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Sync on green question

Posted: Sat Sep 16, 2017 2:23 pm
by anderswk
First post :)

A few days I got my first SGI machine and today I finally had time to assemble and test it. It's a nicely spec'ed O2 in pretty good condition. The ebay seller did a great job of packing it and everything seems to be working, so I'm very happy.

My only issue is that everything is tinted green on my Dell 1907fp. There's no green tint on my Dell 2407wfp, but I would prefer to use the 1907fp. According to the specs, the 1907fp should support SOG, but apparently not with this O2.

The weird thing is that the colors in the PROM are correct, but as the O2 boots and the desktop is loaded, the green tint appears. So I'm wondering if it's possible to find the video mode used for the PROM and then also use that video mode for the desktop to avoid the green tint?

Edit: After restarting the O2 a few times, I noticed that sometimes the PROM also has the green tint.

Re: Sync on green question

Posted: Sat Sep 16, 2017 2:51 pm
by robespierre
From the setmon(1M) manpage:
On systems with CRM or IMPACT graphics, sync appears on the red, green and blue signals. The -s option does not affect the sync signals on these systems.

CRM is the graphics device in the O2. It has a standard VGA connector, unlike some other SGIs, but the sync signals (both separate H & V, and RsGsBs) cause problems for monitors that do not correctly filter them out, as in your case. One way to fix this is to use an Extron distribution amplifier with sync conversion: The RGB 109xi should be easily available and cheap.

Re: Sync on green question

Posted: Sat Sep 16, 2017 8:09 pm
by josehill
O2s are a little odd in that there is a combined sync signal on the DSUB15 connector's green pin (#2) and separate sync signals on the H Sync and V Sync pins (#13 and #14, respectively). It appears that true SOG displays work fine with this setup, while some displays appear to be only SOG "tolerant." The latter type display correct images, but with green tints. I have a Dell E207WFP, and it also shows a green tint with an O2.

Interestingly, the display pinout table (Table A8, page 190) in the O2 Hardware Guide indicates that green pin includes "complete sync in some modes", which suggests that perhaps there are modes that do not output sync on green. I haven't tried to figure that out, but the answer probably would lie in the "setmon" man page or perhaps the set of video format objects.

Re: Sync on green question

Posted: Sun Sep 17, 2017 8:54 am
by dexter1
Before going the conversion device route, try this:

If you have a spare old VGA cable, you can force Sync on Green by breaking off the separate H/V sync pins 13 and 14 on one end. YMMV and no guarantees, that why i suggest doing this on an old cable.

I also have a 1907FP and could not reliably either sync or lose the green tint without this modification.

Re: Sync on green question

Posted: Mon Sep 18, 2017 12:18 pm
by anderswk
Thanks for all the suggestions.

I tried removing pins 13/14 and now it seems to work perfectly. Thanks!