RGBs to 15KHz VGA?

Discussion about old graphics cards, monitors and video related things.

RGBs to 15KHz VGA?

Postby sirnephilim » 2019-9-10 @ 02:44

I'm having a problem Googling this properly as searching for RGBs to VGA ends up with a mass of craptacular converters.

Supposing I have a monitor that supports a standard VGA connector and 15KHz (Dell U2410), how would one convert a 4-RCA cable RGBs signal? Is that just connecting the pins or would I need to correct the line level, do some sync signal rearranging, or what? Supposedly the monitor supports 240p which would make it ideal for a modern display for retro consoles, old computers, etc ad nauseam so you can see how nice it would be to fabricate some adapters for, say, SCART, RGBs via RCA/BNC and so on. I'm sure it can be done, I'm probably just lacking the verbiage to know what to search for. Keep getting bogged down with results for 30KHz VGA.
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Re: RGBs to 15KHz VGA?

Postby cyclone3d » 2019-9-10 @ 05:35

What are you using that has 4 RCA cables for the RGB signal only?

Component only uses 3 RCA cables.

Usually, when you have a console RGB cable for a console, it also has two extra RCA cables for L/R audio.

I guess you could have one that only does RGB but also has an extra for composite.

Take a look here - this one is meant to plug a VGA output into a component input:
https://www.monoprice.com/product?p_id=2173

So looking it up, you need a decoder to go from a component input to a vga output since the sync signals are combined with the RGB signals in component RGB.

Here are plans for a converter.. not seeing anything specific that supports 240p that is commercially available:
https://sites.google.com/site/tandycocoloco/rgb2vga
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Re: RGBs to 15KHz VGA?

Postby derSammler » 2019-9-10 @ 07:48

What are you using that has 4 RCA cables for the RGB signal only?

RGBs = Red, Green, Blue, Sync. That's something the NEC PC Engine for example outputs on its ext. port.

VGA requires H-Sync and V-Sync, so a simple cable won't work. You need a converter. I'd use a cheap GBS 8220, which will also remove the need for a 15 KHz-capable monitor.
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Re: RGBs to 15KHz VGA?

Postby Benedikt » 2019-9-10 @ 09:13

derSammler wrote:VGA requires H-Sync and V-Sync, so a simple cable won't work. You need a converter. I'd use a cheap GBS 8220, which will also remove the need for a 15 KHz-capable monitor.

Alternatively, you could build a Sync Signal Separator like this one.

If you are really lucky, though, a 15kHz-capable monitor might have been built with SCART compatibility in mind and might be perfectly fine with composite sync.
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Re: RGBs to 15KHz VGA?

Postby sirnephilim » 2019-9-10 @ 10:42

Benedikt wrote:
derSammler wrote:VGA requires H-Sync and V-Sync, so a simple cable won't work. You need a converter. I'd use a cheap GBS 8220, which will also remove the need for a 15 KHz-capable monitor.

Alternatively, you could build a Sync Signal Separator like this one.

If you are really lucky, though, a 15kHz-capable monitor might have been built with SCART compatibility in mind and might be perfectly fine with composite sync.


Thanks for the info. I think there's at least a reasonable chance of SCART compatibility given the standards supported but we'll see.

And looking for 15KHz compatibility was more in line with supporting old computer RGB standards along with consoles; I have an OSSC for those but it'd be neat to hook up an old Amiga or Atari. Just the ideal case for me would be as little conversion as possible before hitting the display for all devices involved.
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Re: RGBs to 15KHz VGA?

Postby maxtherabbit » 2019-9-10 @ 13:53

There were a fair number of PC-CRTs that supported composite sync just fine. It's worth trying to just passively convert the cables to a VGA connector and see if it syncs. Just make sure to connect your C-sync to the H-sync line on the VGA side
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Re: RGBs to 15KHz VGA?

Postby mothergoose729 » 2019-9-10 @ 14:06

Benedikt wrote:
derSammler wrote:VGA requires H-Sync and V-Sync, so a simple cable won't work. You need a converter. I'd use a cheap GBS 8220, which will also remove the need for a 15 KHz-capable monitor.

Alternatively, you could build a Sync Signal Separator like this one.

If you are really lucky, though, a 15kHz-capable monitor might have been built with SCART compatibility in mind and might be perfectly fine with composite sync.


A sync separator would be the best choice for maintaining signal fidelity.

You can also mod a PC Engine for c-sync.

https://assemblergames.com/threads/pc-e ... ial.58933/
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Re: RGBs to 15KHz VGA?

Postby sirnephilim » 2019-9-11 @ 02:31

mothergoose729 wrote:You can also mod a PC Engine for c-sync.

https://assemblergames.com/threads/pc-e ... ial.58933/


I'm a pretty good hand at soldering overall, I did the SNES Jr. RGB mod the old school way, no add-on chip just wires, caps and resistors. (I also modchipped a few PS2's back in the day - never again) It's why I'm confident I can fab some cables given the right spec. I just don't have the deep knowledge of the actual underpinnings of old school video. Even sold a few modded SNES systems on ebay - fair profit for a couple hours' work.

I'll add some manner of PC Engine to my collection eventually, it's just not as nostalgic to me as the Nintendo and Playstation systems. I did own a Turbo Duo at one point - I have NO idea where it went. I'm assuming mom tossed all my old gaming stuff but she won't admit to anything and that was 20 years ago... (Seriously, moms may be the greatest threat to game preservation in existence.) At any rate it's not that high priority for me, there weren't many games I cared about. Sega has higher priority for me and I never actually owned one of those except for a Dreamcast.
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Re: RGBs to 15KHz VGA?

Postby Jo22 » 2019-9-11 @ 03:02

Some DOS emulators for arcade games supported SCART video monitors (or real old cabinet screens) to be used with a VGA card/PC combo.
These cards then ran out-of-spec of the "normal" VGA modes we know, of course.
If memory serves, there used to be DOS utilities that did the job for this purpose.
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