Possible (cheap) solution for problems with RGB Scart-to-LCD/LED TV

[emuola]

I've been tinkering with my retro computer "collection" for some time now... I want all my computers to be "ready to play" with no cable hooking/moving etc. So I've got a good quality active scart switch and rgb scart cables for all the computers (excluding the trusty old C64, which only outputs Y/C or composite). The switch is then hooked up to a led tv via scart (rgb).


The cables are cheap and it*should* be very easy to get a good quality picture from every computer in my collection. But for some reason(s) that have been discussed for a long time on various (retro)computer forums, some computers are not compatible with some modern televisions. In my collection the problematic ones are the 6128Plus and Spectrum +2. The image is wobbling/shaking -> drives me crazy For example Amiga 1200/MSX2/TurboDuo etc work just fine.


Finally I managed to get an easy/cheap solution for this. I'm no electrician (as some already probably know but I'm really happy with the outcome. Here's what I did:


Get a SyncStrike from arcadeforge.de: Sync Strike - ArcadeForge


Use either the HD15 or just the plain screw terminals (I did) and hook the SyncStrike to the scart the following way:


Sync Strike                                                                 Scart


R,G,B                                                                            R,G,B
V (vertical sync 5v -> couple of 100 Ohm resistors)     Pin 16 (the blanking, under 3v -> RGB mode)
C (composite sync 1v)                                                 Pin 20
GND                                                                             Pin18 and also 4,5,9,13,17


So, the whole process is like this:


Computer with a rgb scart cable -> Scart switch -> Sync Strike -> Television


The results are amazing! The formerly problematic computers now have a really, really good picture on my Samsung led tv.  The image quality is much, much better than for example with the GBS8200 cga/ega to vga scaler. The image is sharp and crisp with no artifacts! Rock \m/


This might me old news, but I thought I post here anyway.    I *might* post some pictures later

[Munchausen]

From the web page, I don't understand what this device actually does? It generates a new sync signal for you? 


I haven't had any problems with the quality of the image from my 6128 through scart, it looks amazing! Composite converter also works great. VGA is sometimes a bit wobbly, but not enough to bother me much, and I think this is due to me needing to resolder some stuff.

But great that it can fix these problems for you and others that might need it!

[emuola]

From the web page, I don't understand what this device actually does? It generates a new sync signal for you? 


I haven't had any problems with the quality of the image from my 6128 through scart, it looks amazing! Composite converter also works great. VGA is sometimes a bit wobbly, but not enough to bother me much, and I think this is due to me needing to resolder some stuff.

But great that it can fix these problems for you and others that might need it!

Yes, the Sync Strike is a sync stripper/cleaner. I'm no expert here, but I'd say most of the problems with retro computers and modern tv:s is the level of the sync -> some tv:s are more picky than others. With Sync Strike it is possible to have a proper sync for the pickier tv:s  


Note!


Of course the problem could also be that both my 6128Plus and Spectrum +2 are somehow "fading" (cap replacement needed?) and that's why I have had those problems. Howeevr with a crt tv both computers work great without any additional hw.


I guess Bryce will prove me wrong any minute

[Bryce]

I guess Bryce will prove me wrong any minute

No, all correct information as far as I can see. The Sync stripper removes the sync pulse on the original signal and replaces it with a proper sync signal (ie: correct voltage level and stable frequency). The problem with some setups is that old computers didn't have a nice standardised video signal generator. Most of them just cobbled a few discrete parts together to get an output. The Classic CPC gives a very nice signal because the 6845 is a real video generator, but others wren't so good, so you either have a sync signal that isn't high enough or the frequency isn't exactly what it should be. Some TVs won't have a problem with this, on other TVs you'll either get a flickering picture or no picture at all. This device solves that problem for you.

Bryce.

[emuola]

No, all correct information as far as I can see. The Sync stripper removes the sync pulse on the original signal and replaces it with a proper sync signal (ie: correct voltage level and stable frequency). The problem with some setups is that old computers didn't have a nice standardised video signal generator. Most of them just cobbled a few discrete parts together to get an output. The Classic CPC gives a very nice signal because the 6845 is a real video generator, but others wren't so good, so you either have a sync signal that isn't high enough or the frequency isn't exactly what it should be. Some TVs won't have a problem with this, on other TVs you'll either get a flickering picture or no picture at all. This device solves that problem for you.

Bryce.

Thanks Bryce I had real trouble with my 6128Plus and 2 different "modern tvs", namely an older Sony Bravia and a brand new Samsung. Both had a wobbly picture. With the Sync Strike everything works ok Strangely none of the tested crt tv:s (at least 6 different make/model) did not have any problems.

[Bryce]

Whether it's a flat screen or LCD/Plasma isn't what's important. What is important is how the TV is dealing with the SCART inputs. If they have purely analogue circuitry handling the sync, then you'll have no problems, but TVs that digitally sample the sync signal may have problems depending on how "forgiving" they are to signals that aren't 100% to the specifications.

Bryce.

[The Last Bandit]

Those SYNC strippers/cleaners are just a simple LM1881 circuit and typically cost a few euro to build on a DIY level.


There main purpose is to strip the sync signals out of a Composite Video signal which can cause a lot of problems for monitors that expect a clean sync - this is more typical of consoles. These strippers still output a composite sync along with a vertical sync though rather than unique horizontal & vertical sync pulses.


They add also a minor delay to the sync signal resulting in the picture shifted left although this is usually tiny and not noticeable compared to the shifting caused by the TV itself in decoding the sync from the composite video input. 


Modern TVs are particularly bad with interpreting non standard sync signals, I build arcade superguns and the sync of out some arcade boards will not lock on some modern TV's but will work perfectly on an old CRT.


