Hi SuperTurbo,
I bought an Indivision sd/ff from Amigakit this past February for a 4000 I got off ebay in January. When I first hooked it up the screen was extremely jittery, so I adjusted the potentiometer slightly and the screen immediately went black. No amount of adjusting made any difference at that point, so I thought the unit was faulty.
I kept trying to adjust the potentiometer in hopes of bringing back the picture, but no amount of adjustment seemed to make any difference. In the process I was leaving the Amiga on for longer periods of time (30 minutes or more), and eventually I saw a picture - albeit a very jittery one. Each time I turned on the computer the screen would be black for several minutes, but then would show a jittery picture which would settle down the longer the machine was on. Over the next couple of days this transitioned to starting with a jittery picture rather than a black screen, and ultimately to a rock solid display from the moment I powered up.
I'm not sure what caused this strange behavior, but hopefully something as simple as leaving your machine on for a while will help like it did for me. Good luck!
