Trackball oddity

[mugwump]

I installed a new Oscar Controls spinner today which is working just fine but all of a sudden my trackball has started to flake out.  It works properly up, down, and left, but rolling to the right results in almost no on-screen movement.  Regular mouse still works fine.  Both the Benson trackball and the spinner are hooked up to a serial Opti-PAC.  Any ideas what might have gone wrong?  I've double checked to make sure I didn't yank out any wires and they all seem fine.