The HD4850 on one of my iMac 2009 failed last week.
Finally I've got the chance to use the M4000m.
Although I've done things wrong here and there, I still managed to get it work (sort of) in High Sierra.
Finished installing nVidia web driver.
Download the English (US) Quadro & GeForce macOS Driver Release 387.10.10.10.40.140 for macOS High Sierra 10.13.6 systems. Released 2020.11.17
www.nvidia.com
Tomorrow is backlight control, perhaps.
Just rephrasing my procedures (one that worked):
Devices: 2 iMac 2009 27" and a PC
1. Drill & grind the 2 pipe heatsink to fit the MXM card (Quadro M4000m). I had only 1 power drill usable, so it took me a lot of time struggling with this part.
2. Attach the card to the heatsink, thermal paste for the GPU chip, thermal pad for RAM chip, no copper shim.
3. Install the GPU + heatsink set to the iMac 2009. Power-up the machine and got the normal chime. (i.e. no short-circuit on the card)
4. Prepare the GRML USB on my Windows PC: i) GRML USB is made by
Xanderon and later modified by
The Croupier at this
post. ii) Copy the nvflash file posted by
m0bil from this
post and the vBIOS from
Santa's Little Helper from this
post (the post is about P3000m & P4000m, but he also attached a new vBIOS for M4000m & M5000m)
5. Boot the iMac 2009 with the GRML USB and ssh to it from my Windows PC to flash the new rom to the graphic card.
6. On another working iMac 2009 (High Sierra), I attached the old SSD (with High Sierra pre-installed) via USB port, then run OCLP (0.4.2) and copy the newly generated EFI folder to the external SSD.
7. Install the SSD back to the iMac with M4000m and boot from it, after a triple NVRAM reset.
8. OCLP worked beautifully. I got to High Sierra but the graphic was sluggish (lack driver). After installing the latest webdriver from nVidia, High Sierra work smoothly.
I haven't modified the config.plist, so I still haven't got backlight control. But sleep/wake was smooth.
Mac Fan Control couldn't read GPU core temp.
GPU heatsink temp is a little high at 61 Celcius (idle), but it's the slightly overclocked vBIOS anyway.