HP28S Battery Cover Preventative Maintenance?


I recently added a US-made HP28S to my growing little collection, and it is a nifty gizmo to be sure.

I have heard about the battery cover problems and on inspecting my acquistion I can see why.

The N batteries are in the receptacle under tension from the springs, maintaining ongoing force against the inside of the cover to close the circuit. The cover is held in place by thin metal edges sliding into grooves in the plastic and the whole thing clicking in place. The tension on the upper groove seems supported only by an little bit of plastic casing that comprises the upper right corner of the calculator. I am no materials scientist, but the assembly looks like an accident waiting to happen.

I am wondering if any experts in this model know of any tricks or strategies to avoid problems before they start. For example, are there ways to ease the tension in the springs so that the circuit remains closed yet the pressure on the cover is less? Or, is there a way to reinforce the corner of the case in such a way that doesn't compromise appearance yet lowers the risk of breakage? Finally, if it does break, how have people repaired it?

Grateful for advice. I would hate to come home one day and see this thing popped open like a jack-in-the-box.



The failures i have read about here seem to have occured while changing the batteries.


I have a 19B 11, which has the same case and battery cover design as the 28. I had to resort to scotch tape to keep the battery cover on as I don't want to lose any of the programs installed on the 19B when the cover accidentally comes off and I am not able to put the cover back on in time to save the programs. Black electrical tapes works also. It isn't an elegant fix and probably not suitable for collector calculators, but it does work for a "user" calculator. Hopefully someone will have a neater solution.

best wishes



Is there some way to cut down the spring to reduce its pressure while maintaining enough pressure to keep the necessary electrical contact? It seems the spring is just too hard or large.


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