Posted Fri Mar 19, 2010 12:46 AM
Unfortunately, the original Intellivision Master Component and INTV System III consoles aren't the easiest machines to work on. It is possible to open the console and swap the controllers, but as I recall, you have to desolder and remove the RF shielding to expose the connectors (they're little nine-pin headers at two corners of the board). You may also have to do some untangling, as one of the controller cables is coiled up with some power wires going to the switch.
I would start by opening and cleaning the affected controller. The Intellivision controller is made of layered mylar sheets, similar to those used in computer keyboards. If some dirt or residue has gotten between the conductors on these layers, you should be able to swab them clean. Fortunately, the controllers are screwed together, so they're not nearly as difficult to get apart as the Intellivision II controllers.