HP-10BII keyboard problem

Last modified: 2003/02/11,03:00 GMT

Several people have now commented on the bad feel of the FV key on the HP-10BII keyboard. For no readily apparent reason, I took one to bits to see if there was a design or mechanical problem, and arrived at a theory that the top-right heat stake, which comes right under one of the two hinges for the FV key, might be putting that key under some kind of consistent mechanical stress that leads to, for example, a slight (but significant) misalignment of the key. This could be in the plane of the keyboard, but could also be along the axis perpendicular to the underlying main circuit board, such that (for example) the key travel becomes just too much or just too little, given the design parameters of the plastic domes in the keyboard.

Anyway, I posited this theory on the HP Museum site discussion forum, and was promptly asked if I could take some pictures.

So here they are. Excuse the fingermarks; I've handled this machine a lot, and didn't particularly anticipate ever using it again.

The four heat stakes on the back of the 10BII, before opening the unit.

The two halves of the unit after opening, front half on the left.

The front half of the case separated from the main board, which still has the keyboard attached. The arrows point to where the two heat stakes from the keyframe attach it to the main board.

A close-up of where the heat stake from the top-right portion of keyframe mates with the hole in the main board.

A close-up of where the heat stake from the bottom-left portion of keyframe mates with the hole in the main board.

From left to right, the main board showing the keyboard contacts, the plastic sheet of little conductive domes that provide both the click and the electrical closure on the main board pads, and the one-piece plastic frame that carries all the keys.

For comparison, here is an unopened 10BII alongside the plastic keyframe and the main board.

A close-up of the back of the keyframe showing exactly where the top-right heat stake is, and how close it is to the hinge of the FV key.

A close-up of the back of the keyframe showing exactly where the bottom-left heat stake is, sitting on an intersection of plastic sprues away from any key's hinge.

The top of the main board, with two holes circled; the right one is the hole for the top-right heat stake, but the left one is unused.

The bottom of the main board, with two holes circled; the left one is the hole for the bottom-left heat stake, but the right one is unused.

Please direct comments to the HP museum forum. Commentary from experienced mechanical engineers and their ilk would be welcome.