Clean sync RGB to CVBS-as-sync RGB help

[Bassa-Bassa]

Would love to read some opinions from the experts here as I don't know even where to begin or if this is an achievable project. Which circuitry exactly would be needed to make a cable/adapter for that?

I guess there are already RGB-to-CVBS video signal solutions around, but my need is RGB video signal (and SCART). Some may be already aware - Sony RGB TVs with an FE2 chassis don't display properly red color from pin 15. It does if it comes from pin 20, so clean c-sync or sync-on-luma RGB don't work well enough with these TV sets, but CVBS-as-sync RGB works flawlessly. I think this latter part isn't too well known and many people think these TVs are useless for RGB but they actually aren't, depending on the source.

I've been told that consoles often use a CXA1145 to output both, C-sync and CVBS-as-sync RGB. Is that an affordable solution? Otherwise, to use an active adapter to combine C-sync with blanking in order to fool the TV set, though I do think that the TV needs Red on pin 20, after all the tests I've done.

Any advice is welcome as I know next to nothing about electronics. But it may well be worth it as there are quite a few models with this chassis which otherwise is quite a nice one (and a late one).

[Kez]

Most consoles output CVBS through their AV out and the "standard" SCART config is with CVBS as sync. So it's just a case of getting the correct cable. Is there a particular system you're concerned about?

[Bassa-Bassa]

At least my Japanese DC isn't outputting CVBS-as-Sync RGB. I've been told that it can't do RGB like this, it's either, C-sync or CVBS video signal. Not sure if it's true, but explains my experience with two different RGB cables (and other TV sets as well). Japanese SAT and PAL PS2 work, though.

Anyway my main concern is my 15khz PC, there doesn't seem to be adapters for RGBHV (nor C-sync) to CVBS/composite-as-sync RGB. I have an (unfinished) Mister build as well. And preordered one of those Super Station One (or whatever it's called) Mister-based devices which pretty sure aren't supporting CVBS on the DIM? connector used for 15khz RGB. Most PCB control boxes wouldn't work either, my guess.

[vol.2]

I've been told that consoles often use a CXA1145 to output both, C-sync and CVBS-as-sync RGB. Is that an affordable solution? Otherwise, to use an active adapter to combine C-sync with blanking in order to fool the TV set, though I do think that the TV needs Red on pin 20, after all the tests I've done.

This project will build you an adapter that can take an RGB signal and output a composite video signal. The video IC used also features an RGB passthrough. https://github.com/UzixLS/rgb2svideo

You want to use the CXA2075M. The 1145 is an older IC and inferior in every way.

Not sure if your will be able to do it with zero electronics experience, but that's what I'd use if I wanted exactly what you are asking for.

[Kez]

At least my Japanese DC isn't outputting CVBS-as-Sync RGB. I've been told that it can't do RGB like this, it's either, C-sync or CVBS video signal. Not sure if it's true, but explains my experience with two different RGB cables (and other TV sets as well). Japanese SAT and PAL PS2 work, though.

Anyway my main concern is my 15khz PC, there doesn't seem to be adapters for RGBHV (nor C-sync) to CVBS/composite-as-sync RGB. I have an (unfinished) Mister build as well. And preordered one of those Super Station One (or whatever it's called) Mister-based devices which pretty sure aren't supporting CVBS on the DIM? connector used for 15khz RGB. Most PCB control boxes wouldn't work either, my guess.

Hmm, well I don't know anything about your CRT - it is interesting that you only get proper colours with a composite video as sync cable. The CVBS signal is more akin to a component/s-video type signal than RGB though so it doesn't just have "red" in it, certainly seems like something bizarre is going on. Makes me wonder if simply using CVBS is the only way or if there is another trick that works. There are some systems where if you load out of region games and try to use composite video, the frequency is off and you get a black and white image on composite. Would be interesting to see what the TV displays if it gets a sync signal like that with RGB.

The Dreamcast does have a CVBS pin on its output (source), so building a cable (240p/480i only - no 480p) should be totally fine.

As for your other examples, getting composite from those would be tougher. vol.2's solution above seems like it could work - you'd need to split the RGB signal into 2, attach a converter onto one of them and then mix the RGB signals from the other with the new CVBS signal.

