PC Compatibility Card: No Video W/ 3rd Party Video Card (4/97)

I am having trouble using the 7" and 12" PC Compatibility Card along with a 3rd party video card.

When the 3rd party video card is installed into a Power Macintosh and the PC Compatibility Card and Mac video are daisy chained into one display the monitor does not work.

Under this same configuration, if I then attach two separate monitors (example: 17" monitor attached to PC Compatibility Card and a 14, 17 or 20" monitor attached to the 3rd party video card), everything is okay. Both sides display fine.

Why is this occurring?

The design of certain 3rd party video cards omits the ground signal on pin 14 of the DB-15 connector on their video cards. The PC Compatibility Card checks for ground on pin 14 to determine if a monitor/video card is connected.

The system won't exhibit this behavior when using two monitors because the monitor is grounding the signal on pin 14 of the PC Card video connector.
Published Date: Feb 18, 2012