Hey all, I had a long train journey today so had time for some replies, I'm back at home now but I really have to catch-up on some work before I can do any more testing. I will be checking-in here regularly though.
I look forward to reading the guides when you have finished them.
That EFIcheck is really not a problem, but if it bothers you that link should help us disable it,
the first thing to try is probably just to delete the Launch Daemon:
/System/Library/LaunchDaemons/com.apple.driver.eficheck.plist
If that doesn’t work try deleting the kext (or just remove its execute permissions)
/System/Library/Extensions/eficheck.kext
But if you want to test this remember to disable SIP & make a full MacOS back-up first.
BTW – I was not expecting target display mode to work on the AMD cards, it was not available on iMacs with those GPUs so it is not configured by their EFI, but there is still a small chance it could work on the Kepler cards using the right cables etc.
Good to have you on-board! I did some quick brightness tests a few months back using OpenCore’s ACPI injection, Clover is much more mature so that’s probably a better option, but keep that bootrom back-up handy because I heard it can corrupt the NVRAM volume. I tried naively smooshing together various DSDT / SSDT tables taken from newer iMacs but that mostly resulted in compilation errors and kernel panics - normally related to AGDC. I also got the slider to appear, it just wouldn't do anything. There's something weird going on with multiple “Device LCD” instances, and to be honest I don’t really understand how the graphics EFI injection, DSDT tables, and all the various Kexts actually interact.
There’s also the problem of the missing “MXM structure” and badly hacked DCB tables which certainly don’t match the original iMac vbios properly. Given all that, the legacy / fall-back solution often used by linux users seems to be the better option; just poking the back-light registers directly using something like setpci, but we’d need to find them first. Chipsec might come in handy here, I was playing with it to fix PCIE bridge config issues (why the AMD cards need a back-light mod?) but I gave up on brightness control months ago, those $2 PWM modules will do the trick. I’ve attached some SSDT files & random links that looked promising, but I’ll freely admit to being out of my depth on this one. Good luck with it!
Great write-up, but you have linked the wrong version of UEFI Tool, you must use 0.26. The alpha “NE” versions are read only, still very useful because they display the section & driver names instead of just GUID codes but you can’t edit using it yet. That’s one reason your screen-shot looked different to mine, but most dumps will look a bit different anyway, if UEFI Tool can open the file without a load of error warnings then the dump is probably good. Just insert the driver files before the free space in the first BIOS region, as a rule if you don't see a very long list of DXE drivers you're in the wrong section. I’d question the need to install a Linux virtual machine just to use the CH341A, the drivers are available for almost every OS, but whatever works for you!
Now I can see the photo you posted properly I’m afraid it looks like you might have damaged the logic-board, there seems to be a SMD resistor missing next to the EEPROM chip, marked R6100 (and possible damage to R6101). I think those are “pull-up” resistors for the EEPROM which is probably why the iMac won’t POST. If you are very lucky you might be able to repair it by bridging the solder pads with graphite from a pencil, you could try and “draw” a few lines to join the dots! It’s an old over-clocking trick but it has been known to work, if not I’m afraid you’ll need to get the soldering iron out, or just get a new board. I can also see the edge of the EEPROM chip package has been ground off by the clip, even the Pomona clip will struggle to hold onto that now, I suggest laying the iMac down on it’s back to give it a fighting chance. The casualties seem to be mounting up fast here, but I guess we can say they died for science, if that’s any consolation…
If you can see that text the mod might actually be working now, do you see the boot-picker by holding Option / ALT after the chime? (you must use an Apple or any wired keyboard) What is shown in About this Mac? Do all 4 debug LEDs on the logic-board light up? If you don’t post any information it will be hard for people to help you...
I suggest you remove the GPU to test and try and restore the original bootrom backup
using Flashrom, but if the back-up file is bad you are going to have a problem, what software did you dump it with? If you PM me the dump and a good photo of the EEPROM chip and I’ll have a look.
![Nick [D]vB](/data/avatars/m/1132/1132239.jpg?1552018909){kind=avatar}
