I have a Tekken theme machine by Yamasa. It was working flawlessly last time I played it, which was well over a year ago. It sat unplugged since then. Now, when I power it up the video screen is blank, but the LCD backlight is still ON.
The game works normally (without the video) but after 30 seconds the alert loop sounds. No error codes are given.

Things I've tried:
The obvious key turn reset procedure
Re-seating the coin hopper and checked for jams
Visual inspection of components / capacitors / loose cables

I wanted to see if this is a common issue or noob mistake before I start taking everything apart.

Any ideas? Thanks in advance!
I'll update you guys if anything changes...