Hello,
I've had this console with built-in games for almost 20 years now. It developed this problem long ago, but I never paid it any mind... basically, at the slightest touch, the game screen either goes black or changes the game to the next one in the memory. However, I was just cleaning it yesterday and felt like playing, and the problem soon became unbearable.
(these are the front plastic covers, if anyone's interested in knowing what it looks like)
It is an old model with built in games and four switches: Power, Game Select (which changes the current game), Player Select and Game Reset. So I opened it up, checked the board and found that the "Game Select" switch is completely loose; the soldering is still there, but it has come "unglued" from the board, causing the switch to move around. I suspect this is what's causing the problem.
I tried to repair it with tape, as you see above, but it didn't work. I didn't find any other problems with the circuit board (I may have missed something), so I'd like to ask your opinion, if this is what's really causing the problem and how better to address it. I don't currently have any soldering tools, but I suppose I could manage to borrow some if that's required.