Note: Jamma uses combined Sync, and VGA uses seperated sync. On your hacked VGA cable, you'd have to twist both Hor and Ver sync lines together and then solder to the jamma sync line. You can use the 15 pin vga cable, just look up the pinout on google and only use the RGBHVG wires. Also you can use just one of the grounds from any of the RGB lines to connect to jamma ground (don't need to combine them all together).