Black screen no chime

[Danwilderspin]

You may have seen my other post where I talk about swapping out the displays from an 8,1 imac to a 7,1 well I went ahead and swapped over the screens ( and while at it the dvd drive too as the 2008 was a bit better)

so first of all I put back together the 'bad' mac (with the fans spinning and suspected bad logic board).

I fired it up and still with the fans spinning she booted up fine straight into Yosemite albeit with a slightly yellowy screen so I was happy at this point...

This is where it goes wrong

So then I reassembled my 7,1 with the odd and display from my 8,1 that id swapped...

Now it doesn't boot or chime, just the fans spin at a slow speed I only have 3 leds of the 4 lit as well

I then read online this could be a psu fault... its not as I stole that from the otherone to test...

Im at a real loss as to what to do now from having two decent imacs less than a week ago I have none any help would be great?

 

[Danwilderspin]

Just swapped the graphics cards between the 8,1 and 7,1 8,1 boots just fine 7,1 just has the 3 leds on it still im really stuck I don't know whats left except the logic board but I don't understand how I could break it by disconnecting just the lcd tem sensor and the lvds cable

Now I have two imacs by the looks of it both with bad logic boards any ideas what else I could try?

Thanks in advance

Oh yea and now I have put it all back to how it started this morning and still no dice