JROK's are used to convert RGB to Composite or SVIDEO signals.
Here's their product info
http://www.jrok.com/hardware/RGB.htmlEdit: Added
What does it do ?
This unit will convert the Red, Green and Blue video signals coming out of a video game and convert it into the composite NTSC video, or S-Video, output.
It allows you to plug a Video arcade game board into a regular TV receiver that accepts video, or S-Video input, in the NTSC encoding format.
This board ONLY works with standard resolution arcade boardsets ( 15kHz horizontal line frequency )
Hope this helps,
-Goz