Anyone here has an original SEGA md/sms rgb-scart cable?

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keropi

keropi

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Hiya!

I found a pic of an original sega megadrive rgb scart lead:

29gmmpk.jpg


as you can see it's more complex than the leads you can get from eBay ... I was wondering if anyone here has one like that so we can see what kind of amplification Sega used...
 
There looks to be some video conversion going on in that box. MD has rgb natively and should not need all that circuitry :what:

Is there a better picture so we can see what chip that is?
 
Probably amplication.

Also possibly some filtering.... its known there are jailbars on the MD1 when using RGB
 
I don't have a better pic, I have asked the eBay seller if he can make some but I won't hold my breath ...
I was thinking at the same lines as Bad_Ad84 for this... maybe we get lucky and someone here has this cable
 
@Keropi-san

Thats massively over-engineered
 
LOL yeah
a local friend told me that it might not be so special after all, just an rgb-amp so that old tv's could display a picture without probs...
 
I would also hazzard a guess that its amplifying and filtering the audio -

thats one of those "build it - just in case" ... a scope-creep designed board...

"Oh we should have this.... and that... oh this is clearly needed....."
 
Afaik those jailbars only crop up on some lcd screens when the cable is resistorless. Weird to overcomplicate it like that, but maybe there's a good explanation somewhere out there :)


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I get the bars with 3 cables that have resistors... I blame the technological gap, I assume stuff that gets ignored in crt screens are amplified in the dsp of an lcd panel...
 
These bars I beleive are a composite video fault my friend -

This would explain why theres a little more hardware in the box as its is sync straining the H and V from the composit video and cleaning them up)

I suspect that the Comp Video signal is comming in too loud - as such its being distorted - an educated guess - try a CBVS ( inline ) resistor of 15 / 20 ohms see if that clears up the problem with your screen
 
AFAIR Z, some folks in assembler forum did modify their consoles to get a pure CSYNC signal but that did not help all of them...
I posted there because of my recent sms2 rgb mod, the bars are much more stronger than the md ones...
 
thats the problem my friend,

the Composite Sync not the video carrier part.

The CSync is too powerfull (loud) for the TV set and is causing this jailbar effect to appear in the image - clearly some monkey tech deicded to just tie the H and V together without any signal reduction / filtering - and then slaped on the Video information.

You can try and reduce the input level (i.e. a small inline resistor) the TV set might be able to adjust from there, however a better method would be to strain the horizontal / vertical sync's from CSYNC / CBVS and then apply them properly at the correct voltages - infact - apply them directly to the scart as H and V (keeping the volts close but just under 1vpp)
 
Would be very interesting to see if that cable would solve the stripes issue.


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The bars move to a different colour when rewiring the amp chip. I don't think it's that simple. Zetr0 there is a long thread about this on assembler.

Sent from my iPhone using Tapatalk. Please excuse any crazy auto corrects or lack of detail (links to info sources)
 
The Megadrive/Genesis has a TTL level CSYNC signal, the same as the Amiga. I referred to these schematics, http://cgfm2.emuviews.com/gen.php.

As it has the same TTL CSYNC as the Amiga, the same SCART fix should work, add a 220-330 Ohm resistor, in series with the Composite SYNC signal to the SCART lead.

Ian
 
But even using composite video does it. Also, jail bars in the blue move to a different colour if you switch the inputs on the cxa.

As I said, long thread with lots of testing on assemblergames and a fix that is supposed to work. Apparently noise due to a signal near the rgb traces. Never tried it as don't really use the md


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I have read the same long thread as Bad_Ad84 , ppl did all sorts of things from resistors/caps/transistors, even getting the csync directly from VDP and even stopping it from reaching the rgb encoder... for some it kinda worked for some it made no difference
 
Just lifting a leg fixed it for most I think. Not messing with anything else


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Composite leg?


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IIRC it was the leg that carried the signal from the VDP to the encoder...
 
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