Did you combine HSYNC and VSYNC into a composite CSYNC signal?
AFAIK the GBS8200 needs the composite synchronization signal.

Have a look at this video: https://youtu.be/kHhpTq-WSJk
It explains everything quite well.

This thing needs custom firmware to be more useful. In default it deinterlaces its inputs and shows variety of artifacts due to it...

Benedikt wrote on 2020-06-16, 15:19:

Did you combine HSYNC and VSYNC into a composite CSYNC signal? AFAIK the GBS8200 needs the composite synchronization signal. […]
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Did you combine HSYNC and VSYNC into a composite CSYNC signal?
AFAIK the GBS8200 needs the composite synchronization signal.

Have a look at this video: https://youtu.be/kHhpTq-WSJk
It explains everything quite well.

Thank you very much. So let me check, if I understand it right, the board provides H/V-Signal connectors, but needs them to be delivered combined? This is so wired, why do they do so? And this would also mean, that you can't just connect VGA input either? That's really sick..... anyway, I'll try to combine the H/V-Sync and see, what happens. Thank you for the help!

Tiido wrote on 2020-06-16, 15:28:

This thing needs custom firmware to be more useful. In default it deinterlaces its inputs and shows variety of artifacts due to it...

Any info on that? Where can I get custom firmware? The board has obviously an I²C EEPROM chip, so I guess I'll be able to flash it, but I need some information about this.

scorp wrote on 2020-06-16, 15:49:

Tiido wrote on 2020-06-16, 15:28:

This thing needs custom firmware to be more useful. In default it deinterlaces its inputs and shows variety of artifacts due to it...

Any info on that? Where can I get custom firmware? The board has obviously an I²C EEPROM chip, so I guess I'll be able to flash it, but I need some information about this.

For starters, there's a follow-up video: https://youtu.be/vwKA1z8tg1g

Oh dear, it's so funny, there is a board, which tells it supports CGA/EGA/VGA etc., however, it doesn't. At least as long as you didn't added a whole bunch of logic outside..... *facepalm* anyway, thanks guys for your help, I'll see, if I can get it running.....

as it seems you learned - the GBS does NOT support TTL RGB. It supports CGA video modes just fine after they have been converted to analog RGB though

maxtherabbit wrote on 2020-06-17, 00:35:

as it seems you learned - the GBS does NOT support TTL RGB. It supports CGA video modes just fine after they have been converted to analog RGB though

What I don't understand is, why the hell is there a standard VGA input connector with separated V-/H-Sync, which doesn't work if I connect a normal VGA card to it? I mean it delivers analog RGB signal, so why doesn't it work? For me it just doesn't make any sense for the manufacturer to add a VGA connector, some resistors and simple wiring on the PCB to have a dead port. And nobody seems to use this VGA Port for anything indeed, everybody goes for RGBS for CGA and EGA. That's why I thought, that I can test if my GBS8200 is working by simply connecting VGA to it and see if the signal is coming through.

scorp wrote on 2020-06-17, 07:26:

maxtherabbit wrote on 2020-06-17, 00:35:

as it seems you learned - the GBS does NOT support TTL RGB. It supports CGA video modes just fine after they have been converted to analog RGB though

What I don't understand is, why the hell is there a standard VGA input connector with separated V-/H-Sync, which doesn't work if I connect a normal VGA card to it? I mean it delivers analog RGB signal, so why doesn't it work? For me it just doesn't make any sense for the manufacturer to add a VGA connector, some resistors and simple wiring on the PCB to have a dead port. And nobody seems to use this VGA Port for anything indeed, everybody goes for RGBS for CGA and EGA. That's why I thought, that I can test if my GBS8200 is working by simply connecting VGA to it and see if the signal is coming through.

The way I see it, the "VGA input" is basically an RGB SCART input that merely uses the more compact VGA connector. SCART uses composite sync, only, namely either via the composite video line or via a separate blanking signal.
The SCART link can save a wire that way without adding complexity to the TV set, because the TV set has to deal with composite sync signals, anyway. It has to be able to process a TV channel, after all.
The manufacturer of the GBS8200 probably just grabbed a random cheap TV scaler circuit and designed a board around it.

Benedikt wrote on 2020-06-17, 09:11:

The way I see it, the "VGA input" is basically an RGB SCART input that merely uses the more compact VGA connector. SCART uses composite sync, only, namely either via the composite video line or via a separate blanking signal.
The SCART link can save a wire that way without adding complexity to the TV set, because the TV set has to deal with composite sync signals, anyway. It has to be able to process a TV channel, after all.
The manufacturer of the GBS8200 probably just grabbed a random cheap TV scaler circuit and designed a board around it.

Yeah, you are probably right. The VGA is not VGA, but something else. However, beside that it is very irritating for the users, since they even write "VGA input" on it, it is also very confusing to see H-/V-Sync wires going from the "VGA input" into the chip. Nothing, and I mean nothing, makes you think, that this is not a regular VGA port. In real this is kind of proprietary RGB SCART connector, whatsoever. That's why nobody uses it.