Its still makes be cringe when someone tries to display 384x222 game on a 50" 1080p screen.
 

[Bryce]

Guilty: My NeoGeo is connected to a 50in Plasma TV (Via S-Video)

Bryce.

[The Last Bandit]

OMG.. Not even the decency to use RGB   

[TotO]

Those SYNC strippers/cleaners are just a simple LM1881 circuit and typically cost a few euro to build on a DIY level.

Absolutly.
I done this many times on my superguns or arcade systems.

[Bryce]

OMG.. Not even the decency to use RGB 

My TV only has HDMI and S-Video on the front panel. The SCART at the back isn't connected at all.

Bryce.

[redbox]

Those SYNC strippers/cleaners are just a simple LM1881 circuit and typically cost a few euro to build on a DIY level.

Any pointers to such a project?

Would be nice to have a good cheap CPC -> SCART -> Stripper -> TV solution

[The Last Bandit]

Mmonkey has a handy guide on building one.


Composite Sync Stripper LM1881 : mmmonkey

[redbox]

Mmonkey has a handy guide on building one.

That's cool - thanks.

It looks like a soldering project that even I can't get wrong!

[Lenwë]

The image is wobbling/shaking -> drives me crazy For example Amiga 1200/MSX2/TurboDuo etc work just fine.

What kind of wobbling/shaking ? Do you have pictures or videos ?


Is it the same glitch that I have with my Master System ?

If so, I'll try to attach a sync stripper inside the RGB adapter box.


(I know it's a very old topic but I'm struggling to find a solution for this)

[Bryce]

Your video is a good example of a typical sync problem. I can't garantee that a sync stripper will solve the problem, but it's definitely worth a try.

Bryce.

[keropi]

Master System and Megadrive 1 (at least the PAL variants) have a weird SYNC signal that is supposed to go through some ICs as per the original French RGB cable that has a pcb box in the middle.


What you can do and fix that issue once and for all is this: http://www.mmmonkey.co.uk/console/sega/md-sync.htm
Basically you cut off the sync signal from the mobo and patch in it's place a signal directly from the rgb encoder via 75ohms+220uf cap . This will fix the issue and improve compatibility with LCD sets.


found viletim's post explaining the sms1/md1 stock sync signal deal: http://shmups.system11.org/viewtopic.php?p=1123571#p1123571

[Lenwë]

What you can do and fix that issue once and for all is this: http://www.mmmonkey.co.uk/console/sega/md-sync.htm
Basically you cut off the sync signal from the mobo and patch in it's place a signal directly from the rgb encoder via 75ohms+220uf cap . This will fix the issue and improve compatibility with LCD sets.

It's a french console, it has no video encoder at all, no composite out, it uses C-sync + RGB only. This was designed this way as a workaround to the SECAM video norm which was specific to France. It was easier for SEGA to wire the CRT directly to the video chip via the SCART connector than using a SECAM video encoder since most french TVs in the 80's didn't even support PAL.

This design has the advantage to provide an almost perfect image quality.

Master System and Megadrive 1 (at least the PAL variants) have a weird SYNC signal that is supposed to go through some ICs as per the original French RGB cable that has a pcb box in the middle.

Exactly, I have this box too, the Sega 3085 "RGB adapter". It does nothing but amplifying the RGB and C-sync signals. It also provides a "switch" signal to the SCART port to automatically switch the TV to the correct input when you power on the console.





However the C-Sync circuit (4th diagram above) is a bit more complicated than the "75ohms + 220uf" RC circuit. The first thing I'll try is replacing it with the RC circuit.


If it still doesn't work, I'll try to attach a LM1881 in the RGB box on the Csync output (the box is already powered with 5v) to have a clean CSync signal like the OP did.

[Bryce]

Do you have a scope that you could measure the sync signal with? I suspect that you could correct the sync problem by tweaking the values of R22 and R23 in the 3085.

Bryce.

[Lenwë]

Do you have a scope that you could measure the sync signal with?

Not yet but I will get one this weekend.

[keropi]

ah, this is a completely different issue then, it does not apply to your French console. If you find the solution do post it 

[Lenwë]

So I tried linking the sync output to the sync input with the RC circuit, it changed nothing.
The sync strike circuit didn't solve the problem either.


The problem is definitely my TV. I forgot to mention that I modded my console to run in 60 Hz (instead of 50 Hz). This dramatically improved the situation, there is still some flickering (maybe 5% of the frames are bad, the rest are OK) but it's playable .


However the image is randomly cropped and sometimes the flickering is more important. It changes when I turn the console off and on.


I also tried to turn my console on before the TV but it changes nothing.


Now I'll try to get the components to build the missing video encoder in the console and just add a S-Video or composite output.

[Bryce]

The exact voltage levels, frequency and rise/fall times of the sync signal would be very useful to solve the issue. Can you measure these when you get that scope?

Bryce.

[Lenwë]

The frequencies seem to be OK and stable. I have 60Hz and 15 KHz and they're stable.

EDIT: I have to do my measurements of the voltage again, the scope was not properly adjusted.

I also bought a Megadrive on Ebay. It has the video encoder but it is not used since it is connected to the TV with my Master System's RGB SCART cable so it's also using C-SYNC and it's working perfectly fine, in PAL 50Hz and NTSC 60Hz.

I'll check the signal from the Megadrive as well and make a comparison but I think the problem is really the SMS doesn't provide a conventional PAL/NTSC resolution and my TV has problems with it.

I think I'll buy a VGA upscaler so that I will be able to attach a scanline generator to it and have great picture quality.

[Bryce]

Voltage is between -0.64v and +0.05v

Is that the Vpp of the csync signal?? That would explain why the TV can't sync to it, it's not nearly high enough for most TVs.

Bryce.