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New piece for repairing HP41c broken lower posts
07-19-2021, 10:21 PM (This post was last modified: 07-19-2021 10:27 PM by Divasson.)
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New piece for repairing HP41c broken lower posts
Old methods to repair broken post are to glue them (but this doesn't hold together too long) and to tie them down with very small gauge copper cable, applying pressure so that it holds together. This may solve some cases, but not when the screw thread has been destroyed - maybe due to strong tightening of the screws.

Other repair methods have been proposed, including drilling down the screw post and putting in its place a cylinder with screw path, glued in place. We tried this method but there was a problem: the torque used to secure the screw resulted in cracked glue and the cylinder separating from the substrate - every time.

Our method was devised with three goals in mind:

1. Try to avoid the torque from the screw forcing on the glue with the substrate
2. Try to ensure that the front part of the calculator is pulled up when screwing the back side on.
3. Try to be compatible with all known zebra connectors - including our own.

The piece that we have designed requires drilling the old posts to the keyboard circuit level plus 3mm, taking care of leaving the hole clear, and avoiding piercing the calculator top!!. We use the drill at minimum speed:


The piece has two claws that clip in the holes we just drilled. We glue all the lower surface of the piece and the clipping claws.


When gluing the piece, there are several precautions that need to be taken:

• Be sure of covering the zebra circuit part with tape -we don't want the glue to cover it.


• Cover also all nearby pin holes of the keyboard. If glue comes into one such hole, the key will not register. In severe cases, the key will be down all the time, glued in place!

(to be continued)
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New piece for repairing HP41c broken lower posts - Divasson - 07-19-2021 10:21 PM

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