In case you see this jitter both on crt & lcd, then it might be interference.
In my case, I have an old 1084s which has been repaired a couple of times (amplification/sound, and display). Then I plugged the A500 with an RGB cable and I noticed those annoying lines . They were more noticeable when the display was shifted to the right using the Horizontal Position , and disappeared when shifted to the left :-?
