What is this video defect? (pictures)

[timmus]

What's going on in these images? This is a 10-year old tape captured with a Panasonic AG-7750 deck. The simple description is they look like occasional dark, faint, fast streaks. All the streaks that I saw seemed to have a tendency to move downward about 5 pixels with each frame, so I suspected perhaps it was a tape defect. None of the streaks lasted more than 2 or 3 frames, so this wasn't like the giant downward-moving "rolls" you usually see when you first start playing a garden variety rental videotape.

Another weird thing is that after I cleaned the heads and tried again, the same artifacts appeared, and I found they were not random. The streaks appeared almost exactly in the same tape position and frame position.

Yet when I put the tape in my AG-1980 I barely see these artifacts if at all.

Any thoughts what might be going on? Might the AG-7750 be at fault or is the AG-1980 good at covering up whatever is wrong? How might you diagnose this?

[Quasipal]

That looks to me like the drop-out compensator in the VCR operating. This sometimes replaces a missing signal with a black line.

[filmboss80]

That looks to me like the drop-out compensator in the VCR operating. This sometimes replaces a missing signal with a black line.

I agree, but I also notice that everything below that line seems to have a very slight shift in hue. See how it looks without the TBC or error compensation circuitry turned on, or play it on another VCR.