Ok, so the U4 does not use EL panels.
It uses a flourescent bulb inside the light box behind the mini marquees.
Unfortunately, it's too bright, occasioanlly has a humm associated with flourescent tubes, and there's not only a ton of light bleed at the edges of the enclosure, but it also highlights all of the knocks and scratches that the mini marquee cover has taken through years of real world use that just looks crap.
So I decided to grab some EL panels from www.neogeoledmarquee.info
http://www.neogeoledmarquee.info/product/4-slot-slim-universal/
However, this cab is original, and is in largely good shape, so I'm not looking to do anything destructive, nor am I wiling to take the old bulb out and store it as it'll certainly get damaged and that will end up being unintentionally destructive.
I thought about simply unplugging the bulb, but that's hardly an elegant solution, so instead I opted to add an inline switch...
Next was to establish a way to fit the EL panels onto a cabinet that doesn't use them, and to also keep the original mini marquee holder.
Turns out that was an obvious and dead simple solution. Adhesive strips, cut to size.
Was pretty straight forward to carefully place them in front of the bulb, and although it was a pretty close fit, they all went in perfectly across the width of the mini marquee holder.
Sadly, the wires from the EL panels were not quite long enough to mount the control PCB inside the cabinet, so I needed to find a place inside the light box and still have access to the buttons and the potentiometer on the PCB itself. Again, tight, but perfectly adequate. (The feet of the PCB are also held to the cab with trimmed down adhesive strips)
It's very simple and self explanitory to wire up, and the cable between the PCB and the MVS motherboard was plenty long enough.
As I said above, very straight forward to wire up, so I was actually worried that if it didn't work when I switched it on, it was unlikley to be a simple fix but more likely a problem with either the PCB or even the motherboard. No need to worry...
https://imgur.com/gallery/jNv6BMO (<- This should be a video?!)
Quick double check on the bulb...
Safe and sound.
https://imgur.com/gallery/qymHqCW (<- This should also be a video?!)
And I think I'm done for the day.