HP-42S repair of unresponsive keyboard


Hi all,

I found an HP-42S on the auction site at what seemed a good price. When it arrived, the rightmost column of keys was unresponsive (I got a decent refund from the seller, no complaints there), and decided to attempt the repair.

The keys would work when pressing down on the bezel below the screen, so the problem was with the foam below the plastic tab with the keyboard connectors no longer applying the necessary pressure to ensure connection.

Opening the case was a bit harder than anticipated, drilling out the four heat stakes on top was simple enough, but getting the lower four to pop was trickier (I guess I don't have strong enough fingers). In the end I had to use a broad-blade screwdriver for this part. I managed not to damage the PCB, but the case is not as pretty as it once was.

First attempt involved placing a piece of plastic film (cable shrink) below the plastic tab. This gave good connection, but it built a bit too much, so connection to the middle columns of the screen was lost.

Second attempt involved placing a piece of foam between the PCB and the back of the case and closing the case with some pressure being applied to the PCB from behind. This sorta worked, but not as reliably as I would've wished, nor did the case close back up properly.

For my third attempt, I again tried building a bit under the plastic tab. This time, I cut a much narrower strip (about 3 mm) and inserted it deeper. It is situated such that it bends the plastic tab towards the PCB, but does not sit directly between the foam and the plastic tab where the latter makes contact with the PCB. That appears to work well. All keys connect reliably, and the case closes up without undue stress.

Reassembly is tentative. The halves of the case sit together, but there is a small gap on the lower end (I cut too much off the lower heat stakes before reassembly, so they don't hold together the lower half anymore) and I have not found screws small enough that I dare screw them into the upper heat stakes to secure the top. I guess this one will live on a desk and not travel anymore. If I feel adventurous, I might even attempt the double-clock and/or 32k memory upgrades one day :-)

A great thank you to all who have posted their experiences with Pioneer repairs here before, I would not have attempted this repair without you!



I have found a thick rubber band works great placing under the existing flexible PCB.

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