See 'squares' on my LG LCD monitor

[Snowwie]

I have recently bought a (second hand) LG TV/Monitor type M1917A.
Click this link to see my setup.

This monitor has a SCART input, which I use for my Amiga 1200.

I use a normal RGB->Scart cable, but I notice faint squares on screen. Also, when showing a black screen I see some interference.

Is this due to lack of cable quality? Or is just the low 15Khz output of the Amiga and the relative big size of the screen (19") which creates this effect?

[Snowwie]

I suspected it could be the cable, because I have seen that scheme before and the connections in my cable are different.

Now I do have to make the decision whether to solder the cable to correct specs, and buying 3 kinds of resistors + adding transport costs, or, just buying a new one from Amigakit. I am not sure those have ferrite cores, but neither about the cable I already have.