HP 32S Repair

[kriskim]

I found a way to permanently repair the keyboard, but it's not for the faint of heart. I love the result, though. I recently repaired a dead HP20S that I bought online. The machine showed signs of liquid damage. The keyboard had one column of keys that did not work, as well as an unresponsive ON/C key. Dissasembly of the calculator showed that the kwyboard circuit sheet had broken traces--their fragility due to the fact that they are made of graphite printed on a plastic sheet. I tried using a silver conductive ink pen to reform the broken traces, but it did not work. So, I tried a radical solution: replace the keyboard with discrete tactile switches, available from Digi-Key and many other electronic component suppliers. I removed all the old plastic sheets and covered the steel keypad plate with Kapton tape cut from a 3d printer buildplate cover (3 mil polyimide adhesive-backed 10"x10" sheet from Micro-Center). Then I used double-sided tape to cover the areas where the new switches would be placed. 30 AWG magnet wire (or anything with finer gauage will also do) was cut to length (~.5" to 1.5")and soldered onto the appropriate contacts to replicate the switch matrix layout of the original keyboard. The graphite coating on the LCD diplay/processor board keyboard contact fingers was removed using a scraping tool and cleaned of any carbon residue using 70% isopropyl alcohol (IPA). Solder was then applied to the bare copper surfaces (15 fingers in all). Longer lengths of magnet wire were attached from the rows and columns to the contact fingers. The results are shown in the attached pictures. I used a switch rated at 100g of activation force (E-Switch p/n TL3315NF100Q). I found this to be a bit too responsive, so I plan to use a switch with a stiffer rating next time.