Apple (Houdini II) DOS Compatibility Card Blank Screen Issue - Solved!

[MrFahrenheit]

To save someone else the trouble of trying to get video to work on a Power Macintosh 6100/60 or 6100/66 with the Apple DOS Compatibility card installed, I'm posting my solution here:

I tried 4 cards, 3 computers, different versions of the PC Setup software, different original "y" cables, with and without RAM SIMMs, etc. Nothing seemed to work. As a last resort, I swapped out my third party monitor (which is using an Apple RGB to VGA adapter) with an Apple 14" trinitron display from the era, 640x480 @ 67hz.

My DOS Compatibility card switched over and instead of seeing "no signal", I instantly saw the RAM test and it booting into MS-DOS.

If you're also experiencing blank screen from switching into the DOS card, it may be an incompatible monitor that is causing it!

 

[killvore]

Very cool! I am seeing the same thing on the same configuration (PM6100/66 w/ DOS compatibility card) connecting to my Eizo flatscreen does not give me an image. The screen is kind enough to tell me what the issue is:

So it seems the signal refresh rate is out of range for this screen. I have had this card working in my Quadra 700 when connected to an Apple CRT, though, just haven't dug those out to test yet. Would be great if there was some way to modify the output or run it theough something so it can output to a more modern screen, when the CRTs eventually die.

(The DOS card doesn't work with the Portrait Display either, sadly )

 

[Byrd]

I'm not nearby any vintage Macs, but if you hold down option on the greyed out monitor section section in the DOS Compatibility control panel, it will let you select other resolutions. However, I can't say it seems to do much the Mac will "fade out" but the CRT won't switch over to DOS. Maybe some future whiz can add more refresh and resolutions to this to match modern displays?

 

[killvore]

It definitely works on my Multisync monitor, so this seems to be on the Eizo's (and other flatscreens) inability to read the video signal. Now I want to find out if modern flatscreens with support for higher refresh rates can work