If anyone examined my previous post about purple/pink lines appearing at the top of my VHS-to-MPEG conversions, I believe I have found the answer.
BACKGROUND: I am using the ATI TV Wonder Pro card to capture 10-14 year old home VHS movies to DVD. Most of time the picture looks lovely, but at times the upper 1/3 of the screen will turn purple, or there will be general color instability. On a VCR, however, these pictures look fine.
At first I thought my RF Attenuator would fix it, but it didn't. Then I tried getting a S-Video converter and cable. No good. I tried uninstalling my ATI driver and re-installing; taking the card out and putting it back in in case it had gotten a static electric charge. Still nothing.
After 20 hours of this, I found this post about Macrovision protection, old VHS tapes and ATI capture cards. ATI cards can mistake weak or unstable video signals, like old VHS tapes provide, for Macrovision, and will behave as though Macrovision is present.
This makes sense because even when I look at blank sections of the tape, where there is nothing but a blue screen, the picture will flip out, also. So...I guess I'll just deal with it. Unless somebody has an idea.