[viletim]

Bassa-Bassa,

This TV appears to have some kind of design flaw or software bug that makes it behave this way. I think it's unlikely that it's got anything to do with the red colour information present in the composite video signal itself. What is more likely is the TV has a colour detector circuit which looks for the colour burst part of the signal. This is a sample of the colour carrier frequency that appears following a sync pulse. Its main use is to phase lock a local oscillator to demodulate the colour information. A modern TVs will look for this colour burst to automatically determine whether this is a black and white, NTSC, or PAL signal. I suspect this TV has a bug when it detects a black and white video signal (which is would if you feed composite sync or luma into a composite video input), it not only disables the colour demodulator, but also changes something that adversely affects the red video signal path.

That's my guess, anyway. If it's true then it's not really difficult to put a colour burst onto a sync signal to make it 'colour composite video' according to the TV. First of all, have you contacted the guy at the email address on the page you linked to? It mentions a hardware fix...

[Bassa-Bassa]

Thanks all for the input. Getting a C-sync to CVBS-as-sync conversor looks (surprisingly, I'd say) like uncharted territory and I'm afraid it's indeed way beyond my capabilities, so I would need to find someone to make it. CXA2075M in that case, then. It's a beginning and maybe this thread serves to find the person as well!

The Dreamcast does have a CVBS pin on its output (source), so building a cable (240p/480i only - no 480p) should be totally fine.

Well, I've been told that you can't make the DC generate CVBS and RGB at the same time. I guess it's designed like that however it manages to do it. But you never know, maybe there's a workaround to ignore that. Would need further research.

This TV appears to have some kind of design flaw or software bug that makes it behave this way. I think it's unlikely that it's got anything to do with the red colour information present in the composite video signal itself. What is more likely is the TV has a colour detector circuit which looks for the colour burst part of the signal. This is a sample of the colour carrier frequency that appears following a sync pulse. Its main use is to phase lock a local oscillator to demodulate the colour information. A modern TVs will look for this colour burst to automatically determine whether this is a black and white, NTSC, or PAL signal. I suspect this TV has a bug when it detects a black and white video signal (which is would if you feed composite sync or luma into a composite video input), it not only disables the colour demodulator, but also changes something that adversely affects the red video signal path.

That's my guess, anyway. If it's true then it's not really difficult to put a colour burst onto a sync signal to make it 'colour composite video' according to the TV.

Even though I myself haven't understood it completely, sounds like it's worth trying before anything else, thanks again. Any advice to find a specified colour burst for the matter?

First of all, have you contacted the guy at the email address on the page you linked to? It mentions a hardware fix...

I'm on it, the address is obsolete, but I think I can reach them.

[Syntax]

Bassa-Bassa,

This TV appears to have some kind of design flaw or software bug that makes it behave this way. I think it's unlikely that it's got anything to do with the red colour information present in the composite video signal itself. What is more likely is the TV has a colour detector circuit which looks for the colour burst part of the signal. This is a sample of the colour carrier frequency that appears following a sync pulse. Its main use is to phase lock a local oscillator to demodulate the colour information. A modern TVs will look for this colour burst to automatically determine whether this is a black and white, NTSC, or PAL signal. I suspect this TV has a bug when it detects a black and white video signal (which is would if you feed composite sync or luma into a composite video input), it not only disables the colour demodulator, but also changes something that adversely affects the red video signal path.

That's my guess, anyway. If it's true then it's not really difficult to put a colour burst onto a sync signal to make it 'colour composite video' according to the TV. First of all, have you contacted the guy at the email address on the page you linked to? It mentions a hardware fix...

What is the easiest and cleanest method to do this? There are a few LG sets that require it when RGB modding else the color demodulator is disabled.

[Bassa-Bassa]

Hopefully you don't mind a bump. Would really love to find a solution for the issue which may also help others and I'm afraid I don't even know what a colour burst (onto a sync signal) is to start searching.

[vol.2]

Hopefully you don't mind a bump. Would really love to find a solution for the issue which may also help others and I'm afraid I don't even know what a colour burst (onto a sync signal) is to start searching.

Color burst is the signal used by the TV manufacturers to add color to a black and white TV picture. When they invented color TV, they wanted to make sure the signal they used was fully compatible with all the existing black and white TVs, so instead of starting from scratch, they decided to keep the black and white signal, and just add on another "color burst" signal that is added onto the black and white. The resulting video signal is referred to as "composite video" because it's a composite of the black and white and the color information. In the case of composite video, it is the black and white portion that contains the sync information

Some RGB systems can use, or require the use of "clean sync," which means that the sync contains no color information. It seems that your situation is the opposite, and the TV requires composite video as sync, or that's my interpretation of your post.

