Update:
I tried to repair mine, with 2 (so called) "Repair Kits", from eBay sellers.
Neither worked, so, on the 3rd try, I found a seller who had a "New", complete LCD, Digitizer & front Bezel (plastic still covering the front & buttons).
It worked, but, at first the color was not quite right.
The bottom line is, that it could also be a connector problem, that was the issue with the color. The connector's flip tab that holds the cable in place was broken, and not pushing the flex cable up to make proper contact inside the connector. This is ZIF (zero insertion force) or, LIF (Light insertion force) FFC style socket. We could really use a part number, or access to this, as a repair part. Because, this too, could also be the reason the Backlight doesn't work.
I managed to wedge the cable, so it works proper again.
But, I really want to replace this socket as soon as possible, without buying another dead EVO..
So, I've finally got a very expensive, But, Working EVO 4G again.
I also went ahead and tore apart the old LCD to get to the LED's used as the backlight, and found 1 was open. The 8 LED's, are a series fed string. It takes 3v DC to lite one up, so it would take around 24 v DC to light all 8.
For the fun of it, I used 6 of the old LED's, and made a flashlight, using a 3 x 3 (series/ parallel) array , a piece of polished Lexan plastic, and a 9 v battery. It's very bright!!!
hayj,
You could check the power button, if it's broke loose from the board, re-soldering it is not too hard, just watch the position.
If it's physically broken, the only place I know to get another one, is a broken HTC ERIS, it uses the same switch, for volume control.
IM