Patterning on RGB on a Master System and SNES

[chinnyhill10]

Just bought an RGB cable for my Sega Master System and was disappointed that I'm getting pattering on the image like this:

My SNES also does this on RGB as does my C64 when plugged in via S-Video.

The patterning is too regular and static to be video interference. In the past I've tried larger resisters in the cable but they only make the picture dimmer, the pattern is always there.

As this is now the 3rd device where I have this happening (RGB on the SNES and SMS and S-Video on the C64) I really want to try and get it solved.

My Megadrive, Amiga, Amstrad CPC, Spectrum and Dreamcast all use the same RGB input flawlessly. My Saturn works just about satisfactorily.

As I say I don't think it's the cables because interference to an analogue video signal wouldn't be so regular, static, and well defined. My suspicion is there's something the upscaler in the TV doesn't like.

Anyone come across this before? Any ideas?

Thanks.

 

[breech]

I saw some very detailed threads about this problem on assemblergames but from memory that was after mods.

 

[chinnyhill10]

I've been reading a lot of such threads on various forums and the usual thing that crops up is blaming the cable. I don't believe it is in this case. I think it's the upscaler in the TV. The pattern is just too regular.

We have 2 Samsungs of a similar age. Both show the patterning and the worst colour for it is blue. If the screen is scrolling left or right the patterning disappears only to return when the screen is static again.

When the screen is static in Sonic, if an object moves over the blue background, the object leaves a pattern free area for a fraction of a second.

Need to try it on another TV really.

Would be interesting to know why some hardware does it and why some doesn't.

My investigations continue!

 

[roy_bates]

if it happens with more than one system i would be blaming the tv.

it cant be the cable the cable would be different for each system.

 

[chinnyhill10]

Have done some investigations this weekend. A 100 Ohm resister on the composite line of the SMS's SCART cable greatly reduces the patterning. Tried a 150 Ohm but as the TV derives the sync from the composite signal you start to see line jitter.

However it also appears to be the case there is a grounding issue somewhere.

Tried the same thing with the SNES. 950 Ohms on the composite line gives the greatest reduction in patterning. Taking it to 1K cuts the picture totally. But again there appears to be a grounding issue.

Conclusion is that both cables are a bit rubbish and need replacing. However at least I have an RGB connection on the SMS that gives a satisfactory if not perfect picture now. Before it was unusable.

The SNES is usable and better than composite but the patterning is still quite evident.

 

[breech]

You could also try a linear variable resistor (trimpot) ~200 Ohms and find a sweet spot that way.

Speculation:
If it was me I would try a test on quality impedance matched shielded cable to see if the image clears up (coax/mic etc). It could be basic crosstalk or even wifi interference. Maybe try earthed foil around the cables to block external noise.


[edit] fixed

 

[Bryce]

Have you tried turning off any "automatic enhancing" in the TV?

@breech: I think you mean a variable resistor. A varistor is a completely different component.

Bryce.

 

[breech]

Oops, thanks. I've been using them at work so got them mixed up icard

 

[chinnyhill10]

You could also try a linear variable resistor (trimpot) ~200 Ohms and find a sweet spot that way.

Speculation:
If it was me I would try a test on quality impedance matched shielded cable to see if the image clears up (coax/mic etc). It could be basic crosstalk or even wifi interference. Maybe try earthed foil around the cables to block external noise.


[edit] fixed

I think it's probably grounding.

The system is connected to the TV via a SCART splitter box. All the connections are isolated except for an audio feed which goes out to some speakers.

Unplug the speakers and the interference gets worse. I suspect the speakers are improving the grounding situation.

It's so hard to find good cables. The reputable dealers I know (e.g. Retro Computer Shack) don't sell cables for the SMS 1 or the SNES. I wonder if there are any Amibay sellers who sell cables that are properly made up to a spec that work with LCD's and not just CRT's.

---------- Post added at 12:02 ---------- Previous post was at 12:00 ----------

Have you tried turning off any "automatic enhancing" in the TV?

@breech: I think you mean a variable resistor. A varistor is a completely different component.

Bryce.

TV is in "game" mode. Said TV is also fine with my Megadrive, Dreamcast, CPC, BBC and Amiga all of which connect via RGB. My Saturn is OK but could be better.

 

[roy_bates]

have you tried the cables without the scart splitter?

directly into the tv.

after seeing this,it might not be the cables.

 

[chinnyhill10]

have you tried the cables without the scart splitter?

directly into the tv.

after seeing this,it might not be the cables.

Yes, done all of that.

 

[sir_beaker]

Pretty sure I was using my Megadrive 1 RGB cable from Retro Computer Shack on my Master System 1 base unit... unfortunately TC has my SMS1 base unit for modding so I can't test it at the moment to confirm.

 

[chinnyhill10]

have you tried the cables without the scart splitter?

directly into the tv.

after seeing this,it might not be the cables.

Yes I have tried that.

I am pretty sure it is the cables.

---------- Post added at 01:02 ---------- Previous post was at 00:59 ----------

Pretty sure I was using my Megadrive 1 RGB cable from Retro Computer Shack on my Master System 1 base unit... unfortunately TC has my SMS1 base unit for modding so I can't test it at the moment to confirm.

I would have purchased a lead from him but he didn't have any at the time.

 

[chinnyhill10]

Sorry to drag up an old thread but I have useful info.

The interference did indeed seem to be coming from the composite line where the RGB was deriving it's sync from. The larger resistance I added to the line the more the effect reduced but also the video started to become unstable.

I managed to find a company selling cables that offered sync without the composite signal being present. Cable arrived today and this is the result:

The company I used was called Retro Gaming Cables and it was their Megadrive 1 cable (mono) with composite sync that did the trick.

 

[scrappysphinx]

I have a samsung tv that does this also. I switched my cable to use the c-sync instead of composite and it greatly increased the picture quality. I've now done this for my mega drive & master system

 

[Firthy2002]

Sorry to drag up an old thread but I have useful info.

The interference did indeed seem to be coming from the composite line where the RGB was deriving it's sync from. The larger resistance I added to the line the more the effect reduced but also the video started to become unstable.

I managed to find a company selling cables that offered sync without the composite signal being present. Cable arrived today and this is the result:

The company I used was called Retro Gaming Cables and it was their Megadrive 1 cable (mono) with composite sync that did the trick.

View attachment 73151

I've got Amiga and MegaDrive 1 cables from them and they are near flawless.
I also have the same problem as you did with my SMS1, likely caused by a cheap cable, so will be buying another cable from them in the near future!

 

[chinnyhill10]

I also have the same problem as you did with my SMS1, likely caused by a cheap cable, so will be buying another cable from them in the near future!

It's not the cost of the cable. It's the way it is wired. Important distinction as there is a lot of misinformation out there. Just buying a more expensive cable won't fix it but the correct wiring (as explained above) will.