Lewis Carroll's White Queen, who said "why, sometimes I've believed as many as six impossible things before breakfast" might have been the previous owner of this machine.
I finished the ColorDMD installation (without doing anything to the ROM), updated the display firmware, fire it up, and no display. I can bring up the display configuration menu, but no game animation.
So I know when working with these boards it's important to check, double check, triple check that all cables are connected correctly. The ColorDMD instructions are somewhat ambiguous (install with the red stripe to the right--is that my right or the board's right?) so at first I had the ribbon cables matching the original configuration.
On inspection I noticed the ribbon cable from the display board to the LED board has the red stripe at pin 14. Doesn't the red stripe usually go to pin 1? So I reverse that cable, fire it up, and it works!
So what, you're thinking. That the display doesn't work with a cable in the wrong orientation and works with the correct orientation isn't quite a news flash. OK, but how was the original display working with the cable in that original orientation?
In the "before" picture both ribbon cables have the red stripe to the left.
After, the 26-pin ribbon has the red stripe left, while the 14-pin ribbon has red stripe right.
The display ROM continues to have that 1 pin out of the socket, as it's been since I got the machine about a year ago. I try not to think about it too much, as long as it works.