Sega Megadrive zipper lines, fixed but not really? Now Really :)

[RockstarRunner]

I have a MD1/MCD1/32X combination, and it's connected to my TV via RGB scart.
Problem is zipper-like vertical lines in the picture, this can be seen on md, cd & 32X games.
Rest of image is sharp, clear, colourful & does not flicker.
The zipper-lines appear static on the screen and don't 'scroll' or anything like that, they can't be seen in whites, and are faint in dull colours, like light grey or something.
I've attached a few pictures to show what I mean, but they look a bit off 'cause I took them with my iPhone.
All the sega equipment and games are PAL, TV is a Sony Bravia LCD.

After doing some reading I came accross the suggestion that cutting cutting leg 6 on the cxa1145p  would somehow remove the interference, so I did this, and then tested with only the Megadrive hooked up.
It seems that cutting leg 6 on the cxa1145p was all that was needed to clear up the megadrive picture, as the zipper lines had completely gone, for testing sakes I bridged the cut leg 6 while looking at the output, and the lines came back, removing the bridge and they were gone.
So, all would be well except that when playing games through the 32X the damn zipper lines are back! 32X games aswell as regular megadrive games show the lines through the 32X.
Anybody have a suggestion if I can something similar to the 32X that I did to the MD?

[RockstarRunner]

Another bit of info, when playing Blackthorne, with the megadrive and 32x switched to 60hz, the lines are still there but are straight, like the commonly seen 'jail bar' effect.

[Midori]

If you use the 32X you feed the RGB signals from the Mega Drive into the 32X addons own CXA chip. The 32X has its own video encoder, that might be why you get the zipper lines again.

[RockstarRunner]

Thanks for the input, do you happen to know which chip that is on the 32X? Is it that one to the right of the cart slot... I forget the number

[Midori]

Nope, sorry. Never played around with a 32X :-) So I have little practical experience with it, but info should be around. Just search for it.

[RockstarRunner]

So i'm trying to find info on 315-5788, that seems to be the video mixer... can't find a damn thing that helps... no pinouts anywhere. I really dont want to start cutting legs at random.

[Tiido Priimägi]

The cable is the one that is faulty here, its not putting the TV into RGB mode, but instead its in an intermediate state, where its picking up info from the composhit line, and the jailbar madness comes from the composhit line...

For 32X just remove the crystal from the encoder circuit, there are 3 pins dealing with subcarrier generation. Alternatively you can use Composhit Sync for sync, or LM1881 to create sync from composhit signal.

[RockstarRunner]

  Thank  you so much!
> For 32X just remove the crystal from the encoder circuit, there are 3 pins dealing with subcarrier generation.
Can you give some guide what I should do for this, I don't know which pins to attack.
Thanks again!

[Link83]

Why not try using the 32X's dedicated C-Sync output on pin 5 by rewiring the DIN plug?:-
http://members.optusnet.com.au/eviltim/gamescart/gamescart.htm#mega2
Seems like a better/less destructive method that cutting chip legs and taking crystals out of consoles.

It might also be a good idea to make sure the RGB Scart cable is good quality and well shielded, and remove any unnecessary pins from the Scart plug which could possibly add interference:-
http://en.wikipedia.org/wiki/SCART#Practical_considerations

Quality differences exist in SCART cables. While a proper SCART cable uses miniature coax cables for the video signals, cheap SCART cables often use plain wires for all signals, resulting in a loss of image quality and greatly reducing the maximum cable length. A common problem is that a TV outputs a composite video signal from its internal tuner, and this is induced or cross-talked onto an incoming video signal due to inadequate or non-existent screening on a cheap SCART cable; the result is ghostly images or shimmering superimposed on the incoming signal. To non-destructively verify if a SCART cable uses coax cables, one can unscrew the strain relief at the SCART connector and fold open the plastic shell.

Using higher-quality cables such as those with ribbon cords that have properly shielded coax cables inside might help in reducing a 'ghosting' effect, but it does not always completely eliminate it due to various factors. A more permanent method is to remove pin 19 from the SCART plug that is put into the TV. Pin 19 is Video Out, and removing it prevents a signal from being broadcast by the TV into the cable in the first place, so it cannot cross-talk with the incoming signal. Cheaper SCART plugs can sometimes have the pins pushed inside the connector housing so as to remove it in a non-destructive manner (and thus allowing for its replacement in the future should the need arise by simply unscrewing the housing and pushing the pin back through its hole), though sometimes the pins are fixed in place on the inside by glue or rubber and can only be removed by forcefully twisting them off entirely. Generally though, for a standalone TV there is no need for video output on the TV end of the SCART plug, so in the majority of cases removing it completely should not be a problem

[RockstarRunner]

I had planned to try the sync as a possible alternative, but I still really want to know what can be done to the chip... Composite can go leap off a cliff for all I care.

[Link83]

I had planned to try the sync as a possible alternative, but I still really want to know what can be done to the chip... Composite can go leap off a cliff for all I care.

