I thought I'd give a little write up of the Capcom Input/Output (I/O) board as there doesn't seem to a lot of info out there without trawling through pages of forums.
For those not in the know, these I/O boards are for linking JVS pieces of hardware up to a JAMMA cabinet. There's many I/O boards out there for different uses, but we'll ignore them for now. The two most common I/O boards available for JVS to JAMMA are the Sega and Capcom versions. The Sega one tends to be a little cheaper, but lacks an onboard sound amp, lacks JVS power out, and needs spare pins mapping for the extra buttons. The Capcom board can run a Sega NAOMI from the power which it can output, but will not run a NAOMI GD-ROM drive at the same time, it simply cannot supply enough power. The Capcom boards seem to run around £80 to £100 in the UK with all of their cables.
The Capcom board is often described as the Capcom NAOMI I/O board, and I've seen quite a few people ask the question if it can still be used for other JVS hardware. The answer to that is YES it can. I've been using mine on my Taito Type X2 to play Street Fighter IV and Blazblue Calamity Trigger.
Here's what the board looks like. I got quite a shock at the size of it when I first got mine. Top left is the JVS power out connector, top right is the volume potentiometer:
Here's an image of the input side. This is where the JAMMA edge connects, as well as the Capcom CPS2/3 kick harness (so you can use 6 buttons) and Speaker In:
Next is the output side. In order from left to right you have: Speaker out (it's this side you want to use for the sound cables to your NAOMI or Type X2 etc.), an output which I have no idea about, JVS connector out, VGA out, JVS power out.
Lastly we have a shot of the cables you will want to be getting with your Capcom I/O board should you want one. Top is the JVS connector, which is actually a PC USB cable. Next is a speaker out cable, which again you may have lay around the house, a VGA cable which you might have on your PC monitor, and a JVS power cable.