exxos's Atari, Amiga & retro forum

Hi all,

(Posting this in Electronics since there might be an electrical reason to do with monitor detection)

I have been using an Extron DVS-304 to convert VGA to DVI for various devices, including my SGI o2: This device works fine, except it has some issues with whites/greys (white isn't white enough, and there seems to be limited grey) So I started looking for a newer model scaler.

I found the Extron DSC-301 HD: This device is much newer and it's output quality was much nicer, better whites and greys! Except it didn't seem to work with my SGI o2. The o2 seems to know when it is connected to a monitor, and for whatever reason, it did not detect the Extron. When the o2 does not detect that it's connected to a monitor, it boots to a basic login screen and refuses to load a GUI desktop: So I decided to try a different Extron scaler, I managed to get an even more professional model, the Extron IN1606: This model is especially nice since it has two VGA inputs and 4 HDMI inputs, very versatile. But again, the SGI o2 still does not think it is connected to anything and won't boot properly, same as the DSC-301HD.

When plugging the o2 directly into the monitor, all is fine. I tried logging into the web GUI for the Extron and played around with the EDID settings, I generally tried setting it to 'EDID same as output', so it should replicate my NEC Multisync monitor's EDID. But this did not help. I also tried setting the EDID to a custom Extron EDID, but this did not help either.

Example of the Extron GUI (not indicative of my actual settings): At this point I am very confused, I am hoping that this could be solved somehow inside the Extron configuration. Or is there an Electronic method I can do to trick the SGI to think it's properly connected to a monitor? Does anyone have any idea? Please also bare in mind that SGI's output Sync-on-Green. I do not know if this is a factor.

Have you checked your original box manual to see if it quotes sync on green support? I assume later boxes don't..

exxos wrote: 24 Oct 2025 09:37 Have you checked your original box manual to see if it quotes sync on green support? I assume later boxes don't..

I know another person with an o2, he tells me his works with that particular scaler. Which is why I am thinking I may have some kind of electronic signal issue (I tried different cables) Also if SoG wasn't supported, I wouldn't be seeing anything, but I do see an output. Usually bad/no SoG support means you get a green-tinted display.

It be hard to know unless you can compare a working to non-working video signal. Maybe the voltage or timings are borderline and your original box just happens to work ?

I've tricked headless machines into thinking they have a monitor by supplying the 75 Ohm termination expected on the monitor side to the RGB lines within the cable itself.

Could the upscaler be doing some kind of active termination and the negative pulse of the sync on green is messing that up?

Perhaps you could experiement with a simple 3x75Ohm to ground dummy monitor connection and see if your session launches properly (checking for its processes via SSH)? Then perhaps you could simply add enough resistance into the real cable at the appropriate place to get over that hurdle.

BW

Steve, this is a long shot, but...

its possibly the case that DDC (Display Data Channel) signals are required to set the video timing.

I had a similar issue where I couldnt get (IIRC it was an Amiga) to display on a quite rare monitor when starting it 'normally'.

The workaround for me was to attach the video lead after the computer had booted, but it looks like in your case this isnt going to be possible.

Are there perhaps any changeable DDC settings on the SGI or on the scaler end you can look at?

Thx for the advice all, I'll investigate all this further... ps Ant, I can't see any DDC settings in the web-ui unfortunately.