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SOLVED - 820-02536 A2681 M2 Air - No power 5V 30-40mA

J

jadao

Member
This one has no liquid and just died suddenly.
Inspected the board and found out C8430 dead shorted. Replaced the cap and no more short (0,442 diode mode value).
However usbc meter is still showing 5V with 30-40mA.

I noticed the rail PP5V_MPMU_BSTLQ_XW is only 2V, schematic says 5V but I don't have another board to test. I will compare with the working board I will receive tomorrow.

It looks that this signal is going or coming nowhere than from u8100.
DFU mode is not accessible.
I get 5V on PPDCIN_AON_CHGR_R
PPBUS_AON: 12,3V
PP3V8_AON: 3.8V
 
J

jadao

Member
Hello 2informaticos,

LDOs on U8100 where surprisingly all 0V:
So I checked further and noticed MPMU_BSTLQ_LX (input I guess) was 2V. PP5V_MPMU_BSTLQ_XW and PP5V_MPMU_BSTLQ were also 2V.

The coil L8430 was open with 2Mohms! I had 3.8 volt (PP3V8_AON) on one side and 2V on its other side, there was no short on both sides...
Replaced the coil, powered the board and U8100 went 100% shorted PP3V8_AON. This let me presume U8100 was on its way to die.

I replaced and reballed another U8100 from same donnour board and now I get 20V, perfectly charging and complete chime but no video no keyboard.
Now I can put the machine in DFU mode, i tried a revive only but it failed with AMRestore error 1 failed generic error message...

Not sure what I can check before dfu restore.
 
J

jadao

Member
Yes I had chime consistently, I was able to Power off and power on, when I pressed power button I had again the chime. Caps Lock never reacted and I didn't see any light on my auxiliary usbc adapter dongle.

I am editing my message, because I noticed P5V_S2 (missing the enable) not even showing a split second but the board was able to chime...
So I went back checking U8100 LDOs and I noticed PP1V8_AON was only 0,27V...14ohms shorted to gnd
All others input and output LDOs in page 39 were present except VLDO2 (PP1V8_AON)

Under thermal cam, the upper right side of U8100 where PP1V8_AON ball is present was 35 degrees C. Injected 1.5V and nothing got warm.
Out of desperation I removed u8100 and the short remained :(
I started to remove one by one around 10 chips until I found the culprit UC870.

Reballed U8100 and soldered it back, I have now only 5V 100mA. Of course no more chime

U8100:
PP3V8_AON: 3.8v
PP1V8_AON: 1.8v
PP1V05_S2SW_VDD2H: 1.1v
PPVDD_LDO20_14_8_3: 1.25V
PP3V3_S2_LDO: 3.3V
PP1V8_AON_MPMU: 1.8V
PP1V2_AON_MPMU: 1.2V
PP3V3_AON: 3.3V
PP0V855_S2SW_CIO: 0.86V
PP1V2_S2_CIO: 1.2V
PP1V5_LDOINT_MPMU: 1.5V

PP3V3_S2SW_SNS: 2.2V decreasing, diode mode OL (wrong when compared with good board 0.690)
PP1V2_AWAKE_PLL: 0V (no short, diode mode 0.370)

I am a little bit lost about PP3V3_S2SW_SNS Maybe the ball was small and doesn't make contact? At the same time, this signal goes nowhere in the board, the sensors are not populated. tried to reflow slightly but nothing change.

Should I look elsewhere or reball/replace the mpmu?
 
Last edited:
J

jadao

Member
Yes I solder back each chip as soon as I rule out it is not causing the short, then i go to the other chip.
You were right I had a problem with my stencil, it was not flat on the middle and tricked me. I reballed U8100 and solder it back:
Now it chimes and I have the support.apple.com/mac/restore with the explanation mark.
I tried a revive but it tells me the device has no more space left... I will check with customer if he's ok I go with a Restore
I will report back thanks.
 
J

jadao

Member
It is fixed, dfu error was from the AC2 machine lacking space…

Thank you for your support.


To summarize:
-5v 30-40mA because shorted cap C8430 on PP5V_MPMU_BSTLQ_XW rail
-Replaced the shorted cap but still 5V 30mA because coil L8430 was open and U8100 was not receiving PP3V3_AON
-Replaced L8430 and this time U8100 shorted out PP3V3_AON..
-Replaced U8100 and laptop was giving chime but nothing more, black screen no keyboard, dead. Because PP1V8_AON was shorted from UC870
-Removed U8100 for nothing, and replaced UC870. No more short on PP1V8_AON.
-soldered back U8100 and I am back to 5V. (My mistake with soldering stencil) with PP3V3_S2SW_SNS + PP1V2_AWAKE_PLL missing.
-Reballed and resoldered again U8100 and everything works but I have restore error message on startup.
-Did a revive and everything is good now.
 
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