Why does N64 screen go black after 1 or 2 hours of playing

Nintendo has two forms of revision numbers that they use for their cartridge games. The first one is the "-n" identifier on the end of the serial number which means that something physical about the cartridge has changed. In 99% of the cases this is an update to the label.

Back in the mid-90's we saw a lot of "-1" games appear because common games that everyone wanted to buy were being distributed when the ESRB was being instituted. There are many games that have a standard version and a "-1" revision simply because the ESRB rating was slapped on the label.

Nintendo's own Player's Choice logo is another good example of many label updates that required a new revision number because of the addition of the Player's Choice badge.

What you are really interested in is the ROM version of the game that is on the memory chip on the PCB. For quality control Nintendo does mark their games with a ROM ID on the outside of the game. For any cartridge game with a label on the back (NES, SNES or N64) there is an impressed number on the sticker. For games with only a sticker on the front (GB, GBC, GBA) the number is impressed on the game label, with the exception of the DS and 3DS, which also have the revision stamped on the back.

This number represents the facility/manufacturing line that the cartridge was assembled on. If your cartridge has the first version of the original ROM you will only see the 2-digit facility number. However, if a new version of the ROM was released from the developer to manufacturing, then a letter was appended to the end of the facility code.

The first revision will be an "A", the second revision will be a "B", and so on. If you take a look at these identifiers you can determine which version of the ROM is on your cartridges. If both games have no revision code, or if they have the same revision code, choosing which game to keep is up to you.

The ROM version can be a bigger deal than the serial number variation, depending on the nature of the ROM change. Nintendo has been known to adjust the art in some of their games for no apparent reason. Choosing which revision is a matter of preference.

You may be wondering where to find out information about specific cartridge ROM variations. The best place to go for a detailed log of variations to game ROMs is The Cutting Room Floor. (Beware, this is a blackhole for retro-gamer nerds, such as myself!)

To be clear, this site DOES NOT distribute game ROM files but they have thoroughly documented differences between the software variations of many games, old and new, for Nintendo and many other systems.

The only unfortunate aspect of TCRF is that they do not claim which revision ID stamped on the game goes with which revision detailed on their site. Instead, they just say "Japanese Version 1" or "US Version 2" when outlining differences of ROM versions. You may have to read the details on specific revisions to determine which ones may exist on your cartridges but that's never a difficult process.

The N64 analog stick is extremely unusual. It does not use potentiometers, as most other platforms (i.e. playstation controller), but instead used a geared-up digital incremental rotary encoders.

^{This is also why you have to have the control stick centered when the system turns on. Since the stick mechanism has no concept of "centered", the N64 assumes that whatever position the control stick is in when the system is turned on is "center".}

As the gearing wore down, the play of the controller progressively increased.

Wikipedia:

The N64 Analog stick does not use analog potentiometers. It uses light emitting diodes and photo detectors controlled by sensor wheels. The sensor wheels are plastic hubs which produce a shutter effect allowing for an accurate direct digital read. The sensor wheels give direct correlation to the stick position compared to potentiometers which can change resistance values over time. However gameplay function of the stick itself is not on or off digital, but analog in a sense, the more the stick is pushed the faster a game character would walk to run.

The analog stick was prone to some long-term reliability issues. If used excessively, the stick became "loose", which means it will not fully return to center position, which may render gameplay more difficult by giving unintended, non-user input to the system. This loosening can be caused by rotating it intensively - a common practice in games like Mario Party where it offers an advantage for some mini-games.