820-00281 boot issues

[No-Clean]

Board was messed with before it came to us, Mac had the typical flexgate issue, we fixed that and realized that the other place had shorted the LCD connector and it gave no image any longer after that, after replacing U9850 I got image again, but now the problem I am having is that the OS wont load all the way or worse if I boot holding ALT bot the boot loader the Mac freezes right away, sometimes even without holding ALT the Mac just shows a blank screen.

Already tried clean BIOS found here on forum, but no luck.

I cannot even try to boot from external system since the Mac freezes before even selecting the alternate disk.

 

[2informaticos]

Disconnect J9600 and try again to boot from USB...

 

[No-Clean]

Same exact behavior, with J9600 removed it also freezes as soon as the screen shows the boot options.

 

[2informaticos]

Disconnect J8500 and test with external monitor.

 

[No-Clean]

Exact same behavior, also tested with everything disconnected just the USB-C port and same thing also.

 

[2informaticos]

Can you boot Windows, or Linux?
Also try booting macOS in safe mode.

 

[No-Clean]

I don't have Windows or Linux, but when booting in safe mode there is a variation, the folder icon flashes when booting in safe mode, I tried removing J9600 and botting in safe mode, same thing happens, flashing folder icon.

 

[2informaticos]

In safe mode, remove J9600; it should boot from USB...

 

[No-Clean]

This was done also for external drive, Mac starts to boot but it reboots when the bar barely starts to load.

 

[2informaticos]

Did you have USB macOS connected, when started in safe mode (without J9600)?

 

[No-Clean]

This was done also for external drive, Mac starts to boot but it reboots when the bar barely starts to load.

 

[No-Clean]

Yes, external USB drive with macOS connected and J9600 disconnected Mac starts to boot but it reboots when the bar barely starts to load

 

[2informaticos]

I still recommend to test with Linux, or Windows.
GPU driver is not loaded in such case; will help to diagnose such issue.

 

[No-Clean]

Tested with Linux and J9600 removed, some text starts to scroll on screen but shortly after it reboots and starts over again, Linux OS never loads, I also tested that Linux install on a different Mac and it works.

 

[2informaticos]

Reconnect J9600 and start in Target Disk mode; save any data, if needed.
Then start Internet Recovery and check if is possible to reinstall macOS.

 

[No-Clean]

When starting in target disk mode as soon as the icon comes on screen the Mac freezes, same thing when trying to install the OS over internet, I am done with this Mac, thanks for help.