The VGA input does in fact work with RGBHV if you use custom firmware. The software that comes with the GBS is absolute trash, though the device itself is quite nice.

scorp wrote on 2020-06-16, 14:38:

...I thought the GBS8200 is broken, so I got another two from different sellers and all of them behave in the same way. Does anybody here have any experience with it? Am I doing something wrong, when I just connect VGA cable and expect VGA on output? I thought I try this, because my CGA/EGA 9-pin adapters could be wired in a wrong way. However, with simple VGA to VGA I have the same issues. Any ideas?

Hehe, I have exactly the same lesson learned. Also connected a EGA (and remember to have seen a picture at the beginning). But after retrying...nothing. It was not reproducable. Therefore I assumed I made a wrong connection and destroyed the unit. I ordered another GBS but it was the same....

Thanks for the Youtube link, very interesting! But I dont think I will further beat around with this sh*** and order a MCE2VGA if I need it....

MCE2VGA is a scaler - you don't need that at all if you have a GBS

1) get the custom firmware for the GBS8200 set up
https://github.com/ramapcsx2/gbs-control/wiki … ld-the-Hardware

2) buy a TTL RGB to analog RGB DAC like this one:
https://gglabs.us/node/2063

maxtherabbit wrote on 2020-06-17, 22:53:

MCE2VGA is a scaler - you don't need that at all if you have a GBS […]
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MCE2VGA is a scaler - you don't need that at all if you have a GBS

1) get the custom firmware for the GBS8200 set up
https://github.com/ramapcsx2/gbs-control/wiki … ld-the-Hardware

2) buy a TTL RGB to analog RGB DAC like this one:
https://gglabs.us/node/2063

Very cool, this TTL to RGB converter you are talking about, it is using a GAL/PAL to switch the signals, this is the very same idea I got when watching the GBS videos linked above. Where they guy is struggling with the EPROM an so on. I thought why so complicated, if he could just use a PAL? Anyway, nice to see, that my idea was not so bad 😀 I'll try to make a prototype, as soon as I have time for it.

Here is my recent experiment with the GBS-8200 and CGA from an ISA card.

I bought the GBS-8200 a few years ago for the purpose of using with an Atari ST. I had lots of problems and never got it to display anything but a highly corrupted noisy picture. I was aware of the necessity to decrease signal levels and combine H and V syncs from the Atari to create a combined sync. I used a 74LS86. I eventually gave up.

I have an old CGA ISA card of unknown chipset. I am the original owner, so unlike some of the retro PC junk I have bought off Ebay, I at least know that it has been treated and stored well. I was intrigued to try it on a 486 motherboard. Part of the reason is I am working on a 8088 based IBM-PC clone PCB, and I really wanted to find out if I could use this card and confirm I had a way to display CGA.

So in the attached picture you can see my setup. I have used the same 74LS86 to combine the syncs (it's strange that this is needed since the ASIC has H and V separate input pins) and the TTL output passes through a resistor to the GBS. I also connect the R, G and B outputs of the CGA card through resistors, however the board does have adjustment pots, so they might not be strictly necessary - IDK. Better to be safe and use a resistor. The I(ntensity) is left unconnected for the time being.

Well the PC booted and beeped the speaker with some error code, but after some fiddling I was able to see the BIOS boot text and later I was able to enter the BIOS. Picture quality was poor. I used a scope to confirm that the Hsync was 15kHz and Vsync was 60Hz as it should be for CGA. I know that old motherboards had a jumper to select between B&W and color, which I assume that the BIOS reads and uses the program the 6845 CRT controller with either MDA or CGA register setting values.

I adjusted the three pots. I could turn red all the way off, and likewise I could turn blue all the way off, but the green input wasn't green it was displaying white/grey! That's why I wondered if the card might be in MDA (mono) mode and the GBS was detecting the MDA frequencies and switching into a MDA mode. Clearly this wasn't the case. After much fiddling I was unable to get green by itself, so I am left completely puzzled.

Picture quality was poor and there were vertical noise stripes running in vertical bands, as reported in various YouTube videos. In the picture above that is the picture with red and blue pots set to zero only allowing a signal from the green input through. So why is it displayed as white/grey? Also you can see the noise at the very bottom against the black backgroun, but you might have to zoom in.

BTW I have done the PSU regulator capacitor mod.

Also strange was that the "Geometry" menu didn't do anything, so I couldn't centre the picture. Also selecting 640x480 display mode, I just got "no signal", whereas in 800x600 and 1024x768 I at least got some kind of (poor quality) picture with readable text.

I am clutching at straws, but given that so many people have reported great quality pictures using this converter, I wonder if I have just got a bad version???

Certainly the picture is so poor and missing green, that it makes it unusable.

I'm leaning towards buying another to see if it works in the same way, or if I have better success.

Based on what I've read on various forums I suspect that the GBS-8200, with or without GBS-Control, has really poor support for actual CGA/EGA graphics (320x200). Without GBS control, it treats all analog input as 480i. GBS-Control doesn't look like it was tested much with 320x200 because I haven't heard of anyone having good results. The only way to integer scale the resolution properly is with a 5X horizontal multiplier and 6X vertical multiplier, which the GBS-Control doesn't support as far as I know. You might be better served by converting digital RGB to analog and then to a small monitor, even if that means using an older, rougher TV.