How to run AHT with broken display on iMac?
I recently did a bunch of system updates (I was long overdue) and my internal display stopped working. On start up, the grey screen appears and then goes to black before the full operating system is loaded. I've connected an external monitor which seems to be working without issue. Every now and then when I wake up my computer, the internal display works for up to a minute then goes black again.
I've tried a couple basic troubleshooting things that haven't seemed to help:
1. Turning off the computer, unplugging and leaving for a couple hours.
2. Resetting NVRAM
3. I've tried booting up with RecoveryHD, but the screen goes black before I can make a selection.
4. I've tried running AHT but I'm either doing it wrong (holding "D" on startup) or I'm not seeing it as my external display only starts working once the OS has booted up.
I'm wondering if this is a hardware issue or a software issue or even how I can find out. Does anyone know how I can run AHT when the internal display goes black before I can do anything?
A couple years ago I upgraded to 32gb of RAM which isn't officially supported but haven't had any issues with the computer since I made the upgrade.
I'm on a 27" iMac 2009. MC507LL/A
Any and all help would be greatly appreciated on how I can resolve this issue or at the very least know the cause of the issue. Please let me know if there are any additional details that might be useful in resolving the issue.
Thanks very much!
Is this a good question?