Why is it dead?

That's interesting to know, and makes sense. I think this is likely, but there's probably also something else going on as well (purely because of the other issues such as lines and the charging light not coming on--I know the lines indicate gpu and the charging light indicates onewire, but *every reading gives the expected value* and I've tried 2 different boards and heatsinks now).

I've decided at this point to abandon this repair, give the customer the money back for the screen even though that work was good (as they don't have a functioning laptop) and make them aware that the it's probable that the cheapest outcome for them is going to be buying a replacement a1466 (which the money back from the screen basically covers anyway) which I can swap the drives on for free as a courtesy.

Leaves me slightly out of pocket but with far less of a headache in the immediate term.

@donewithit You picked right on that one. I think just doing a simple data transfer with their new laptop should be fine with them.

@donewithit - Let me correct @jadonlyon here First off you really need to run the onboard diags to hopefully ID the failure, if not then the issue is external of the logic board, so while their might be a heat sink issue as well the issue is still within the display as you claim "vertical lines on screen" which is the breakdown of the driver lines to the LCD panel.

To test things you would need to run the system in Clamshell mode using an external mDP/TB display and keyboard & mouse. The reason you need to use these external devices is you need to have the internal display closed to enable the external. While you can cheat using a rare earth magnet passing it over the Hall sensor which is mounted on the back side of the I/O board in this series back side of I/O board note that component between the headphone and TB ports.