Crazy thought... Is it possible that you are using the 5v from GI for one of your boards?
IIRC, video mode has GI off. If so, that explains why the DMD turns off during video mode.

The video mode has a couple caviets:
Its controls are crazy stupid.
Its ugly as hell.
There is a "slow-motion" bug that activates if you capture last node on 0 seconds.

What it does have is an Extra Ball light on second stage. That alone, is worth it all. Very satisfying to earn EB.

I seen a vid with one. I'm sure it helps, but I believe that up n down become reversed once your "node" hits the top or bottom wall. Maybe its just me and my brain during this mode, but if I'm right, the joystick would still act funky.

I'm still wild guessing that someone might've grabbed the GI 5v to power that newer DMD. Did you check on that?
An easy way to check is to go into settings and check your GI power levels. If the DMD turns off when GI is off, then I'm probably correct.

Tests -> T.6 Gen'l Illum

After you enter it, the power level starts on 1 - that's off with LEDs, not sure if it's off with incandescents?
If your DMD is still on, then you can just quickly cycle through (volume buttons) the different GI levels, and you're done, my hypothesis if wrong. If your DMD turns off at any point, then you can actually determine which GI string it's connected to.

Ok... Does all 4 flipper button work during switch test? I figure that your glove is working properly, forward and backwards, but the only software reason that I can think of to "disable" the video mode would be 1 of the 4 flipper switches not working.