Repair in old HPs - things to avoid

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Repair in old HPs - things to avoid

Due to our work in converting HP41c into HP41CL, we have had to buy many calculators in internet. This has resulted in a number of calculators that were in less than pristine state. In fact, many of them had been repaired, and had fallen in the same traps again and again (by the way, the same traps I fell myself when starting, until a friend took me out of that ignorance!)

The typical part that always breaks first in a HP41 is the lower screw posts. The second is -guess it?- the upper screw post, but this time not the support in the main body of the calculator, but the part that supports the head of the screw in the back side of the calculator.

The third part that tends to be damaged is the battery bay contacts - but we have discussed it already - see our Repair kit page for more detail and how to solve the problem.damage

And when the problem happens, everyone retorts to the typical glue these days: a Cyanoacrylate compound, that dissolves plastic and makes a mess of the rest (apart from not being too good in resistance once dried, due to the damaging of the plastic used by HP. Here is an example on our right: you can see the state in which the posts are now. 

In the versions of the HP41c that can be converted in HPCL, these posts are abosolutely critical to ensure that the board and the main body of the calculator make good contact. 

On the other hand, a calculator that seems to be completely broken can in many cases be repaired with just putting good attention in fixing the posts, so that even pressure is achieved.

It is good practice not to tighten too much the screws once repaired. No only due to the possibility of breaking them beyond repair (you need to be aware that these calculators are 30 years old already!), but because it affect the much-loved HP keyboard feel! The difference can be appreciated between keys in the middle of the keyboard and keys just above the posts. This is not too agreable!

Coming back to the repair. The key for avoiding the problem just cited is to use a "hybrid" type of glue. Here below you can see an example that works well:

aglue This product does not dissolve the plastic and creates a lasting bond. Test it!

 

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Más sobre: HP41c, Repair kit, glue for repair

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