HP has ingenously design the HP-41 for very speedy production line assembly. The four screws that are use to fastern the two halfs of the case together also serves to ensure that the IO connector and the CPU PCBA make good contact with the keypad PCB. The printing wiring on the keypad PCB serves the all important task of connecting the IO connector, CPU and keypad together.
It is a well know fact that broken or crack screw posts that holds these four screws are very common in HP-41C calculators.
I just taken apart a HP41C with this problem. The reasons why the screw posts cracked like they do are very obvious. Due to manufacturing tolerence in moulding, it is quite difficult to ensure the the screw posts on each half of the casing mate properly. The screw posts that fasten the CPU board to the keypad has actually to press down on the CPU PCA in order to do this.
I just taken apart a HP41C with this problem. The reasons why the screw posts cracked like they do are very obvious. Due to manufacturing tolerence in moulding, it is quite difficult to ensure the the screw posts on each half of the casing mate properly. The screw posts that fasten the CPU board to the keypad has actually to press down on the CPU PCA in order to do this.
The simple solution is to use fiber or rubber washers at the right places around the screw posts as these pictures shows. Actually a HP service manual published in July 1979 mentioned the use of washers. But this calculator was made in 1982 and no washers were found. Could the washers have been left out during repairs?
Unfortunately I do not have access to a original unrepaired 1982 HP-41C or a updated manual to find out. But current owners of HP-41C could well be aware of the issue and the cure and take the appropriate steps could see their HP-41C giving more years of enjoyment.
In passing, here we have a fine piece of computing device brought down with a simple mechanical oversight, much like the O-rings that crashes the Challenger space shuttle.
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