Chosen Solution

Hi all! I am trying to upgrade my GPU with a Dell Nvidia GTX 770M. (VBIOS: 80.06.60.00.01) on my iMac 21.5 Mid 2011 (EMC 2428). After having installed the card, however, I do get a boot chime, fan spin, but I do not get Led 3 (and of course 4) lighting up (With the LCD mounted, no video is present). Now, I need your help to work towards the correct direction, as I am not sure of what EXACTLY Led 3 indicates. I know, as a general rule, that it indicates that “The Logic Board is communicating with the GPU”, although I would hope that you guys know a bit more precisely thant this, as: If the Led #3 lights up if ANY GPU is found, it either means: a - That I have not connected it properly b - That the GPU is broken If the Led #3 lights up only if the GPU is found AND working correctly, it could also mean: c - That my GPU is not getting recognised, maybe because of a VBIOS problem (?) but it COULD be good. Therefore, at the moment I do not know if:

  1. My video-card is broken or if
  2. The issue lies somewhere else (like if I was sold the 770M from the incorrect manufacturer, which I really don’t think being the case, unless that eBay seller put a fake sticker on the card). Of course, if I put back the default 6750M, Led #3 goes on without a problem, and I do get video with the LCD on. Is anybody able to point me towards the right direction? Thanks a lot for your help! PS This is the card, just to make sure:

For ANYBODY experiencing this: What happened was that even if the Dell VBIOS is supposed to work on iMacs, mine was for some reason not UEFI ready. It is not a big deal as it will be detected anyways from the motherboard, and most importantly from nvflash, which you’ll use to flash your GPU and make it UEFI-useable. So, if you experienced this, follow these steps: Get yourself a 32GB USB or (preferrably) a hard drive/ssd that you can connect via USB.Using Disk Utility on Mac, erase it (Use Journaled FS)On a Windows Computer or virtual machine, download the software “WinToUSB” (you NEED the enterprise version)Using disk management on that Windows computer, select the primary partition of your external drive, and right click > Delete VolumeOn the erased space, right click > Create new simple volumeJust go ahead with default options and make sure the file system is NTFSDownload a Windows 10 ISOOpen WinToUSB, select the ISO you’ve downloaded, next select your external hddChoose Windows 10 PRO (IMPORTANT) when askedYou wil be asked how to format the new hard drive. Select “Keep existing partitions”Select the already existing EFI partition as the EFI partition, and the NTFS (large one) partition as the second optionWait until the disk gets createdBoot into that hard drive WITHOUT INTERNET (you may need another iMac or to put back the old GPU to do this)Setup Windows BUT do not connect internet.-> This matters as you do not want ANY drivers to be installed by Windows for nowDo setup a password for the Windows accountOpen Windows Update preferences and opt to “pause the updates for a week”Open Remote Desktop settings and allow remote desktop connections.Rename your PC to something easy to rememberGet another Windows PC, and connect your iMac (via LAN) and this PC to the same network (preferrably, make it a local only network by disconnecting the DSL cable from the router)On the Windows PC, open Remote Desktop and insert the computer name from step 18Get the nvflash utility with the ROM for your GPU by Nick[D]vB, i took mine from die-oswalds.de/downloads/iMac.zip Now that you are in the iMac (remotely) use nvflash to flash your GPU with the corresponding ROMReboot your system when asked, the Led #3 will appear on the motherboard. You can assemble everything back. You have a working iMac with an upgraded GPU, with a working Bootscreen! (for the brightness control you’ll need to download the Brightness Slider app).

Ah! You fell into the trap! You do realize Apples MXM boards have their own micro code. So unless you know how to flash the ROM as well as have the skills to program it you’ll get a black screen, loose the boot menu actions and brightness control (thats with a non-Apple AMD board). You also realize Apple doesn’t offer NVIDEA drivers for the GTX 770M board so you won’t ever get the board to come up within macOS without patching it before you swap out the GPU board. The NVIDEA drivers Apple offers are limited to the boards the drivers where designed for, buggering them to work with your Nvidia GTX 770M is still a bit of a task. To add to it, are you sure the board is even good?