Main > Monitor/Video Forum
Segai M21C XX hourglass screen
Zebidee:
"Ghosting" (what I call this) usually indicates an issue with signal transmission, essentially your cabling. This seems to be confirmed as when you use a console it works fine.
So... how do you connect your PC to this monitor?
trick72:
--- Quote from: Zebidee on August 12, 2022, 09:37:37 pm ---"Ghosting" (what I call this) usually indicates an issue with signal transmission, essentially your cabling. This seems to be confirmed as when you use a console it works fine.
So... how do you connect your PC to this monitor?
--- End quote ---
It is an existing mame cab. It used to have a hantarex CRT which did not have this problem. Sadly that one broke and I have replaced it with this Segai. For the rest nothing changed on the cab or PC. It has a JPAC (ultimarc) connected from VGA to DVI on the ATI display card.
I just tried using a different vga to dvi cable but it's the same. I have a second working mame cabinet and I even tried to use the video card of that one into this cabinet but even with that video card (which works fine and does not have the ghosting on the other cab) it has the same ghosting on this one. So it's not a cable issue, or even video card issue. I even tried another JPAC and even that does not solve it. So it seems the Segai CRT has problems displaying this PC signal, while it works fine with a JAMMA/NEO GEO console signal. Very strange.
So I'm not sure now this is solvable.
Zebidee:
Maybe it isn't the same "ghosting" I thought it was.
Maybe it has something to do with your video timings setup in CRT_emulator? Your Segai monitor might be very fussy.
I don't know what video modes your NEO-GEO uses, but you might look at trying different video modes in CRT-EMU (use ArcadeOSD) to see if it makes any difference.
Try using composite sync out of CRT-EMU.
Try bypassing the JPAC altogether for video. Probably need to rig up a breakout cable. Picture won't be as bright, but you'll get enough to see if the problem persists.
trick72:
--- Quote from: Zebidee on August 13, 2022, 08:18:20 am ---Maybe it isn't the same "ghosting" I thought it was.
Maybe it has something to do with your video timings setup in CRT_emulator? Your Segai monitor might be very fussy.
I don't know what video modes your NEO-GEO uses, but you might look at trying different video modes in CRT-EMU (use ArcadeOSD) to see if it makes any difference.
Try using composite sync out of CRT-EMU.
Try bypassing the JPAC altogether for video. Probably need to rig up a breakout cable. Picture won't be as bright, but you'll get enough to see if the problem persists.
--- End quote ---
I think what I experience with this CRT monitor is the "ringing artifact" which is covered for example in this thread:
http://forum.arcadecontrols.com/index.php/topic,162118.msg1713721.html#msg1713721
I see that you have posted a lot of responses there too. They are talking about putting a THS7314/7316 RGB amp between the pc and jamma signal to get rid of this issue.
So maybe I have to do this too? Strange that I did not have this problem with the hantarex monitor however and only seems to appear on the Segai...
Zebidee:
Oh thanks, I'd forgotten about that.
The THS7314 chips do a few things that may have helped.
First, they have a sync-tip clamp or DC restoration circuit built into the inputs. This moderates any voltages above or below video spec, and "clamps" the signal to the flat/bottom part. This alone may have helped improve the signal.
Secondly, they include an (optional) LPF (low-pass filter) on each channel to cut out any frequencies below spec. He used that, and the filtering may have helped.
The LPF filter also introduces a small signal delay (~100ns or so). This is negligible in gaming terms. In real terms, it would shift the RGB image to the right by a fraction, maybe 0.5mm (depends on your CRT, how big it is).
In Bubblechump's case, this delay may have been exactly what he needed to bring the RGB into line with the sync. The large resistors (25k) he was putting on the RGB inputs to the THS7314 may have affected the filter/delay, allowing him to dial it in by trial and error.
The 500R he was putting on the outputs would have reduced the amped output signal from the THS7314, back down to something closer to what the JPAC expects.
This would fit neatly with my half-baked theory that your sync and RGB signals are slightly off somehow at the Segai end. The THS7314 and the LPF filter delays the RGB slightly, brings it back in line with the sync.