Problem with VGA Output to IBM PS/1 CRT Monitor

[Gervaldas]

Hi. Does anyone here is using MiSTer with IBM PS/1 CRT monitor? I can't get proper VGA signal to my IBM PS/1 2011 (P/N: 53F5799). The monitor is connected to mister using VGA output (not HDMI). I get the rolling image where traces of menu are visible. I spent an evening experimenting and googling, but no success so far. MiSTer software was updated today as part of troubleshooting process.

The relevant mister config:

Code: Select all

forced_scandoubler=1
ypbpr=0
composite_sync=0
vga_scaler=0
vscale_mode=0
direct_video=0
video_mode=640,480,60,cvt
video_info=1
vsync_adjust=0

As I understand only the following non default settings are essential:

Code: Select all

composite_sync=0
video_mode=640,480,60,cvt

When I connect my Windows 7 PC with 640x480@60Hz (16bit colors) to this monitor it works perfectly. I believe this standard resolution should work on any VGA monitor, but something is off. If I connect MiSTer to my DELL 1703FPT LCD using same VGA output it works fine with the same settings. I wonder if I somehow could extract VGA timings from my Windows 7 machine.

The monitor is virtually the same as in this video https://www.youtube.com/watch?v=7Jt_nBugP3Y, only P/N is 53F5798, but should be the same. Video author Adrian describes and tests various modes this monitor supports and 640x480@60Hz is among those.

If it is relevant I have this prebuild model of MiSTer https://ultimatemister.com/product/ulti ... -blisster/

[FoxbatStargazer]

for most cores vga_scaler=0 means the video_mode will be ignored, and instead it will bypass the scaler and use original analog resolutions and timings. Most of those are 15khz and won't work on a PC monitor. so you need vga_scaler=1 to use your video_mode.

However if you did flag forced_scandoubler=1, that will double every analog line up to 31khz output, so that should take care of it for most cores without need of vga_scaler, including the menu.

[Gervaldas]

Yes, with 15 kHz monitors it works fine, now I want to try out old computer cores like Atari ST or MSX, which it seems on MiSTer works only on 31 kHz.

[FoxbatStargazer]

Atari ST and MSX/2 work fine at 15khz. You only need higher resolution for the ST monochrome mode. Otherwise these are largely 15khz systems and work as such connected to a CRT. If you accidently tried some scanlines/scandoublerfx options in the core settings, these will force 31khz output and you need to go disable them, either by connecting with a compatible display or deleting the similarly named config files in the _config folder.

Now ao486 or x86000, those are a different story. You can use vga_scaler and an appropriate video_mode to force 15khz modes, but its not always the full experience.

Still if you'd rather use a VGA monitor you should definitely be able to get all Mister cores running there. You just have to choose between enabling either forced_scandoubler, or vga_scaler. They are two different approaches, usually forced_scandoubler being the simpler one and its curious that it doesn't seem to work for you.

[Gervaldas]

The whole reason why I switched from my Commodore 1084S to 31 kHz monitor is that those both cores does not work with 15 kHz. All the console cores work fine, but not the computer cores. If I can run NES core for example, then it should also work with Atari ST, no? And looking at multiple posts on internet also showed that it does not work. For ao486, yes I know there are modes that would run 15 kHz.

On the other hand cores does not matter at this point, because I can't get even OSD to work on IBM PS/1 VGA.

I'm almost certain that my problem is with video mode and VGA timings.

[FoxbatStargazer]

I have both Atari ST and MSX running on 15khz CRT so something is definitely set up wrong there. MSX hardware isn't even capable of more than 15khz. As mentioned the only issue with Atari ST is you need to be running in color mode (not mono) with color software. You might have to toggle a video setting in the core's menu for color instead of mono, been a long time since I did that. There's also 50 vs 60hz for the ST, the default depends on the region of bios you use, but I would bet a commodore monitor should handle both. (Also note, the ST core won't even boot if your bios stuff is set up wrong. It can really help to use HDMI at least temporarily for troubleshooting to ensure everything is set up.)

For your PS/1 monitor I would try forced_scandoubler=0 and vga_scaler=1, and your video_mode=640,480,60,cvt. See if you can get at least the menu to come up that way.

[Gervaldas]

I've just tried both 15 kHz with Atari ST and I get the same rolling of screen. Menus and console cores work fine. With PS/1 monitor your suggested settings also gives rolling image.

So how do you connect you Atari ST to 15kHz CRT? VGA output or HDMI output? Can you share the config?

[Gervaldas]

Got Atari ST working on 15 kHz, monochrome was enabled from previous tests... Ok, my mistake with this. But PS/1 issue still exists.

[rcade]

Those IBM monitors only work at one specific frequency, and are not flexible at all. You need to look up the exact specs and force MiSTer to use it. It will not work well for any cores that don't like being forced.

[FoxbatStargazer]

Oh, I've noticed some oddness with vsync_adjust=0 with the scaler and the menu core. Like on a C1 OLED at 1080p, the screen moves left and right oddly. vsync_adjust=1 or 2 fixes it. That fetches the refresh rate from the core instead of your video_mode. Maybe give that a try.

[Gervaldas]

For now I will use 1084S for MiSTer and IBM for actual DOS PC. I've managed to force all the cores to 15 kHz, so it's fine. I will leave experimenting with IBM monitor for the future, maybe someone even implement IBM PS/1 core. Thanks for the support guys.