HP.45 Keyboard - Dead Row


Recently purchased a nice HP.45 calculator on the Unmentionable Site.

The only issue is that no keys on the bottom row register when pressed.

Disassembled unit, and found no issue by visual inspection (broken trace etc.)

All LED segments light up OK.

It appears either the bottom row is not getting "strobed", or the return from that row has an issue (either electronic or mechanical).

Any ideas would be appreciated.


John Stark


Hi John,

I am not familiar with the 45, but you should be able to find all the information you need to trace the correct line all the way back to the CPU chip. The following will help :

1. Tony Duells article Inside the HP45 gives some good background to the HP 45 internals.

2. The PPC DVD should have the circuit diagrams for the 45 (it has the circuit diagrams for the HP 65). You need to contact Jake Schwartz to purchase the DVD, see PPC DVD

I hope that helps.



I recently disassembled and cleaned my 45 and found a few cracked solder joints on the long gold pins that connect the two boards. Use a magnifier to look for cracks and use a clamp to hold the pins straight while resoldering.


Thanks to all for your help !

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