Hello, I have a ps2 trackball, that when plugged up only goes up and down. I also have a ps2 to usb adapter and I get the same result. There is no left and right movement. the trackball lights up as well. Are the rollers inside the trackball dirty? Anything else I can try?
If the cursor is wobbling back and forth one pixel, that is an indication that one of the optos is either blocked or bad.
i.e. If data line A is stuck low and line B is alternating high/low, the mouse encoder will interpret that as wobbling back and forth between phase 1 and phase 2.

If there is no left/right motion at all, here are some possible causes:
- Roller is stuck/not turning.
- Encoder wheel is not properly secured to the roller. (roller turns, but not the encoder wheel)
- Encoder wheel and/or optical board are not properly positioned so the spokes of the turning wheel block, and then un-block, the path from the LED to the sensor.
- Both LEDs or photodiodes for that axis might be blocked, burned out, or not getting power.
-- You can do a visual check using a digital camera-- the wavelength can't be seen by the human eye, but can be seen by a digital camera.

Scott