GDM-20D11 connected to a modern PC

Alt Res

New member
Aug 28, 2021
Hey SGI lovers, hope you're all keepin' well.

So, I recently came across this monitor on eBay, I was very lucky to get it at quite a steal at £35; it was collection only which I can imagine acts as a bit of a deterrent for some. I knew the monitor powered on but beyond that my knowledge of the monitor at the time was pretty slim.

I purchased this with the hopes to use it for my Dreamcast and PC for gaming, sorry in advance if this is a bit of a sin over here so don't hate me! :3

That being said I had to turn to the CRT Collective Group for help and boy did I get it! I quickly learnt that a SOG signal was needed and that my GPU alone wouldn't suffice for getting the feed across. One member in particular drew my attention to the Extron 190F which could take my computers feed and convert to SOG (at least that's my understanding. haha)

Prior to this I had purchased what I believe to be a 13W3 Sun Adapter, after checking the needed internal pins (RGB and grounds) I clipped away the unneeded pins for its SUN purpose so it worked more like an SGI one. Now, this was a product of forum posts and further research so I think what I did was right, as well, it works haha.

I've listed below a reverse running order from the monitor to my PC:

GDM-20D11 monitor > modified SUN 13W3 adapter with RGB and ground pins remaining > VGA > BNC > Extron 190F with SOG (sync on green) ON > VGA > DVI > Computer.

I am yet to play any games on it as this was primarily a means to test it works, I'm planning to remove the rear housing to blow some dust away! Even though it's in great condition despite the logo being missing, it certainly has some dust building up inside. - Oh yeah, any replacement logos out there? haha

I was told to post over on some SGI forums as this might be of interest to some, hopefully it is.

The remote worked a treat with a fresh battery and I could calibrate it to fit everything in perfectly!

Special Thanks:

James over on eBay: Though I didn't get the monitor off him, he spent a lot of time answering my questions in helping me getting this monitor to work for my needs. (I think he has this monitor for sale too.)
Ian over at his site: Again, despite no purchase being made we shared dozens of emails geeking out about ways to get this to happen!
Alexis over at CRT Collective Group: Without their suggestion of the Extron, I'd still be right at the beginning!

All the best,


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Feb 4, 2019
Western United States
Thanks for the information! And I don't believe there is anything wrong with putting these monitors to good use, even if it is not on an SGI system. It is nice to keep them going :)
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