CX80 not working in all directions

I just bought a sealed CX80 trackball from eBay and found that it does not work in all directions in joystick mode. It seems to scroll left and right but will not work up and down. I have an different CX80 that works in all directions but doesn't scroll as smoothly as it was left to rust internally. Is there anything anyone can recommend I try? I have tried it on both the 7800 and a Flashback 2 and found that it was behaving the same on both consoles.

Thanks!