A2141 820-01700 Power cycling (DFU worked ok)

[mon2]

Hi. Working on an A2141 that is power cycling. Powers up fine (20V @ 3.1A peak) -> fan spins ok and then at a higher speed (after we removed the trackpad so the sensors are missing) -> chimes ok but after the high fan spin -> power cycles and repeats this loop. We did manage to DFU the unit with revive mode (4/4 steps completed ok) -> resulted in a brief padlock graphic before power cycling. Unable to toggle the keycaps led since the boot does not reach this far of the cycle.

Q: Does the DFU process validate that the nand flash is OK ? We do not wish to restore this board which will nuke the client's data. Perhaps the NAND flash is corrupted and causing this power cycling? The display is defective from user's CAM privacy shutter crushing the panel.
Q: Could this be a corrupt bios fault?

Tested SMBUS / I2C lines are not shorted.

Currently in chat with Master Liu (Shenzhen) who is able to extract the required client'd data if the T2 and NAND flash devices are not defective. We know that the T2 chip is ok since PPBUS_G3H is @ 12v6 (normal voltage). Cannot comment on the condition of the NAND flash but they are not heating up nor with a super low resistance on their power rail -> their power rails at a normal voltage to ground.

Welcome all comments before sending in for repair to Master Liu whom we suspect will remove the T2 + NAND FLASH off this logic board and transplant onto a working donor board. Not a fun process.

[anhbanxoi]

If you can revive the device in DFU mode mean SSD is ok and 12.6V in PPBUS also indicate good T2. You could try to reflow the RAM chips or try holding T when press the power button to boot it into target disk mode and copy data from there.

[mon2]

@anhbanxoi, thanks so much for your advice. It worked!! The client was very nervous about sending off the logic board to China although we have faith in Master Liu so we kept testing.

Your suggestion worked and the details are as follows:

1) LCD was damaged so that did not help.
2) We removed the trackpad during the logic board removal process to validate if the battery pack was a fault. New battery pack behaved the same. The missing trackpad caused the fan to spin into very high speed and forced a repeated power down after a few seconds. This further complicated the process. The thermal camera did not show us any faults as most of the temps were under 50 degrees before the forced shut down of the logic board.
3) We re-connected the trackpad and the fan spin returned to normal.
4) Sourced a 40G rated USB cable for the 'target mode' procedure using our A1534 host system. After a few attempts of powering up while the 'T' key was pressed -> we saw the logon screen on the A1534 remote unit. The password failed to open the system but we selected 'hint' and the correct hint was displayed. This gave us further hope that the nand flash is not corrupted.
5) Due to the urgency, we purchased a known good and working A2141 with Sonoma OS pre-loaded.
6) This combination worked perfectly with the same setup and a drive letter appears -> performed the MIGRATION to effectively clone the non-working defective A2141. Client was super pleased as the data was extremely valuable to continue to run their business.

Take away - learned that this 'T' mode is an early stage bootloader that is very helpful for such cases. Local Apple store could not perform this task? They wanted to send away the unit which the client refused.

If PPBUS_G3H = 12v6 = T2 is ok and has booted.

Thanks again @anhbanxoi - very much appreciated and hope this thread helps others.

[hazar]

l have same problem fan spin max no image and no chime restore with dfu done but same
PPBUS_G3H = 12v6 = T2 is ok

[mon2]

If you have a high fan spin, then there is a fault with the trackpad or trackpad cabling. There are sensors inside of the trackpad that must be present and only then the logic board will slow down the fan spins to a normal rate. For our case, we needed to salvage the data off the original machine for a very large local customer. Other shops, including Apple, stated it was not possible to save.