Hello all,
This is my first post, so, I apologize if it's in the wrong forum, but this looked like the appropriate place for this topic. All my research online can't seem to yield a workable solution for this problem.
This started about four or five days ago. I was playing my front-loading NES, model 001 from 1985 when I discovered horrible looking wavy lines pervading the screen. The actual game graphics were totally fine, but, it looked like there was a problem with the composite cables I was using. The screen basically looked like this:

I always have my NES plugged directly into my 46" Samsung LCD (as I do all my other game consoles). My first instinct was to try a different set of composite cables, but, it didn't solve the problem. Next, I tried it on an old CRT television with the NES RF Switch, but, it had the same issue. I tried it on another LCD, but, same deal.
After doing some searching online, I came to discover a lot of people suggesting it was a problem with the power supply. I always use the official NES AC adapter, but, it was plugged into a power bar, so, I tried plugging it directly into the wall outlet. The problem didn't go away. It was also suggested elsewhere that it's possible there was a problem with the capacitors. Being no expert in soldering and my understanding of how circuit boards and so on work, I figured the next best alternative was to swap out the motherboard from another NES with a non-functional 72-pin connector into the one I was having problems with since the pin connector on the one I always use is totally refurbished. After making the swap and using a different official NES adapter, the problem appeared fixed! The wavy lines were gone and everything was back to normal...
However, two days later, I went to play the NES again, and the wavy lines had returned! How can that be possible? After making the motherboard swap, which included the capacitors, it was basically a completely different NES. The swapped out motherboard was from a later model of the NES, specifically a Mattel Canada variant. The original was from launch in 1985. It seems very strange that two completely different motherboards and setups would decide to experience the exact same problem within a day of each other.
It was suggested on a YouTube video comment section that possibly swapping out the power/reset buttons could solve the problem. However, after I attempted that, it didn't help. The wavy lines were still present.
I'd like to know exactly what causes the issue to crop up, if possible. I've had my NES setup like this, basically unchanged for almost six years. Why would it suddenly happen like this? And, short of going to a top-loading NES, is there any other solution I can try or changes I can make to the environment to possibly remedy this situation? I'm not sure if this is related or not, but, when the problem happened again on the swapped-out motherboard, I tried the RF switch again on the CRT TV and it the sound was making a horrible buzzing noise that didn't happen before. Like I said, I don't know if it's related to this problem or not, but, it might be another clue.
I'm basically out of ideas. Any comments or suggestions would be appreciated.
Thanks!