TwinTurbo 128-3D won't switch resolutions

[Forrest]

I'm using my SuperMac600 with G3/220 upgrade, iXMicro TwinTurbo 128-3D and a Voodoo 2 1000 card. I ran Quake 1 in 3Dfx mode today at 800 x 600 - ran fine. I quit the game and the screen went blank. I had to power off. I've since tried rebooting a few times and confirmed the only resolutions that work are 640 x 480 at 60 Hz and 1024 x 768 at 70 Hz. Anything else results in a blank screen, which switch the monitor into standby mode. The LCD monitor is about 10 years old and has VGA and DVI connectors. The Mac is connected to VGA. For the past 2 weeks, I was able to switch between 640 x 480, 800 x 600 and 1024 x 748 at multiple refresh rates without a problem. There screen wiggled at a few resolutions, but it's stable at 1024 x 768 at 70 Hz. I've disabled the 4 3Dfx extensions and removed the Voodoo 2 card, and zapped the PRAM once. I still am unable to switch to anything but 640 x 480 or 1024 x 768. On startup, I must disconnect the monitor power cable and reconnect before I can a picture - so it appears the VGA sense is not working. Any ideas?

 

[Forrest]

Opened the case, pulled both video cards which looked clean and undamaged. Temporarily connected the monitor to the built-in video port with a switchless Mac-VGA adapter and was able to use the computer at 640x480, 800x600 and 1024x768. Plugged both video cards in and everything now works when connected to the video cards??? I suspect some type of extension conflict when running Quake - the 3Dfx card conflicting with the 3D acceleration on the iXMicro card.

 

[Byrd]

Hi Forrest,

I tend to agree it was possibly the switching of output between the 3DFX card and Twin Turbo that muddled things up - possibly an incompatibility here.  Should it happen again you could use a KVM or try a better quality VGA cable between the 3DFX pass through and video card.

JB