I have a Packard Bell Force SX20, 386SX-25 machine from 1992. Surprisingly, it has onboard PS2 keyboard and mouse ports. The keyboard works fine. The mouse works fine horizontally--but vertically, it moves intermittently.

I have tried three different PS2 mice, including an optical mouse. I tried to deoxidize the connector. I tried jumping the nearby fuse on the board. I tried unplugging the keyboard and using the mouse only in case it was a voltage problem. A serial mouse works OK so it's probably not driver related. It is still running the original DOS and Windows 3.1 installation.

The board otherwise works fine, except the onboard VGA output is wobbly. I don't know if it's caps or an oscillator or something else. I have been using a discrete VGA card instead.

Any ideas for fixing the mouse (or the VGA)? Maybe there's a secret Packard Bell vertical movement capacitor I can replace?