Macbook A2442 820-02098 boot and display issue

[macabook]

Hi,
have you found a solution for the probleme, I am facing same issue with A2442 that bootloop when display cable is connected, and work fine if disconnected. I can't figure out what is the problème there slight signs of liquide but no corrosion, i measured and compare with working board nothing that can be suspected. I tested the board on another known screen and it's axactely the same behaviour.
1-When i connect the display and the backlight cable, the mac shut down suddenly during chime, and did not reboot (5V on meter),i can only turn it back on by disconnecting power
2-when i connect the display only, it reboots several time and then show the exclamation mark and stay like that, when I mesure PPVOUT_LUXE it's 14V (go to 0 when it reboot)
3-when i disconnect both, the mac works fine on external display

Any help will be very appreciated

[mon2]

Remove all power Meter in resistance mode. Disconnect the LCD display connector.

Measure the resistance to ground of PPVOUT_LUXE. What is the resistance in ohms? Connect the display connector to the logic board. What is the resistance now of the same backlight rail?

We fixed an A2338 last week where the display was dark - display was not abused recently but was dropped 6 months ago. Short summary - one of the caps in the backlight output rail was shorted to ~52R ohms to ground. After a few plucks, unit was repaired. Saved the client from purchasing a new display assembly.

[macabook]

Hi, thank for the reply, I just found out what was the issue, I used the second original display I have as last attempt, I connected the display cable only. First it started to boot loop like previously and then it entered a different menu (not exclamation mark)asking to choose startup disk, after choosing the disk it worked fine. I connected back camera and backlight and all is working fine.

So I tried with the display that the board came with, not working again. The display is faulty. But what I don’t understand is why it behave the same way at first connection to the other display, because it led me to focus exclusively on the board but I found nothing.

[macabook]

I digged a little bit more by measuring diode mode on the screen connectors pin, and there is a clear short to ground on the backlight connector on the pins PPBCON_AWAKESW_BKLTCONN_ISNS, that explain the sudden shut down when display and backlight cables are connected.

I foud also why I was having bootloop even with a good dispaly, if i connect only the display cable without the backlight on the good display the bootlooping happens and this tricked me to think that the issue is on the board but was not.

Maybe when backlight is not connected it miss current sensing or other conditions that is done during boot ?

[jaglion19]

a2485 16" macbbok pro m1 promax
Hello everyone. First of all, I'm facing the same issue. The customer's screen arrived broken, with no display but a backlight. I ordered an LCD from AliExpress and installed it. The display was fine, but I cracked the screen while tightening the screws too tightly, so I ordered a new LCD. When I installed the screen, the device remained in the Apple loop with no light. I didn't observe any short circuits. The same thing happened with other broken screens. It works fine externally when the light and camera flex are attached, but the screen flex remains in the reset state. Furthermore, the light doesn't light up even when the flex is attached. I changed the UP800 to make sure, but there's still no change. The thing I noticed is that the PPVDD_DISP_AWAKESW line in ohm diode mode has an ohm of 052. If it's not higher, I have three options left: either the UP710 1V29 line is blocking voltage or not completing it. Or, if the u770 isn't one of these, the CPU display data line remains.

[jaglion19]

a2485 16" macbbok pro m1 promax
Hello everyone. First of all, I'm facing the same issue. The customer's screen arrived broken, with no display but a backlight. I ordered an LCD from AliExpress and installed it. The display was fine, but I cracked the screen while tightening the screws too tightly, so I ordered a new LCD. When I installed the screen, the device remained in the Apple loop with no light. I didn't observe any short circuits. The same thing happened with other broken screens. It works fine externally when the light and camera flex are attached, but the screen flex remains in the reset state. Furthermore, the light doesn't light up even when the flex is attached. I changed the UP800 to make sure, but there's still no change. The thing I noticed is that the PPVDD_DISP_AWAKESW line in ohm diode mode has an ohm of 052. If it's not higher, I have three options left: either the UP710 1V29 line is blocking voltage or not completing it. Or, if the u770 isn't one of these, the CPU display data line remains.

voltage lines same as a2442
Yes, I had the opportunity to make a quick observation today. It should be 112 instead of 52 ohms. I haven't been able to detect the fault yet. Two places have low ohms, one is PP3V8_AON, the voltage of this is normal 3.7V, but I measured the place where PPVDD_DISP_AWAKESW is on the working motherboard and it should be 112ohms. If one of the power integrated circuits is not faulty, there is a high probability that the line sending voltage to the display on the processor is faulty. However, I am not saying for sure, I will completely disassemble and replace the u770 and up710 and the surrounding components and try them. When I find a junk motherboard, a motherboard with iCloud installed, or a reference motherboard