Update from today - I went to Apple Authorized Repair center. They DID manage to run Apple Diagnostics Tests (unlike how others and myself have reported this is not working from Cmd-D) - it showed no errors from top level view. They then tried various boots and installs which all stalled as have mine at home.
They also tried to use a ROM update tool (non-public) to update from my 2126.96.36.199.0 ROM to latest compatible - I thought this was going to be 2188.8.131.52.0 - but when I got home I found that it hadn’t updated from 2184.108.40.206.0 :( What I really wanted was to go to back to last known good version before my upgrade - but they said the tool can only upgrade - not downgrade.
So no fixes to my startup issues related to Kernel Panics in Windows Server - so a strong suspect is the faulty GPU (even though High Sierra booted with GPU with an older ROM before I upgraded to Mojave)
I hate the idea of junking the whole iMac because of a SW/HW incompatibility introduced when I upgraded old ROM during failed install of Mojave
One of the weirdest things is that the shop also managed to get my internal drives up and running and recognizable by Target Disc Mode - they then erased and set them up as HFS+ drives (128GB and 1TB SSD).
However - when I got home I plugged into my 2018 Airbook with Thunderbolt 2 to Thunderbolt 3 /USB-C Apple adapter - and I still see nothing. I will try with neighbor’s old macbook Air with TB2 and see if that can see them… Why would a new macbook Air with Mojave 10.14.5 not be able to see these drives?
So I have a couple of options:
- Remove the 1TB SSD (and new 2x8GB Kingston HyperX RAM I just
bought). Could also try to resell the refurbished PSU I just bought
- Buy a refurbished logic board for $500 and fit myself.
- Hang onto setup and keep hoping there is a SW/Firmware solution that
someone finds in the future. Meanwhile I could buy a new iMac… I
really miss having a ‘family’ computer for photo editing in the
kitchen which isn’t a noisy slow ancient windows machine (which is
what I replaced the iMac with for the moment)