HP 21 display is just red dots.


I got my original HP21 going with a new battery pack about a year ago. But..

I left it in a drawer for about 10 months. Now the battery seems to heat up while charging, but the dusplay is just illuminated red dots and no keys function any longer.

Any ideas, that might help me get it working again?



It sounds like your battery pack is bad. You can test the machine with two AA alkaline cells... just don't try to charge them. If your pack is bad any battery store can rebuild it... probably less than $20.


First of all try to use two alcaline batteries instead of the originals. If it works it means you have to change the battery pack´s cells with new ones (you can use NiMH or NiCD AA cells).
It´s not so difficult. You can find a tutorial in the hpmuseum home page.

Good luck



you may experience soem dificulty on positioning the batteries out of their original pack. If you want to, the best you can do is openning the original pack and place the new batteries in there. For testing purposes, the original spring is enough for closing the batteries circuit, but soldering them is a better long-term solution.


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