Display problems with the HP-38C


I have two HP-38C's. They have the same problem, namely that the display does funny things. I have opened one of them and found some of the solderless construction described on pages 37-38 of Mier-Jedrzejowicz's book "A Guide to HP Handheld Calculators and Computers." I can get a temporary return to proper operation by pressing on the sides of the case near the display, by twisting the case, etc. With all the crazy displays that occur I have yet to find that the internal calculations are incorrect.


Probably a bad pressure connection to the display module. It may help to disassemble the unit (make careful not of the position and orientation of the chips first), clean the circuit board with 91%+ isopropyl alcohol. In stubborn cases I have shimmed the back of the pressure plate over the contacts with Kapton wave solder tape.

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