Flickering on PAL Dreamcast in 60hz

[Mangaman]

Hi all, I started this topic in the RGB forum (here), but figured this might be a more suitable spot since its talking about repairing my DC!

I have a launch-day PAL Dreamcast, so maybe it was a problem with early machines (I've seen it on my brother-in-law's PAL DC as well, and I'm pretty sure his is a launch machine, even though he bought it second-hand, but a friend of mine had a later-model PAL DC and had no problem). Anywho, in 50hz there isn't a problem, but it you set a game to 60hz (or if it boots in 60hz by default like a lot of import games), there is a constant flickering at the very top of the screen. The picture doesn't roll or anything, it just flickers in different colours - I remember that if it's a white screen, it flickers dark blue, grey and black in no discernable pattern; definitely looks like something's messing with the signal. It goes the entire horizontal length of the screen and is only a few cm long if measured vertically, but its annoying as hell. I've tried it in s-video and composite and it happens regardless. In VGA there isn't a problem though.

The only thing I haven't done is bridge R422 which changes the colour signal from PAL to NTSC (does nothing to the refresh rate), so I'm thinking it might be worth a shot to see if that fixes it up when I push it to 60hz.

As an aside, my display is fine with all the machines I've thrown at it (NTSC 3.something/4.43, PAL, PAL60, etc), so I know it's only a Dreamcast problem. I've also tried it on a couple of displays and the problem has occured on each one. The only time there hasn't been a problem is when I hook it up via VGA - no problems there.

Anywho, any thoughts on this?

-Mangaman-