Problems with Macintosh 12" RGB Display and Mac IIx

[tattar8]

I'm trying to get a Mac 12" RGB display to work with my Mac IIx.  The IIx has a Mac II High Resolution video card installed, which according to this supports the weird 512x384 resolution the monitor demands.  However, I get the weird pattern shown in the attached photo.  This seems to be some issue with resolution, but I don't have an LC-series Mac handy to try the monitor with, so I can't rule out any hardware issues with the monitor.  What could be the problem here?

 

[bibilit]

I think you screen is ok, probably an issue with the card.

Had a similar issue with my own screen, unable to display anything fine from a Macintosh II series, while working properly with an LC.

 

[tattar8]

The card does output at the correct resolution -- if I power up the machine with no display attached, it defaults to 512x384, and I can attach another monitor that displays that resolution, and the Monitors control panel confirms it.  But the same issue occurs when I then connect the 12" RGB.

 

[tattar8]

So I've been playing with this, and what I've found is that it appears that the signal the IIx is putting out is interlaced, which my LCD monitor is interpreting as "480i" (it shows it as a shrunken image proportional to a full 640x480 image).  I tried it with a IIsi, and got a clear picture on the 12" RGB, but after hot-swapping to the LCD (to preserve the resolution) I got garbage on the screen, and the LCD interpreted the signal as "640x480".  So my hypothesis is that the 12" RGB is expecting a non-interlaced signal, and can't handle the interlaced signal the IIx is putting out.  The Mac II High Resolution card is supposed to support this monitor, right?  Should I try getting my hands on another card?

The other issue is that if I power up the IIx with the 12" attached, and then swap to the LCD, it seems that the IIx is recognizing the 12" as an AppleColor 13" 640x480 display.