iMac 2011-27, white screen. Corrupted bootloader?

[herrdude]

I am working on a friend's computer. When I boot the computer, there is only a white screen. Alt/Option don't call up the boot loader. Nothing gets around the white screen. I have tried with Dosdude1 catalina loader, the OpenCore loader, another hard drive, another graphics card (even a k1100m modified card!), another inverter board, LCD screen. Nothing will get the boot loader to work. This has me quite confused.

Help!

 

[Fishrrman]

2011's have a reputation for GPU failures.
Could this have something to do with it...?

 

[Roman78]

Hey.. what tha...

Hmmm do you hear the booting sound? If not it could be the Bootrom.

 

[chscag]

Sounds like a failed GPU or a bad logic board. How did you substitute another graphics card and was it the correct one?

 

[xanderon]

i have the same problem right now with a 2009 iMac and two K2000M cards flashed with nicks bios. chime, just white screen and PRAM reset are working. but nothing else. same iMac with 4670 AMD and save boot is still working. so its not the logic board or EFI rom. its something with the cards. I ordered an external usb bios programmer, lets see if I can get this thing working again

 

[herrdude]

Sounds like a failed GPU or a bad logic board. How did you substitute another graphics card and was it the correct one?

I tried two cards (the original and a K1100m) there is no difference.

Hey.. what tha...

Hmmm do you hear the booting sound? If not it could be the Bootrom.

There is a the boot chime, there are four diagnostic lights. But the screen is always white. The boot loader never gets to the bootable partitions.

 

[Roman78]

So it could be a defective Bootrom. This mostly happens running an systemupdate of OSX including a firmwarupdate which failed. You need a CH341A programmer to read the Bootrom and verify it using UEFITool.

 

[herrdude]

So it could be a defective Bootrom. This mostly happens running an systemupdate of OSX including a firmwarupdate which failed. You need a CH341A programmer to read the Bootrom and verify it using UEFITool.

Thanks! I have ordered mine. It should be here tomorrow.

PS Cool avatar dude!

 

[herrdude]

So it could be a defective Bootrom. This mostly happens running an systemupdate of OSX including a firmwarupdate which failed. You need a CH341A programmer to read the Bootrom and verify it using UEFITool.

I dow

I was able to read the bootrom, how can I verify if it is corrupt or not?

Thanks!