trag and techknight thank you both for your input.

I've looked quite closely at both logic boards when I was cleaning them and I see no evidence of either leaked electrolyte damage or damage to any of the pcb connections. That's not to say there isn't any there, I just don't see any. Neither did I see any evidence of failed or failing capacitors, but again that's not to say they haven't or aren't failing.

I also find it rather curious that both non-working machines, the IIci and II are both showing identical symptoms, the psu firing up, the screen rasterising and then nothing. That does rather suggest that whatever the problem is, is affecting both machines.

I'm not sure where that gets us really!

Cheers!