[spooky]

Well i must admit i've never heard of this before either.

When you say none of the games let you play the two player selection then it sounds like there may be a blown a fuse on the main board. Usualy both controllers are governed by one fuse but it may be different with the 900x series. There is also a bank of surface mount diodes that route the joypad "logic" and if one of these diodes fails then the psx could loose operation of one are both controllers.

Saying this it may be something simple like the cable from the controller module to the main board may be damaged or has not been refitted correctly.

Hope you get it sorted.