Well I finally got a chance to look at the 512K.
Plugged it in, bong,...... nothing on the display.

Looks like I'll need to crack it open and take a look at the analog board and see what's up.

Click to expand...

First check the overlooked dim dial. It can be turned way down, easy to do when handling actually. Second, give it a smack on the left side. You might get a flicker of life or it may stay on - but if it does, turn it off. It means there is a cracked solder connection. This is very, very common and easy to fix. The most common areas for solder cracks are where cables enter the board. The plugs. They LOVE to crack. Same applies to the motherboard. Though less common, they can crack here too. Some quick soldering will take care of it. The problem is that if you get the screen to work after smacking it, the solder joint can arc just a bit causing a lot of heat and thus melting/burning the plug.