HP21 LED and keyboard problems

[thib]

Hello,

I have a 21 with LED and keyboard problems. Some segments of the LED's are constantly lit (but not so bright as they should be). The display is therefore unreadable since the numberes are not properly drawn. Moreover, there are some keybord problems : for instance, the "4" keys only works once every ten times... Finally, I replaced the burned batteries with regular AA cells. Do you think this may cause the problems? Thanks in advance, Thib.

[Dan Grelinger]

I have never seen an HP-21, but have taken apart LED calculators. One reason for LED segments being continously lit is that the calculator has suffered a severe shock, and the fine (and uninsulated) LED connecting wires have been bent and are touching another conductor. Normally they will appear much brighter than normal, since the segment is full on, instead of being strobed, as normal. So you may have another problem perhaps with the display driver. The button problem you describe is not uncommon, and is normally a dirty or worn contact. I doubt that the battery change caused either of these problems.

[thib]

Thanks a lot!