That old chestnut - SOG - Printable Version
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That old chestnut - SOG - Jacques - 05-31-2020
So, my O2 displays 1440x900 on my HP Elitedisplay really well, however I know this display is not SOG tolerant. For some reason it won't display 1280x1024_60 well, the image is offset, probably due to CRT timings in the VFO.
Has anybody tried building a sync stripper as per the link below? I'm keen to try but have no electronics / board layout knowledge and don't quite follow how the board is suppose to be laid out.
Instructables PS2 SOG
It would seem that this stripper could also apply to VGA in -> VGA out, stripping the sync signal from the green channel with the LM1881. I like the idea of placing a pot inline to adjust for variances between machine signal output.
The parts are really cheap, the LM1881 is £2.60 on RSonline, the rest come to about £2 in change.
Have time, have the money, just not the build know-how....
Actually, if there is already H+V sync from the O2, surely all that is required then is the diode and pot to change the voltage? (This clearly shows I know nothing about electrical circuits etc.!
)
RE: That old chestnut - SOG - Jacques - 05-31-2020
(05-31-2020, 11:03 AM)JacquesT Wrote: So, my O2 displays 1440x900 on my HP Elitedisplay really well, however I know this display is not SOG tolerant. For some reason it won't display 1280x1024_60 well, the image is offset, probably due to CRT timings in the VFO.
Has anybody tried building a sync stripper as per the link below? I'm keen to try but have no electronics / board layout knowledge and don't quite follow how the board is suppose to be laid out.
Instructables PS2 SOG
It would seem that this stripper could also apply to VGA in -> VGA out, stripping the sync signal from the green channel with the LM1881. It looks like the sync is stripped out by the diode....
The parts are really cheap, the LM1881 is £2.60 on RSonline, the rest come to about £2 in change.
Have time, have the money, just not the build know-how....
Actually, if there is already H+V sync from the O2, surely all that is required then is the diode and pot to change the voltage? (This clearly shows I know nothing about electrical circuits etc.!)
RE: That old chestnut - SOG - Jacques - 05-31-2020
This thread probably belongs in Hardware! Sorry...
RE: That old chestnut - SOG - kaigan - 05-31-2020
(05-31-2020, 08:00 PM)JacquesT Wrote: This thread probably belongs in Hardware! Sorry...
The Hardware forum works. Moved per your request.
RE: That old chestnut - SOG - Jacques - 06-06-2020
This does work, however I'm getting ghosting on the white areas. I think this can be made to work but it certainly removes the green tint.
RE: That old chestnut - SOG - CB_HK - 06-12-2020
Assuming that the O2 is outputting the same signals as all other SGIs (except for a few specific GFX options like Reality Engine) then both the Horizontal and Vertical sync signals are capable of being passed. I've built a handful of 13W3 adapters that route the H+V sync signals correctly to HD15 and have been able to use my SGIs on all types of displays, including plenty which do not support SoG. Although, I will caveat all this by saying I have not specifically used an O2 or attempted to change its sync settings.
As for SoG itself: you shouldn't have to strip the sync signal off the Green channel. Even with it active, your display should be able to read the sync data from the separate lines. IF you happen to have a display that is finicky, you can attempt to manually adjust how your GFX option sends sync data.
You can adjust how the sync signal is sent by using the setmon command: /usr/gfx/setmon -s n
From the man page on setmon:
-s syncselect
Specifies the source of the sync signal. syncselect is any
combination of r, g, b, and a to represent the sync signal on the
same combination of the red, green, blue, and alpha video cables.
If syncselect is n, the sync signal will be generated on the sync
cable. If syncselect is not specified, the sync signal will default
to the green cable.
Hopefully that will help solve some of the issues you're running into. If anyone else has more insight or other experiences, please chime in!
RE: That old chestnut - SOG - jan-jaap - 06-12-2020
Monitors can either
- Support SOG.
- Tolerate it (require separate sync, but at least show correct colors in the presence of SOG).
- Not tolerate it (green tinted picture on screen, loss of sync without separate sync signals).
I've messed with the syncselect option, but IIRC this either doesn't (always ?) get stored in NVRAM or doesn't survive a reboot. So you can include in in a boot script, but you loose the PROM console.
In the end it's better to do your research before buying a screen, and paying a few bucks extra maybe.
RE: That old chestnut - SOG - Jacques - 06-12-2020
My Hp EliteDisplay works fine with O2's seperate H+V sync signals, it has green tint though due to the additional signal onto on the green channel.
My Dell (had to put it in storage as my work kvm is DP only) works fine, even with SOG.
RE: That old chestnut - SOG - callahan - 06-12-2020
My older Dell 1905FP has a green tint with the O2 while the newer/higher end U2412 works perfectly without a tint.
Both monitors handle SOG without issue.
RE: That old chestnut - SOG - Irinikus - 06-12-2020
(06-12-2020, 02:27 PM)callahan Wrote: My older Dell 1905FP has a green tint with the O2 while the newer/higher end U2412 works perfectly without a tint.
Both monitors handle SOG without issue.
I guarantee you that if you use a cable with this pin pushed in with your Dell 1905FP, it will work perfectly. You just won't be able to use the cable with other machines, after the mod is performed.
![[Image: Mpj1HAa.jpg]](https://i.imgur.com/Mpj1HAa.jpg)
Here's a pic of my O2 running with the cable modded in this way:
![[Image: R8NDRN1.jpg]](https://i.imgur.com/R8NDRN1.jpg)