since its a crappy mk cab just gut the thing, and start from scratch.
i cant stand to see a good arcade monitor wasted on a mame rig
you will end up with a better working mame rig and then you can use a nice 19 inch or larger crt pc monitor that way you can actually read the text on your menu and when you need to enter windows to update things
and the jpac and arcade vga are stupid expensive
i use the key wiz from groovy game gear they are 25$ for the solder version or 35$ for the screw termnial version
http://groovygamegear.com/webstore/
list of thingsneeded
1. wire
cheap or free if your cab still has plenty
2. key wiz
25/35$
3.nice old crt pc monitor 19-25 inch
i get mine for 5$ each from a local computer recycling warehouse
4.pc (at least a 2 ghz p4 with 512 of ram and a 128 mb graffix card)
again i getmine at the local pc warehouse usually around 40-50$
5. set of cheap 6 $ computer speakers (make shure you can cut the speaker wires easy so you can splice the amp into the speakers already in your cab )
then you need a few momentary push buttons(so you can turn on the pc without having to screw with opening the machine
3$ at radio shack
and 2 20 cent wall outlets
im working on this one now just got to do some wire mangment and install a monitor bezel
its not like your machine is a classic just a cookie cutter mk cab