USA NTSC SNES PICTURE PROBLEM / SCREEN LINES

Just wondering if anyone here has any idea what is causing this problem. So here's the issue. -
PAL CRT TV(60hz capable)/USA NTSC SNES
After a few minutes of powering on the screen starts displaying parallel lines. It starts gradual and not really noticeable at all. The lines get thicker as they rotate clockwise. I have included some photos to give you an idea. One other thing that is strange is that out of testing maybe 60 games, there is two games that seem immune to the problem; Yoshi's Island 2 and Rockman X2. Maybe it has something to do with the unique graphics chips in these games.

Connected to PAL CRT TV with official Nintendo AV cable. PSU's that I have are a megadrive model 1 PSU with a homemade adapter and a cheap variable AC/DC two pin. Don't know if it's worth to mention but when I use the MD PSU the lines are not parallel but are "flared" around certain points in the screen - the time between lines showing and powering on is exactly the same. The gradual picture degradation/increasing of line width remains the same as well.

A photo below to give you a better idea: left(just powered on) / right(5 minutes later) ***the exposure has been increased in the 2nd shot only so that the lines are clearly visible.

 

NTSC Snes's need a different cable than the official PAL one.

Need caps on the RGB lines, also need the shunt resistors removing.

A PAL gamecube cable is pretty close to what the US snes needs and should work on most tv's without modification.

 

Thanks for the reply, sorry didn't get any notification of it.
I've got two official AV cables, one bought from a US seller and the other from Japan. No matter what cable I use the problem is always the same. RF, PAL AV, NTSC AV. I was thinking it might be a capacitor problem, but don't see any swollen or leaky caps. Trying an RGB cable is the only thing I haven't done. But a decent one is expensive.

Is it possible to mod a Wii RGB cable to work with the SNES ? Can't find any info about it.. But that would be very handy

 

Have got an official AV gamecube and an official SFC RGB in the post. Will update after testing them out.

- If anybody else has had a similar issue like this, post it up

*** have tested out the PAL gamecube cable and there is a definite improvement. But the lines still appear. Though a bit weaker than before and only really noticeable on solid colour backgrounds or when the screen isn't moving.