Macbook Air M1 820-02016 no screen (LCD_PWR_EN=0v)

[SSBDADC234]

Haptic feedback on the trackpad works, and the app configurator on other MacBooks recognizes this MacBook.(not DFU status) That is, the power is turned on normally. However, nothing is output on the screen. no backlight, no image.

Both screen and screen cables are fine.
The result of the logic board check is as follows.
PP1V8_S2 = 1.8v
PP3V3_S2 = 3.3v
PP5V_S2 = 5v
PP3V8_AON_VDDMAIN = 3.8v
PP5V_SW_LCD = 0v
PP3V3_SW_LCD = 0v
PPVOUT_LCDBKLT = 0v
LCD_PWR_EN = 0v
PMU_SYS_ALIVE = 1.8v

There is no short circuit in either of the above.
Due to a defect in LCD_PWR_EN line, UP710 chip seems to be not working properly. I replaced the UP710 chip, but the symptoms are the same.

I checked the circuit diagram and LCD_PWR_EN is the line output from the U8100 MAIN PMIC. I'm not sure if the PMIC has failed because all other power lines including VDDMAIN are normal and no short circuit has been found.

In the worst case scenario, could the GPU of the M1 have failed? If so, it would be impossible to repair, but it's scary.

[reformatt]

How do you know the screen and cables are ok? Have you tried it on another MAC, or put in a known good screen? Have you checked with external monitor via USB-C to HDMI etc?

How have you confirmed that the MAC has POST'ed?

[SSBDADC234]

How do you know the screen and cables are ok? Have you tried it on another MAC, or put in a known good screen? Have you checked with external monitor via USB-C to HDMI etc?

How have you confirmed that the MAC has POST'ed?

The speaker also doesn't output boot sound. So I noticed another issue.
When I try to restore in apple configurator, error 21 is output. It wasn't booting properly in the first place. According to repair wiki, error 21 is ROM or NAND error,

https://logi.wiki/index.php/DFU_Mode_Restore_(Macs)

(21- Resolved with SoC ROM replacement. On macbooks with an M1 processor, this error also means problems with NAND chips such as:

• Failure of one or two NANDs.
• Mismatch between the NAND model and the reference designation on the board (When replacing memory chips, you no longer need to write anything to them using the programmer, just follow the model/place on the board).
• Attempting to restore from recovery after replacing NANDs (After replacing NANDs, it is possible to restore only from DFU).)

should I replace NAND first? All NAND power lines have normal voltage.

[reformatt]

Depends on the history of the laptop. I generally physically examine the board closely before doing anything, looking for any corrosion or component damage. I've seen shorted caps on sub-rails cause weird issues.

You should troubleshoot with the power sequence first before diving in replacing anything.