Posted Sat Jul 23, 2011 5:01 PM
The cartridge contains a POKEY chip, which is an Atari sound chip that was used in 7800 BallBlazer to create the music. BallBlazer cartridges are sometimes collected as "donors" either by 7800 programmers who want to use POKEY sound in their own games, or by others who want to remove it from the cartridge for some other project.
I'd second GroovyBee's recommendation: clean the cartridge first, and if that doesn't work, you shouldn't have any trouble finding a replacement for more than a few dollars (BallBlazer is a fairly common game). You might even find a taker for your dead cartridge if you list it cheaply enough it in the Marketplace.