HP-41CV

[mfleming]

A bad connection between keyboard and CPU would likely impact an entire row or column of keys. Another possibility is that debris or oxidation is affecting the single dome beneath the zero key. If debris, try using compressed air around the key. If that doesn't work, use a drop of cleaner like DeoxIT Red and then work the key to see if it improves. It would be best to open the calculator and apply the drop to the hole in the keyboard PCB beneath the zero key, but I've done a quick fix successfully by just putting a drop or two into the gap between key and calculator face.

~Mark