Green tinge when using IIcx with VGA monitor

[MacMan]

Yesterday I set up my Quadra 700, Acorn A4000 and IIcx with a KVM switch linking them all to a VGA Acorn monitor. I'm using Mac to VGA cables to connect the two Macs and although the Quadra 700 has no problems displaying on the PC monitor, the IIcx seems to be displaying a picture with a greenish tinge. I thought this might be an issue with the cable so I tried a different one but it still gave the same result. I even tried a different VGA monitor to no avail.

The IIcx doesn't do this with monitors designed for Macs (eg. Colour Display or Performa Plus Display), only with VGA ones. Is the Nubus video card only designed to work with Mac monitors?

It is still usable and you do get used to the green cast after a while, but it would be good to know what the reason for it is and if there is any kind of remedy.

 

[Patrickool93]

This is just a guess, as I know nothing about it, but could it have something to do with Sync-On-green or whatever? Just a guess...

 

[MacMan]

Possibly... I've heard of sync.-on-green issues with older Macs but information on this seems to be sparse.

I forgot to add, the Nubus video card is the "Mac II High Resolution" card.

 

[Charlieman]

The tinge may be an optical illusion caused by refresh rate. Try connecting to the KVM via a VGA to VGA cable plus an VGA-->Mac adapter using various settings (the video card can only deliver 640 x 480 resolution but set the adapter to use higher resolutions, so that the refresh rate changes).

What happens when you connect directly from Mac to the monitor without going through the KVM?

 

[LCGuy]

Try installing the Basic Colour Monitor extension...it is able to fix this problem on some machines.

 

[ChristTrekker]

This is just a guess, as I know nothing about it, but could it have something to do with Sync-On-green or whatever? Just a guess...

Just FYI, I had the same thing happen to me when I used a VGA monitor with my C650 before my beige G3 arrived. It was tolerable for the week or so because 1024x768 was soooo much better than 640x480.

 

[MacMan]

The tinge may be an optical illusion caused by refresh rate. Try connecting to the KVM via a VGA to VGA cable plus an VGA-->Mac adapter using various settings (the video card can only deliver 640 x 480 resolution but set the adapter to use higher resolutions, so that the refresh rate changes).
What happens when you connect directly from Mac to the monitor without going through the KVM?

I get the same thing when connecting the IIcx directly to the monitor. I tried switching resolutions using a VGA>>Mac adaptor and it gave some interesting results. The green tinge disappeared when the adaptor was set to higher resolutions, but the Mac displayed at 512x384 and at an unbearably low refresh rate. The screen was flickering so much, I reckon it was refreshing at 40Hz or maybe lower.

I also tried installing the Basic Monitor Extension, but it didn't affect the display.

The monitor in question is an Acorn (unsure of the exact model), which is basically a re-badged Philips. It dates from approximately 1992. It seems to be capable of weird and wonderful things, like it can display at 640x480, 800x600 and also much lower resolutions which are used by BBC Micros, eg. 160x256, 320x256. When switching to these low resolutions, you can here the refresh frequency of the monitor change and it gives a slight high-pitched noise like a TV (some people can here this, some can not).

The Acorn A4000 uses 640x480 for most tasks but switches automatically to lower resolutions for certain applications and games.