HP 33e repair


I recently acquired an HP 33e (serial #1835A08027) that hadn't been used in some years. The positive battery contact was broken off, but I was able to power on the machine with a bench power supply. At first, almost none of the keyboard keys worked, and the display was very dim and displayed nothing but fives. I disassembled the entire calculator, and cleaned all the ICs and the flexible circuit board with contact cleaner.

After that, the display now works properly and is bright, but some of the keys will only work if you squeeze the unit together or push down on the faceplate near the key. Any suggestions on this? I've thought of trying to bend out the legs on the ICs a little bit but am afraid that one would break off. Would throwing a piece of cardboard into the back help? Also, for the battery contact, I have suitable metal, but does anyone know where I might find a screw and nut of the right size? The only sources I've found so far have a minimum order of around 100, way more than I need.


Does it pass the STO ENTER self-test? Usually if the problem is bad contact between the IC terminals and the keyboard traces you will get an Error 9 instead of all 8's. The problem could be in the snap dome circuit traces, which sometimes crack or the solder connections between the snap dome sheet and the keyboard. I tried re-soldering a bad connection once and ended up ruining the keyboard, but my soldering skills are not very good.


Yeah, it passes the STO ENTER test. When I do that, the screen goes blank for about a second, then all 8s, commas, and the negative sign on the far left appear. Also, the keys that act up are very random, it's not always the same keys, it's never one line of keys straight down or anything, all the keys work at least some of the time, and pushing down or pressing the key harder will make it go, which makes me think that possibly there is too much space between the snap disks and the keyboard, caused by old foam.

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