Hanterex Polostar Issues

[Andypc]

I have recently installed a PC with Mame in my Golden Tee cab. The Cab has a Hanterex Polostar tri-sync monitor. I have two issues with the monitor. In 31kHz (640x480@60hz) I get interference on black backgrounds. Its visible in low light and you can see diagonal lines moving across the screen and speckles. I installed a new shorter VGA cable to ensure it was not near any power cables and it made no difference. The second issue is that if I use "switchres" 15khz games such as R-Type are way off the the right even with the pot on the remote board turned all the way I can't centre the picture? The manual talks about a low impedance jumper that must be in place when using VGA, but I'm not sure where. Any help would be appreciated.

[Andypc]

I have checked for earth continuity all the way back to the plug and it's fine. I checked various places on the frame and the chassis frame. I even unplugged the power cable and checked the earth pin on the chassis and had continuity back to the earth pin on the plug. I took the PC out of the Cab an connected it with a longer VGA cable. Then made sure everything inside the cab (i.e. Marquee Light) was disconnected so only the monitor was on in the cab. Turned the PC on and unfortunately the diagonal lines moving across the screen and speckles are still there. So I have ruled out interference from the PC or Marquee Light.