No replacement screens work

I'm at a bit of a loss here.

I have a Verizon M8 Windows Phone that had a dodgy touch screen, but the LCD was fine. I purchased a new LCD/digitizer combo and installed it. No go. LCD won't light up, but the touch screen works, syncs ok, volume works etc.

So, I purchased another LCD/digitizer, thinking the 1st one might be faulty. Still no go. Same issue, no LCD but syncs ok. Touch screen ok. I can actually navigate around by taking screen shots and viewing them on the PC.

If I plug the old LCD in, it lights up fine (I cracked it trying to remove the digitizer, so can't reuse it).

So by now I'm thinking that maybe I damaged the LCD connector on the main board. So I purchased a another good used and tested Verizon main board. SAME ISSUE. No display, but everything else seems to work ok.

Am I missing something obvious here? Do the Verizon versions have their own specific screens? Do the Windows Phone versions have their own screens? I have have trawled the net and can't find any info.