Some games not working on my FDS.

[BravesFan1966]

A couple of months ago, I bought a Famicom with its disk system. When we got it, the store I bought it from told me that the guy who sold it to them said that it had had some problems. I am fairly sure that he said the belt was replaced. It has been very hit or miss, it will play all the games for a day, and then it won't work for a month. This was weird, but recently it has changed. One of my games will play, an official copy of Doki Doki Panic. One of my games only works on side a, a reprint with all night Nippon smb on side a, and smb 2 Japan on side b. Finally, my other game doesn't work at all, an official copy of the Legend of Zelda. Also, when I try the Zelda disk, it gives me three different error messages each time I try it: 21, 22, and 25. I'm very confused , any idea what's going on?