Issues with sync on Dreamcast RGB SCART

[Inkvisitor]

I use the original "Sega Dreamcast RGB SCART cable" hooked up to my TV and the picture constantly "rolls". The Dreamcast is a US unit (powered by stepdown converter) and the TV is european with support for RGB SCART on AV1.

I have taken some photos of the problem i describe:




As you can see the colors are right but there is some kind of sync issue

The unit works in composite or when connected to a VGA box.
Why isn't RGB working on my TV?

[Hojo_Norem]

On some TVs this can happen when there is no sync for the picture when RGB is active.  I can't speak for the US model DC but on the UK model when RGB is activated the composite output from the console is disabled completely so the sync has to come from the Y/Luma output line, or this it what I had to do when I hacked my own RGB cable together.  But that was nearly 6 years ago and my memory isn't the best.

It might be worth just checking pin 20 on the scart end to see if its been pushed into the plug as this would also cause the problem you describe.

[Inkvisitor]

According to this page http://members.optushome.com.au/eviltim/gamescart/gamescart.htm#dcast composite video is on pin 13 followed by the RGB pins. pin 10 is composite sync. My cable has SCART pin 20 connected to DC A/V pin 10. Would the cable have worked if it was connected on pin 13 instead ?

The reason i can't try it out myself is that the unused pins are missing from the connector and there isn't a wire for each pin.

[Hojo_Norem]

According to this page http://members.optushome.com.au/eviltim/gamescart/gamescart.htm#dcast composite video is on pin 13 followed by the RGB pins. pin 10 is composite sync. My cable has SCART pin 20 connected to DC A/V pin 10. Would the cable have worked if it was connected on pin 13 instead ?

The reason i can't try it out myself is that the unused pins are missing from the connector and there isn't a wire for each pin.

Since it's been so long I've decided to check my homemade cable.  My cable uses pin 10 aswell and works fine.  Have you tried you machine on another tv?  what brand of tv are you using? (scraping the bottom of the barrel here...)

[viletim]

There are a few things it could be...

1) Sometimes composite sync outputs can't drive a composite video input well enough to get a sync signal through.

2) If the SCART video control lines arn't connected properly (pins 8 and 16), and it's quite likely, then it's possible that the TV will enter a mode where the video (RGB) is enabled, but the sync isn't. Try going through all A/V modes on your TV.

3) 50/60 Hz incompaibility? (not very likey unless your TV is really old)