I'm not sure if there are any really good off-the-shelf solutions to do this. It's a fairly trivial thing to do if you have some skills in building video electronics. The RGB to S-Video and Composite adapter I linked for you will take an RGBS signal and spit out RGB, Composite and s-video. That will do it. You might be able to find someone making them, or you could try uploading the PCBs to a small service house like PCBWay and having them build one for you, but you might need to make some basic changes to the design in order to make sure that your video options are enabled.

As far as off-the-shelf solutions go, I'm not sure how signal path delay would factor into it. If you tried to feed the TV RGB from your source, and then also processed it to spit out composite video with a cheap processor from Amazon, or even many of the more expensive devices, there could be too much delay in the sync information for it to work. Then again, idk there could be something easy out there you could use that I don't know about, or the delay might not have such an impact. One of the more experienced people here will have to chime in.

[Bassa-Bassa]

Very informative, thanks. So viletim's suggestion involves a custom PCB as well? I was hoping some simple circuit for that colour burst needed would do...

[vol.2]

Very informative, thanks. So viletim's suggestion involves a custom PCB as well?

Tim didn't offer a specific suggestion, just that you could...

...put a colour burst onto a sync signal to make it 'colour composite video' according to the TV.

Meaning that a solution is possible and somewhat trivial.

and that you should contact...

...the guy at the email address on the page you linked to? It mentions a hardware fix...

Meaning that your original link with info on this problem mentions a solution, and did you follow up on that initial suggestion and you should do so if you have not.

Syntax then followed-up by asking Tim:

What is the easiest and cleanest method to do this?

And that's where it stands.

I was hoping some simple circuit for that colour burst needed would do...

Simple, I suppose, is in the eye of the beholder. As I said before, the only issue I immediately see with a cheap and easy off-the-shelf solution is that it may introduce some unacceptable amount of lag which could cause the sync to be out of time with the color information or simply just be laggy and bad to play. I'm not a real "lag expert" like some of the other folks here, so I can't say.

This is of course assuming that you are working with a source that does not already output a composite video signal in addition to RGB output. If your source does output both at the same time, the easiest solution would be to just build and adapter that puts the composite video on the sync pin of your SCART connector. You could do that by building a female to male SCART cable, but hanging the connection for the sync pin out of the side and attaching that to a female RCA jack. SCART pinout: https://crtdatabase.com/modding/wiring- ... -connector

[Bassa-Bassa]

Very informative, thanks. So viletim's suggestion involves a custom PCB as well?

Tim didn't offer a specific suggestion, just that you could...

...put a colour burst onto a sync signal to make it 'colour composite video' according to the TV.

Meaning that a solution is possible and somewhat trivial.

and that you should contact...

...the guy at the email address on the page you linked to? It mentions a hardware fix...

Meaning that your original link with info on this problem mentions a solution, and did you follow up on that initial suggestion and you should do so if you have not.

Syntax then followed-up by asking Tim:

What is the easiest and cleanest method to do this?

And that's where it stands.

Hence the thread bump. It's just I wasn't sure any colour burst addition as per viletim's suggestion would involve custom PCB no matter what after reading your following reply, so I wanted to make sure in the meantime, given that any custom PCB requirement would likely put an end to my plans.

As for the page I linked to, I did mail them (at another address as the one posted there doesn't work). The guy invited me to just make the question on his private forums like if he didn't know about the matter anymore or he's just not the author. And I'd hardly believe those have more knowledgeable people than this place.

This is of course assuming that you are working with a source that does not already output a composite video signal in addition to RGB output. If your source does output both at the same time, the easiest solution would be to just build and adapter that puts the composite video on the sync pin of your SCART connector. You could do that by building a female to male SCART cable, but hanging the connection for the sync pin out of the side and attaching that to a female RCA jack. SCART pinout: https://crtdatabase.com/modding/wiring- ... -connector

Thanks but nope, the issue is with RGBHV/clean sync/sync-on-luma-only sources - old ATI graphics card and Mister (the forthcoming Super Station One, actually, but I guess it's a safe bet that it won't output CVBS through its RGB connections). Still unsure about the Dreamcast, though, as I've got contradictory answers.

