Calculator blog

Musings and comments about our common interest


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HP 41c battery bay repair kit


One of the most frequent requirements we're getting is to provide assembled repair kits for HP41C. The problem is that we depend on getting used, destroyed HP41c calculators to peel off the old flexible circuit, clean it and file off the rivet remains, and adhere the new flexible circuit to the plastic base. The issue is the first part - getting the part to perform the work.

Once you have used the part, your calculator cannot work - so you can only get it from damaged calculators that you're going to use as part donors. This is the reason that we don't get more of these assembled repair kits. 















On the other hand, it really saves a lot of time and patience to avoid folding and collating the sticky flexible circuit - I always wonder whether it is going to work properly once finished. The assembled part takes the doubt off the process!

I will post here a message once I get more assembled repair kit parts.

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Comments on HP41c battery repair kit


The repair kit for the battery bay of the HP41c (flex kit) is having good acceptance among users, but it is important to know several things upfront to avoid failing:

  • The first consideration is that this is a DIY undertaking. Some users have been put off when receiving the adhesive sheet - they expected to receive the assembled thing that you can see in the picture.
  • While it is not difficult, and it is quite short to do, don’t try to do it if you have always failed when DiY’ing! You will need to have some steady handling when adhering the film to the substrate. It is not difficult, but forget it if you suffer from Parkinson!
  • The second: you need to follow through the instructions of the installation manual, that you can find in the article. Please read them through.
  • Please make sure that you do good bends. Spend your time there and you will be rewarded with a good fit. Specially important are the negative bends, that will ensure adherence in the difficult-to-reach cavities.
  • Avoid the desire to use a sharp object to push the film to reach the bottom of the corners. You should have done better bends instead. The danger with the sharp object is that you can easily break one copper line - it has happened to me once and you will only notice it when you connect the module in the affected hole. I have it affecting module 4 in my HP41CL, but I am using only modules 1 and 2 (time and infrared, if you wanted to know). As the machine is a HP41CL, I don’t need anything else - and I still have bay three for the HP-IL when I need connection to my multimeter.
  • There is a recommendation to heat it at low temperature in an oven to get a better long term fit. It is a little more effort, but try it too.
  • The flex film is not immune to rusting. Don’t leave the machine with the batteries if you’re not using it - just like any other HP41c! The only good thing in that case is that, now, you know how to repair it!!
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HP 41c battery bay repair kit

HP 41C repair kit installed on battery connectorThe current batch of HP 41c battery connector repair kit are leaving us much faster than the first time. There was a comment in the web, whereby the user found that it was quite difficult to find the product in the search engines. I will now put it as first in the accessories list, so that it is easier to find it in the web; and also will announce it in google adwords.

If you have not seen it, I will make a brief description of it. If you have seen HP 41c/cv/cx in internet, you will find that a good number of them have rusted connectors. In many cases, this rusting impedes connection and therefore the calculator does not function. Many otherwise good HP 41c are not used and sold at discount prices, while the rest of the circuit does work (there are very few calculators that have a real circuit failure - it is either the connectors or the screw posts that are broken and do not provide enough pressure)

Diego Diaz designed a printed circuit in a foldable, adhesive material, that can be used to replace the original, rusted one. He has also prepared a short instruction sheet that make clear how to do it. So far, all users that have bought it from us have succeeded. The HP 41c repair kit is for everyone!

Be sure to download the instruction sheet that you can find in our website to make sure you don’t spoil your repair kit circuit.

You can see in the pictures that the result is impressive. However, I think that it is important to follow the instruction to “cook” it at 90º, so that the bends in the flexible circuit remain.

It is a pity that so many calculators are thrown out and discarded, when a fast, clean and elegant solution is available.

Should you think that it is still too much for you, you can try contacting us to do the repair for you at, if you are in Europe, or to if you are located in the US. They have fixed rates for repair, while we do prefer to see the calculator and then quote (in many cases a few pictures will suffice)

The HP 41c is the most successful calculator in HP’s history. While HP has never revealed the total number of 41s produced, it seems to be week over the million. Due to their robustness, many of the are still in use. And due to its easy programmability, they can still be used successfully for many applications where a graphic calculator is not required.

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