Dotted lines - bad burn or bad DC?
 

Silly question of the day:

My Dreamcast occasionally displays faint vertical lines when displaying certain graphic modes. Up until now, the most obvious offender has been Soul Calibur -- not all, but some of the stages produce these dotted lines in the background. They're dim enough that they're not a big problem, but they've been there since date-of-purchase (which was date-of-US-release). Most games (including some FMV-heavy ones) display with no problems or lines at all.

I recently obtained an image of Evil Dead; it burned successfully, but it was by far the worst offender I've ever seen in this respect. It displays several lines of big green dots (not the small, semitransparent dots some other games displayed), which stand out during gameplay and are quite an eyesore.

What are the odds that it's a problem with my Dreamcast's GD-ROM drive, or that I simply have a semi-corrupted image, or both?

Sounds suspiciously like the graphics chip in your DC is going out or has been damaged somehow.

Does this happen only after it's been playing for some time? The Dreamcast has a big metal plate that touches two chips on the mainboard, one of which I believe is the CPU and the other most likely the video chip. The plate is a heat-sink to draw away the heat from the chips. Unfortunately, the fan in the Dreamcast isn't sufficient to draw enough air across the heatsink, and sometimes the heatsink may not even touch the chips firmly enough for it to do any good. If you're not into tearing apart your Dreamcast (I've done it, but I wouldn't recommend it unless you're very mechanically and electronicly inclined), I'd suggest doing what I've done to prevent Dreamcast lockups (due to overheating):

Turn the Dreamcast over on its side (the fan port should be UP), and place a small desk fan next to the Dreamcast, where it blows on the bottom of the console. This has kept down the internal heat on my Dreamcast enough so I can continue to play, even though my machine tends to overheat and lock up. Maybe it will keep down the graphics problems you're talking about too.

Right now, it's not happening after extended play sessions -- or, at least, it's not worse after playing for a while (suggesting overheating). I haven't had any lockups, either. The problem is picky about where it'll show up; it's only certain games, at certain times in those games. (For example, many stages in Soul Calibur are completely glitch-free, and I see no scratches or marks on my disc.) Of all my games, Evil Dead is the only one with a major problem -- and, quite frankly, it's a sufficiently terrible game that I'm not weeping over the loss. ;)

In particular, Evil Dead is the only game where the lines of dots are bright green. They've been almost clear and hard to notice when appearing in other games. It could be that Evil Dead uses a graphics mode or resolution that's unusual. Even in that game, some of the screens in the FMV are clear, but they always come back in the title screen and gameplay.

I'm not a mechanical type, so I suppose I'll see if it gets worse and grab a $69.99 used DC from my local Electronics Boutique if it does.