Inside The Hewlett Parkard HP-41C Calculator

The HP-41 is easily opened by first removeing the four rubber feets on the back cover.

Then removed the four screws. These four screws are very important. They hold the HP-41C together plus ensure there are good electrical contacts between the modules inside. This is a very clever design, unfortunately the mechanical strength of the four screw posts frequently cracked and leads to failure of an otherwise well design machine, functionality and form wise.

As show in the picture above the screw posts on the back cover at the top end of the calculator where the IO connector has broke off. This is likely the result of overtightening or the use of too short screws. On hindsight the use of some washers between the post and the IO connectors may have solved this issue. Then again these may have been lost or misplace during servicing.

It seems that the design choice for the IO connector and the contact pads for the CPU PCA was constrained by the need to make the calculator thin. Use of connectors would have raise the height of the calculator as plastic injection moulding precision in the late 1970s and early 1980s may not have been precise enough to make close tolerance and miniature connectors. No doubt using connectors and plug would have make for a more reliable calculator ( considering that the majority of failures out there seems to be cracked screw posts which leads to contact failture between the electronics modules.