Atari 7800:Atari 7800 Model Differences
Page content & researching taken from io55.net's Atari 7800 page with permission, in collaboration.
There are 2 released models of the 2600, and 2 minor/internal revisions for 1 of the 2 models.
Models
Models are arranged chronologically.
“7800 (1984)”
The original run of the 7800, which had to cease production later that year due to contractual disputes. Sold only in southern California at first. Upon the 1986 relaunch, all overstock from the 1984 run was sold, but it is unknown if sales were still limited to California or not. The only noteworthy difference to the later run, is the presence of an unused expansion port on the left side.
“7800 (1986-1992)”
Identical to the 1984 run 7800, except the expansion port is now gone.
Revisions
There are two revisions within the 7800 (1986-1992), and no revisions within the 7800 (1984).
7800 (1986-1992) revisions:
“Atari 7800” without expansion, with indent (1986-19??)
Outside of a minor motherboard change, this Atari 7800 version has no expansion port anymore. However, there is an indent located where the port used to be. This version may have a minor incompatibility with “Dark Chambers”, a 2600 game.
“Atari 7800” without expansion or indent (198?-1992)
The exact same as above, except either a small outline or nothing at all replaces the expansion port indent. Aforementioned “Dark Chambers” defect may not exist, however, games using FE-bank switching may be incompatible instead (Centipede, Kool-Aid Man, etc.)
References
https://en.wikipedia.org/wiki/Atari_7800#System_revisions
http://www.ataricompendium.com/game_library/easter_eggs/7800/78prosystem.html