Every now and then I would read about (or see on Ebay) how someone's HP48 lost some columns/rows of pixels, or the ON key dieing out. I happened to receive such a calculator (HP48SX). This thing had ALL BUT THREE rows of pixels missing! About half of the keys didn't work! I fixed them both! Now I have another HP48SX with a fully working keybaord and all pixels returned to working order.
It seems that most of the keyboard problems, and missing pixel problems can be attributed to a combination of dust and/or being jostled around. The only electronic connection between the top part of the HP48 (LCD and keys) and the PCB are three rows of connectors. Two are for the LCD, and one for the keyboard. The PCB is held onto the top portion by 6 twist-prongs. They are also resonsible for connecting the top part of the HP48 to the PCB. If these are loose there is dust, you get columns of missing pixels and possibly dead keys.
Just a bit of dusting off and adding a little bit of extra solder to the connectors to adjust for any possible gaps that may have formed over the years and your HP48 is back to being functional!
Edited: 21 Nov 2005, 4:53 a.m.