Strange issue with ArcadeVGA and Barco 15Khz monitor

[ckong]

I have a mame PC with an ArcadeVGA (an old type, with 3 connectors, one of which is a SVideo connector). This setup is connected to a New Astro City through a JPAC, and everything works OK.

I recently got a Barco DCD 2840 15Khz monitor. At the back there is a 9 pins RGB connector.

When I hook the mame PC up to my Barco 15Khz monitor (connected by a homemade VGA2RGB cable), something weird happens:

- If I connect the VGA2RGB cable to the ArcadeVGA and the monitor, and then power on the PC and the monitor, Windows won't start up (it hangs). I don't hear any HD activity and I don't see any picture on the monitor. I know the PC isn't running properly because I also don't hear any background music from my Mame frontend.

- But if I don't attach the VGA2RGB cable to the ArcadeVGA, and then power on the PC, it does start up properly. After a minute or so I do hear background music, so I know the Mame frontend is running. If I then connect the cable to the ArcadeVGA (while the PC is still running) and power on the monitor, the frontend screen does appear on the monitor!!!

what is going on here?

[grantspain]

sounds like the cable is wrong or is missing a connection