[vol.2]

Thanks but nope, the issue is with RGBHV/clean sync/sync-on-luma-only sources - old ATI graphics card and Mister (the forthcoming Super Station One, actually, but I guess it's a safe bet that it won't output CVBS through its RGB connections). Still unsure about the Dreamcast, though, as I've got contradictory answers.

If you are willing to just throw money at the problem to make it go away, you might be able to get this guy to make you an RGB to composite adapter with an RGB passthrough (which is the exact project I linked to you on GitHub). He is no longer offering them, but you could try asking him to make one for you and see what he says. https://www.tindie.com/products/low_bud ... converter/#

His adapter uses a different encoding IC than I recommended, but it's one that is still available. I just used NOS Sony ICs for my own projects.

[Syntax]

https://www.ebay.com.au/itm/395643916531?

You could plug your systems thru the scart in, and steal the RGB from the RCA RGB in and couple that with the composite out.

Its a bunch of odd cables, but no soldering and a fairly affordable unit.

Failing that, this has a proper buffered RGB passthru and everything you need.

https://www.jrok.com/hardware/RGBv4/index.html

https://jrok.com/hardware/RGB.html

[Bassa-Bassa]

Thank you both for the links, guys. Will mail them. -If anyone reading this knows of similar solutions within the EU, please, let me know!-

[viletim]

What is the easiest and cleanest method to do this? There are a few LG sets that require it when RGB modding else the color demodulator is disabled.

Isn't this a good thing when you have an RGB input? Or is there another TV that behaves like Bassa-Bassa's?

The easiest way to put the colour burst on a sync signal to make 'colour sync' is to use an LM1881 to get the sync signal in the fist place and a video encoder chip connected to a 3.58Mhz oscillator to make it into colour video. Instead of the video encoder chip it's possible to gate the output of the oscillator with the BP output of the LM1881. You would need some additional logic gates/one-shots to make sure it's off for serration pulses and vertical sync and that makes it more complicated. Video encoder chips are easy enough to get in small quantities for now. The circuit can accept KA2198BD or BH7236AF for U8. Maybe others with some modification, but these are the two I'm familiar with. There is no video input to the video encoder as composite video works better as sync if there is no luma or chroma present.



Bassa-Bassa,
For an off the shelf solution buy a Sync Strike to do the sync separation. The SCART socket is the input and the terminal block is the output. Cut the end off a SCART cable and wire it the signals on the terminal block. The used to a few different composite video encoder boards on the market, but they are rare now. This Arcade RGB CGA to TV and Video Composite Converting board is the only one I could find. It should do the job. Just connect the TTL sync from the Sync Strike the video encoder's sync input and leave the RGB inputs unconnected. The composite out goes to the output SCART.

[Bassa-Bassa]

Thanks for that detailed post, viletim. Unfortunately, that Aliexpress seller won't ship his encoder to Europe. How did you like Syntax' sample (or even vol.2's, though that's not available currently)?



Is it a problem that it takes RGBS instead RGBHV? Source actually outputs the latter as it's an ATI card for PC, but turning it into RGBS is trivial. Not sure if that (VGA video hardware) normally implies TTL, I think it does?

[vol.2]

I can't answer for Tim, but I can tell you this.

Is it a problem that it takes RGBS instead RGBHV? Not sure if that (VGA video hardware) normally implies TTL, I think it does?

That's what the sync strike would be for. The LM1881 can take the HV and output clean sync.

Not sure if that (VGA video hardware) normally implies TTL, I think it does?

No it does not. TTL is mostly confined to specific 8-bit microcomputers and industrial equipment. VGA is never TTL, it has an analog video output stage.

[jd213]

Thanks for that detailed post, viletim. Unfortunately, that Aliexpress seller won't ship his encoder to Europe. How did you like Syntax' sample (or even vol.2's, though that's not available currently)?

Timexpress sells this converter on their site in addition to Aliexpress, they might ship it to Europe:
https://timeharvest.net/products/scart- ... g-pcb-1634

I believe another fan-developed RGB to S-Video/composite adapter was briefly mentioned on one of RetroRGB's weekly videos (apparently it's been repeatedly pushed back though), so that might be another option sometime in the future.

[Syntax]

Combine the sync with diodes and hope for the best I say!

[Bassa-Bassa]

Combine the sync with diodes and hope for the best I say!

