loose power. These lines are from U7800.

Pp0v9 slpddr 0v
Pp1v2 awake 0v
Pp1v8 awake 0v
Pp3v3 awake 0v
Ppvddcpusram awake 0v


I did these test because I suspect the T2 chip is the culprit, but how come it can communicate to bridgeOS without any error.

PP1V1_SLPS2R line current is also present all the time so I've ruled out U7800 as a culprit but correct me if I'm wrong.

I'm lost and exhausted my methods here. Hoping you could help me. Thanks!
 
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yelrah28

New member
Sorry for the late reply my shop was closed on Sunday. I don’t have a known-good board to compare with. I mainly repair iPhones, but I took on this MacBook as a challenge.

Here are the rails I checked:
Secondary power rails:
  • PP5V_S5: 5.0 V
  • PP3V3_S5: 3.3 V
G3H and T2 PMIC rails are good.
G3S rails:
  • PP5V_G3S: ~5 V
  • PP3V3_G3S: ~3.3 V
  • PP1V8_G3S: ~1.8 V
  • PP1V8_PRIM_PCH: ~1.8 V
What stood out are the S3 (RAM) rails:
  • PP1V8_S3 ~ 0v (Diode mode 0.183)
  • PP1V1_S3 ~ 0V (Diode mode 0.010)
  • PP0V6_S3 ~ 0V (Diode mode 0.350)
All three have no voltage.
  • PP1V1_S3 makes a beep sound when probed.
  • PP1V8_S3 shows very low resistance to ground.

Is that normal? I haven't tried a new charged battery. I will have one in couple of days to test it.
 
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yelrah28

New member
The online readings for pp1v1_s3 and pp1v8_s3 are abnormal compared to my current readings, and both are linked to the CPU. Could this mean the CPU is the issue? I already tried a new battery today, but nothing changed. Apple Configurator gets stuck midway—no error, just a lock icon appears, and nothing else happens on the machine.

I injected 1V into the beeping line, but my DC power supply didn’t react or detect a short. No heating component under thermal cam.
 
2informaticos

2informaticos

Administrator
Staff member
1V injected into 10 ohm load, will not cause real heat on the board; 100mA -> 0.1W.
Using performant thermal camera, you may detect small temperature difference.
Must remove CPU heatsink first.

I bet CPU is the culprit; according with low resistance on 1V8_S3 too.
 
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