Sorry but that doesnt make sense? The Composite video signal could be whats causing the 'zipper lines' in RGB in the first place, especially since you said in the first post that they disappeared from the Mega Drive's RGB output when you cut CXA1145 pin 6 (Which basically disables the color subarrier for the CXA1145's Composite/S-Video output) The 32X has its own custom ROHM video encoder with its own color cubcarrier, so the Composite video output will be 'fixed' by the 32X, regardless of you cutting pin 6 on the Mega Drive's CXA1145.

If you would rather mess about with the console and cut pins/remove crystals than rewire a DIN plug, then thats fine - but i'm not sure how you expect to narrow down the cause and fix the issue if you dont approach this scientifically and test all the possible variables.

<EDIT>Perhaps you dont realise that RGB always requires a sync signal, and that RGB Scart takes the sync signal from the Composite video signal? This is why you cant just remove the Composite video signal, because there would be no sync. Thats why i'm suggesting you try using the C-Sync output instead on the Scart cables Composite video pin/wire to see if that removes the zipper lines - that should at least confirm if the Composite video signal is actually causing the zipper lines in RGB or not.

[RockstarRunner]

Can you blame me for looking for a similair solution for the 32X that worked so well on my MD? I've spent a long time trying to find a solution for this, and this is the first place that's come up with something, so for your guys help I am grateful, but the information about what the pins on the 315-5788 do has proven so elusive that I just need to know, for reference's sake if nothing more.
I will certainly try the c.sync wire change first before anything else more 'drastic', to do otherwise would be foolish... looking at my video cable though it's fully molded plugs, don't think I can rewire that sucker unless I cut it in half and do it in the middle of the cable 

[Link83]

What i'm trying to say is that using C-Sync instead of Composite video is a similar less destructive solution to cutting pin 6 on the CXA1145, they should both do almost the same thing - just in different ways.

You may find a partial pinout for the 315-5788 online, but from what I have read this is a custom video encoder chip made by ROHM for Sega, so you will be very unlikely to find a full pinout/datasheet anywhere. Besides, Tiido Priimägi already explained that removing the 315-5788's crystal oscillator would be the exact same thing as cutting pin 6 on the CXA1145.

Unless its an official Sega/manufactured RGB Scart cable then it probably doesn't use molded plugs, take a look at this page to see how to make a Mega Drive 2/32X RGB Scart cable and get an idea as to how best to open the DIN plug:-
http://www.mmmonkey.co.uk/console/sega/md2-scart.htm

[RockstarRunner]

Ok, so I tried changing the wiring so that C.Sync goes to scart pin 20, as was suggested.

Initial result testing Virtua Fighter 32X, looked good, but very quickly some colours faded to black, and the backgrounds (rendered by the MD?) where just black.

I then added a  220uF capacitor and a 75 ohm resistor inline with the C.Sync mod.

Now the colours dont fade away and the backgrounds can be seen.
Problem is though the damn lines are still there, they are much fainter after the mod, but still there.

Any further suggestions? I want the damn things gone completely.

<edit-addition>
In 60hz mode, playing Blackthorne, I couldn't see any lines at all, but it is kind of a dark game.

[Link83]

Is your Scart cable shielded/screened? and have you tried removing any unecessary pins from the Scart plug?

You could also try using an LM1881 on Composite video as Tiido Priimägi suggested, as it can often help clear up Sync issues.

Are the lines still present when using only the Mega Drive with no 32X connected? (I am guessing you have both MD1 and MD2/32X Scart cables as you mentioned testing the MD1 separately in the first post)

[RockstarRunner]

About the cable, I tested both with the same cable, using the MDto32X adapter that comes with the 32X when connecting to the md.
The picture when connected to just the md is perfect, with the cut leg as the only mod.

[Link83]

I meant have you tested it since rewiring the cable to use C-Sync instead of Composite video? Also, even if the picture is perfect with just the cut leg Mega Drive, the Scart cable could still cause of intereference if it has poor shielding.

[RockstarRunner]

Sorry it took a while for me to reply, got around to testing just the MD, and the picture looks clean, so I really cannot see how the cable can be at fault.
Tiido hasn't got back to me about how the sub-carrier is going into the 315-5788, so I can't look into that avenue yet. I have a feeling that the problem is caused in that chip as the symptoms look the same as I had with the MD, and the reason I heard for cutting leg 6 on that was that it interfered with the rgb signal in the chip (lines close together or something?), and also it's like on the Neo (which I have and fixed) that the video encoder really ruins the rgb signal when it generates the composite signal, tapping the rgb before and everything looks great... I dont think thats an option on 32X as isn't the 315-5788 doing some combining of MD & 32X video?
I don't have the parts to try that LM1881 mod, and also don't believe it would help, as the C.Sync mod didn't truly fix it either, don't want to be stuck with these shitty lines 

[RockstarRunner]

Hmm, so it's perfect on 32x now, the c sync mod did do the trick after all, I think I just had a poor solder connection on one wire. Massive thanks to Link83! And Tiido for the input.