So... Now I've got an honest to goodness blank screen thanks to a forum member.
I started by attempting to power up the unit. No go. But I tested the smaller board's components and to my surprise, everything checked out ok. So I plugged it into my larger board:
What! Dual climate and Territory profile loaded! Well, I knew it was from a Terry.
Doesn't seem to be any differences between mine (top) and the donor one, except mine wasn't passed by Mr.B:
But it must contain the EEPROM containing the type of car and other settings.
Plug my smaller board back in and power it up:
Ah, back to normal.
Time to pull the larger board out:
First pass at testing any differences, red values are my working board and yellow values are the non-working board (this is the back-light circuit, the first thing noticeable as not working):
Ok, they look very different - however, when I power mine down into sleep mode, all these values end up being the same as the yellow ones. It looks like something is preventing the broken board from powering up (maybe U208 MAXIM 6894E - Volt Supervisor Sequencer - which will be next to check, another day though).
But I plugged in a 9v battery to the screen back-light... White screen. No lines. I powered down the unit and restarted it, very slight lines, but they went away very quickly - back to plain white screen.
Tested out all the other regulators I listed above - they all checked out ok.
Tested the tri-regulator (800mA) I hadn't tested before and I got A: 3.14v bad, 3.34v good, B: 1.54v bad, 1.75v good, C: 1.98v bad, 2.20v good - then powered down the good LCD and it read all the same lower voltages as the bad one!
I have looked for the 21v power source (there's one on the smaller board, but I can't see it being passed to the larger board) but am yet to find it on the larger board. I also tested out the LCD bias generator - it seems to get all the right voltages coming in but reads all the same voltages as my unit in sleep mode too.
Anyhoo, that's enough for tonight!