Vertical screen rolling on some games

[technozombie]

I'm having an issue where I have vertical screen rolling on some games. It happens on the Konami logo on Rondo of Blood, the second stage of Space Harrier and when I re-enter the first castle on Mysterious Song. It is a DuoR from doujindance. I'm using a Euro scart cable into a scart to component box. My genesis and SNES don't have this problem. Any ideas? Thanks.

[pulstar]

Does this only happen on bright screens like when the Konami screen turns white?

[technozombie]

A white screen will do it for sure but it doesn't have to be. While in the 240p test suite the "white & RGB screen" test will do it every time. I also have another issue as seen in this picture.

[pulstar]

Looks like a sync issue. Try a resistor on the sync line first. Around 220ohms. If not it may need a sync stripper or even to be amped.

[technozombie]

OK, I opened up the cable and there is a resistor inside, it is soldered to pins 8 and 16.
Is that where it should be?

[pulstar]

That is to open the rgb mode and enable auto switching if you were running it on a TV. That needs to be there. Sync is pin 20 on euro scart cables. Try the resistor on there first and see if that helps.

[technozombie]

Thanks. Hmmm I wonder if my local radio shack is open.....

[technozombie]

Well the resistor did improve picture a little it seems but it is still rolling and doing the tearing thing. Here is a picture after the 220ohm resistor. The first block of the color looks better, although it may be hard to tell from the pictures.

[pulstar]

Before messing with sync strippers or amping the sync line, try and increase the resistor to around 1k ohms. If that doesn't work you'll probably have to try a sync stripper circuit or possibly amp the sync line.

[technozombie]

I already have some 1k resistors so I'll give that a try. Should there be resistors anywhere else? Doesn't the SNES usually have three?

[technozombie]

The 1k resistor made it completely unplayable.

[pulstar]

Right. That isn't great then. Are you taking the sync from Composite Video or direct from the sync on the HuC6260? If it is Composite Video you'll probably need a sync stripper circuit. Remove the resistor from the scart end and build this circuit - http://gamesx.com/wiki/doku.php?id=av:lm1881 - and hopefully that should sort the problem.


The reason most RGB cables have resistors on the RGB lines is that the signal needs to be brought down to a certain level otherwise it looks too bright. Where the PCE needs to be amped, the resistors in the Scart can be omitted to.

[technozombie]

I bought it already modded  so I don't know how it was done. I'll pop it open tomorrow and take a look.

[pulstar]

If it's using composite video as sync it could be the component box or the monitor being picky about the sync not being clean.

[technozombie]

It is doing now on my Genesis although I don't remember it doing that in the past.