Run Sound3V to turn on PCjr 3 voice sound. This is necessary for some Tandy 1000 games that aren't set up properly for the junior's audio hardware. It essentially forces the beeper sound through the PC speakers, rather than the monitor. Unlike the jr, the Tandy 1000 mixes the 3 voice sound and beeper through the monitor's speakers at once, whereas the jr can only run one or the other, not both at the same time. 

It can, however, play the beeper music through its PC speakers at the same time, giving it the ability to play all the same music as the Tandy. It just has to be set up properly.

Run SoundI to reset the beeper mode. You're going to want this for games that use PC beeper sound only.