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Flex circuit installation for the HP41c calculators

We offer two products to repair the frequent corrossion on the battery contacts. The most frequently sold is the complete assembly - it is ready to be put in the HP41c calculators as it comes. This is the version we recommend to our customers.


However, some of them are more adventurous or more daring, and that decide to go the extra mile and assemble it themselves. for them we have the naked Flex circuit. 

However, I'd like to give some comments from my experience of assembling more than 60 units myself:

  • If you paste the circuit onto the original plastic piece, be aware that sooner or later the contacts will peel off the plastic. There is a solution for that: using our set of 3D printed pieces, the circuit is secured mechanically to the support, with fixing pieces and a total of 8 screws per part.
  • You need first to remove the original circuit. You need to use a X-acto type of knife, and remove the rivets that fix the circuit to the plastic. I usually then cut the circuit by the contact area, and use the freed area to grab it and pull out the rest of the circuit.
  • Clean well the plastic piece from the grease that usually can be found inside the calculator. 
  • Pre-fold the flex circuit:
    • On a table, lay the circuit with the contacts side on top and the while paper down, leaving the funnelled part far from you.
    • image6-2
    • Fold upwards and away from you, and create the two bends that will be the part between the four module contact tabs. These folds should coincide with the short sides of the two circuit opening. Do not fold anything else yet.
    • image8-1
    • Turn the circuit face down. You have now the white part facing up.
    •  Partially peel the paper until the second bend. fold it there.
    • image9
    • Start adhering the circuit to the plastic from the extreme, in the side farther from the battery contacts. Ensure adherence everywhere with a non-sharp tool.
    • image10
    • Fold the circuit by hand on the top of the first tab, and push the bent part into the "valley" between both tabs. With the tool, press the bends you did at the beginning against the "corners" of the valley. The white part still adhered to the circuit should have helped you entering the circuit in the "valley". 
    • image11
    • image12
    • Now you can remove the paper altogether. 
    • image13
    • Bendthe circuit over the second set of tabs. Ensure adherence with your tool, and create the next bend.
    • image14
    • Now paste the battery contact part to the small contacts tabs. 
    • image15
    • Paste the rest of the circuit in between
    • image16
    • You have  finished! Now let's ensure it stays put: you can try with memory modules in all four tabs, to make sure the circuit is pressed against the plastic.
    • If you choose all our parts, including the base and the two fixing parts, you can further secure the circuit with a couple of pieces with screws:
    • image17
    • Leave overnight

And you're done!


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