Is it a problem that it takes RGBS instead RGBHV? Not sure if that (VGA video hardware) normally implies TTL, I think it does?

That's what the sync strike would be for. The LM1881 can take the HV and output clean sync.

viletim said "buy a Sync Strike to do the sync separation", so I understand the device he's suggesting (and that isn't displaying on my end for the stupìd Aliexpress policies) takes RGBHV (and he thought my source was RGBS)?

Not sure if that (VGA video hardware) normally implies TTL, I think it does?

No it does not. TTL is mostly confined to specific 8-bit microcomputers and industrial equipment. VGA is never TTL, it has an analog video output stage.

Thanks. That means same electrical levels as consumer TV sets? I'd swear I read otherwise.

Thanks for that detailed post, viletim. Unfortunately, that Aliexpress seller won't ship his encoder to Europe. How did you like Syntax' sample (or even vol.2's, though that's not available currently)?

Timexpress sells this converter on their site in addition to Aliexpress, they might ship it to Europe:
https://timeharvest.net/products/scart- ... g-pcb-1634

Thanks for that as well. Description is terribly confusing, I'm afraid. I messaged them in order to confirm if it does RGB passthrough.

In the end, aren't I just outputting sync-on-CVBS RGB with any of these adapters/encoders if they work as we expect? I feel like if viletim's colour burst idea is somehow lost or am I missing something? Is it that the colour burst signal is always there no matter what if it's CVBS (that's what vol.2 explained?)? On the other hand, in case I wasn't clear enough, I'm pretty sure the only colour really affected by this behaviour is red.

[vol.2]

viletim said "buy a Sync Strike to do the sync separation", so I understand the device he's suggesting (and that isn't displaying on my end for the stupìd Aliexpress policies) takes RGBHV (and he thought my source was RGBS)?

The Sync Strike has the ability to take either RGBS with the S being C sync or composite video, or RGBHV from the screw terminals on the side. It labels them as RGB C and V, and the V goes unused unless you are using HV sync, in which case you put the H sync information into the C terminal. The main input of the Sync Strike is a normal SCART connector and it will just take normal video info that is typically present on a SCART connector, which you can easily look up.

So it can do either. The LM1881 will take either and spits out clean sync.

Thanks. That means same electrical levels as consumer TV sets? I'd swear I read otherwise.

It is essentially the same, yes. The main difference is that TTL is digital, meaning each signal is "on" or "off" for each pixel, and the only change for a shade you get is with the intensity bit, which just gives you light or dark of each color. VGA is analog, so it gives you varying signal strength per color to effectively give you a continuously changing amount of shades, up to the ability and bandwidth limitations of the device you are using (video system).

[Syntax]

If you can find an Extron unit cheap grab one, they will sort all your sync combining or separating issues, except cleaning sync off green.

https://www.ebay.com.au/itm/186768361094?

[Bassa-Bassa]

Thanks again. I'm not concerned about sync combination as I currently have a RGBHV-to-clean sync SCART cable but if the chain indeed ends up being too long, I'm not sure this is going to be worth it.

https://www.jrok.com/hardware/RGBv4/index.html

https://jrok.com/hardware/RGB.html

This one seems to be a thing of the past, I'm afraid. Even the mail account isn't working.

Still waiting for an answer from Time Harvest/Time Express and others. Not much faith left at this point.

[Syntax]

Tim pointed out that you do not need to feed RGB into the circuit, just the sync.
This is a big win for me, and should make your chain much shorter.

If your happy to make your own custom cable then there are plenty of options where you can insert only sync/ground and have the convertor add the colorburst signal/subcarrier.
This cheap ebay unit will combine the HV sync into composite sync as a bonus. I cant say if it will work for 240p content
(I do randomly own one tho)
https://www.ebay.com.au/itm/186261979744

[Bassa-Bassa]

This one, isn't it? Let me know if I get it right - assuming your cheap ebay unit takes 15khz RGBHV, I should input there a Dsub cable with only syncs and ground wired and then use the device's RCA output to get the syncs on CVBS. I should wire that cable to a (male) Scart's pin 19.

R-G-B go directly from the source to pins 15, 11 and 7, and also blanking and status signals to pins 8, 16 (and 3 and 1 if I want audio). And the rest?

Even if the chain is not long, I can't picture it being an easy to order, "clean and tidy" solution whatsoever?