by Spike Tsasmali

You have a PC running MAME. You have your favorite games. You have a game cabinet. But how do you use a standard Wells-Gardner or Electrohome-style monitor with your PC? If you are running MAME, here's how to do it....!

A Little About VGA and Video Game RGB

VGA is the type of video used by most modern PC's. NTSC Baseband is the type of video used by most arcade machines. The arcade monitor is actually the same thing as a regular home color TV without the tuner and video processor circuits. Although both monitors are electronically similar, the operating frequencies differ and thus make these monitors incompatable.

VGA video consists of these signals:

Red
Green
Blue
Positive Vertical Sync
Negative Horizontal Sync

NTSC Baseband Video consists of these signals:

Red
Green
Blue
Negative Composite Sync

Here are the differences in these two formats:

VGA R,G and B signals are 1.2v p/p whereas NTSC baseband is 2.2v p/p.
VGA creates non-composite sync and dual phase, whereas NTSC uses composite sync single phase.

To convert true VGA to NTSC, you would have to do a frame capture and a "time base correction", or play back the captured frame at a slower rate to match the NTSC standard, throwing away extra frames in the process. The result is a distorted picture and a loss of resolution.

Converting VGA to NTSC for MAME

Here's the Good News....

Fortunately, the MAME software comes with a switch that automatically outputs the video in NTSC "picture" format, so there is no hardware necessary to translate the image from one format to the other. The PC will do that for you. All you do is use the -ntsc switch in the MAME command line. Here's how to use the MAME command line to do this:

Example: Pac-Man in NTSC mode

From your \mame directory...
\mame\mame pacman -ntsc

If you do this while a regular VGA monitor is plugged in to your PC, the monitor may go off or display the picture stretched or distorted. It also may damage your PC monitor due to the frequency change. So don't type in this command line until you have a game type RGB monitor connected to your PC!

Now for the Bad News...

Video cards used by PC's output the R,G and B signals too weak for most video game monitors, and they do not produce the composite sync used by game monitors. A small interface board with video amplifiers and sync mixer is required to finalize the task.

More Good News....

Here is a really nifty cure for the hardware requirements. You can build a self-powering three-stage RGB amplifier and sync mixer from parts in your junk box! This single-sided PC board is small and easy to build and will boost the weak RGB signal to strengths required by game monitors and will combine the non-composite sync into composite sync.

Schematic of MAME RGB Interface

You will need to Download the PC board and Schematic File mamergb.pcb from the Lupine Systems Download site. The single-sided layout is on the BOTTOM LAYER and the Component Placement Guide as well as the Schematic Diagram are on the 1 Mid Layer. If you need help making the PC board, read the article, "Making Printed Circuits". Remember that all PC board layout files on the Lupine Systems website are in Easytrax format, so if you haven't installed Easytrax, you will need to Download Easytrax and install it before you can view or use the PC board layouts.

Once you have the PC board assembled, use a VGA to VGA patch cord (available at Radio Shack) to connect the Interface Board to the PC. Or, if you don't mind the project hanging out the back of your PC, you can use a 15-Pin High Density D-Sub Gender Changer to mount the converter to the back of the PC directly to the VGA connector. Then use standard Molex Series KK .156" header connectors to connect the R,G,B,GND and /CSYNC signals to the game monitor.

This project can easily be assembled on the simple single-sided PC board provided in the layout file or can be breadboarded using Pad-Per-Hole board. Although all of the parts you need can be purchased at Radio Shack for less than $10 you will most likely find most of the parts you need in your junk box.

PLEASE NOTE:This project is intended to be used in conjunction with the MAME emulator software available from the MAME website at www.mame.net. This project will NOT WORK to convert VGA video to NTSC with applications other than MAME.

Lupine Systems offers a complete parts kit including PC board for this project for only $29.95. Just send an E-mail to WOOFY for more information!

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