Vertical scanline using s-Video, not composite? (PAL)
 

Here is my situation:
I'm trying to digitize some old VHS tapes.
For playback I am using an AKAI PRO GX4-HF (Head)

I'm using a breakout connector for SCART -> Composite/S-Video.

When using composite the signal looks fine (although a bit noisy and blurry as is expected) while when using S-Video I get a weird vertical scanline? The examples are from the menu of the VCR (it can do pre-programmed timed recording and stuff). When watching an actual VHS the scanline is slanted and quite a bit faster (no video provided yet, but can do later).

What I did so far:
- Replace breakout connector with a new one
- Tried a different recording device (I'm using an easycap because I had it lying around). The same scanlines show up using an "Elgato Game Capture HD" with composite/s-video cable adapters. (Though the elgato flickers and seems to lose sync very often). The signal itself is rock stable using the easycap.
- I tried another source (in particular my SNES) with composite as well as S-video. No such lines on s-video here.

What I didn't try:
- Replace the S-Video cable. I'm using a male<->male s-video cable between the breakout and the capture device.

My question now is: Is the VHS just "not good" or is this maybe some interference from something?

Thanks in advance.

I'm 99% sure that VHS VCR won't have S-Video output, that's only really a thing on the Super-vhs machines, and some late dvd-recorder/vhs combo decks. The Scart adapters are just passive and connect the pins that would be used for s-video (of which one is the same as used for composite hence the weird signal), but you won't get S-video out from scart unless it's explicitly enabled and the device supports it.

Both samples are noisy with the difference on S-Video that has a vertical bar floating horizontally, Typical unshielded low quality cable, Get a brand name one from back in the day, avoid those Chinese crap ones, Most of the time they are not coax, not shielded and often pinned wrong which created potential for ground loops.

You might be onto something there.
I noticed that I don't get any signal with a direct SCART->S-Video cable. First I thought the cable was just broken but in hindsight it might be because S-Video is actually not a thing on this VCR.

Thanks!