New solution for the corrosion of HP-41 I/O block.


Hi all,

I've managed to built a suitable solution for those bad damaged I/O blocks we've all seen into lots of HP-41's battery compartment.

Please take a look at:

Your comments are certainly welcomed.



Hi Diego:

That´s the best solution that I have ever seen. It looks great. Just wondering if the adhesive is strong enough. The original flex circuit is assembled with plastic rivets.
In my opinion some tiny screws will increase the durability.

Great work ... again ;-)



Very cool! What will they cost?


Hi Diego.

Let me be among the first to say thank you for the development of this item. I have long waited for a solution such as this, and just two weeks ago I lost my fave 41 to this disease.

How to order?
How much?

Congrats again.


Positively brilliant. The VHB adhesive does the job very well I'm sure without the need for screws or rivets.

Do you have any quantity pricing?


I am eager to order some of these as well.

However, I am wondering if the VHB adhesive is too strong and will make future repairs impossible... after the new circuit is attached, how difficult is it to remove it?

If it is difficult, perhaps using less than 100% coverage of adhesive would be appropriate? (Or perhaps it is already that way?)



Hi James,

3M VHB is AFAIK the strongest double sided adhesive tape available. However, it can be removed. I've done this in one of the samples (in the keyboard PCB contact area) with a smal drop of oil... and a nice amount of patience...

Should the case of a later replacement arises, it will be possible to get the I/O Block plastic cleaned to receive a new Flex PCB.




Hi Diego,

3M VHB is AFAIK the strongest double sided adhesive tape available.

Did the tape help you to withstand the powers of the recent tropical storm on the Canaries?



Hi Marcus,

Good point indeed! :-)

But unfortunatelly, we haven't got enough tape to securely bond every antenna... and power line tower... more than 200,000 people sunk into darkness, rotten foods, closed highways, no phone lines and almost out of tap water for four days. A real mess. The worst part of all that happened in the Teneriffe island, here at Gran Canaria, where I live, there were almost no significative damages affecting people's normal life. There were severe damages to the harvests though.

This was by no means comparable to Rita's or Katrina's destruction path thru the States, but this was the first time something like this happened in the Canaries and we were not ready at all, so we've paid a very high price for joining the "Hurricane Club".

I sincerely hope we've all learned that first lesson and next time (if ever) we'll be more prepared to face Nature's power.

Best wishes.



Another fantastic product Diego!!! I'm sure you've just saved the lives of many, many ailing 41's.

I'm not sure how many I need yet, certainly 2 but maybe more. I need to check with my two sons’ in Japan before ordering - I'm guessing they both will need one as well. I'll eMail you once I'm sure.

Keep up the great work; I'll be anxiously awaiting the next in what seems like an endless line of incredible products from the Canaries...

Best Wishes for the coming Holidays,


Excellent! Put me down for a couple!


--- Les




Let me add my voice to the chorus of "way to go!" coming from the gallery. Way to go, Diego! 8)



Very cool.

I'll take a couple. Can you post price & ordering info? Thanks.


Incredible work ! I want 2 of these. Please let us know if this makes it to production status. Congratulations on your dedication to helping others.


Dear Diego,

a really great solution from your side for the world of HP41 enthusiasts. Now this is your second Xmas gift :-))

With best wishes - Christoph


Yeah D, I'm in for a couple too!



Brilliant work I agree.... Thanks for your work again Diego.

I´m currious about the ebay deals with dead HP-41 calculators... ;)


Hi again and a very big thanks to all of you for your kind comments... (Seems you were rigth Bill ;-)

I'd like to clarify that these units are not in production yet. If this was the case I'd have placed a FS ad instead.

These are samples I ordered a few weeks ago and received yesterday for testing. Tests have gone really well. I was the first one to be impressed for the outstanding quality of the board and the accuracy of the tooling job (this was my real concern as tolerances for the I/O interfece are very tight)

The aim of this thread is making myself a clearer idea about the "reasonable" number of units to order mass production. Obviously the final price will depend on that number... the higher the number, the lower the price (ok, you knew that already :-) import taxes will also affect the definitive figures.

The expected range for the final price tag is set between 35 and 45 Eur. As you can see they're not cheap, (more than $1000 just for processing and tooling... three samples!!) that's probably why no-one had decided re-manufacturing them before... that, and the difficulties in find a high quality manufacturer willing to accept so small a run orders... most HI-Tech manufacturers of Flex-PCB's do not accept orders below the thousand units.

Regarding availablity, they can be ready to ship by early Feb. I'll place the corresponding FS ad with the usual info in this site as I got them on hand.

Again thanks for your interest and best wishes for this Xmas season from the (now sunny :-) Canary Islands.



Diego: Here, here!

I've also a "dead" 41C. Well, not really dead, but with corroded contacts. If I could change them, I could give it a second life!

Count me in, I too I'm looking forward to your offer.

Have a nice Xmas.



Hi Diego,

Congrats to this superb job.
If I can help to decrease the cost: I need five!

Best wishes,

P.S. How many top secret "little surprises" do you still have in your drawer?


The picture of the contacts on the installed one looks different than the flat one. They appear much too thin. Did you have two versions made?

BTW, I have a box of 24+ HP41 machines: all working, but with repaired corroded contacts and many with minor engravings, etc. It may be worth fixing them up with new contacts.

Now, tool up some port and battery covers...


Hi David,

You've certainly got a sharp eye man!!

The flat Flex in the picture is indeed thicker than the mounted one. This is due to the liner (protective paper coating) attached to its back. This liner must be removed during instalation to expose 3M VHB adhesive, thus the final thickness is actually thinner, but there is just one version of this Flex PCB.

If you're seriously planning a *mass* recovery of your (+24) units, chances are that this helps to get a "thinner" final price for all of us too. ;-)

Best wishes.



Well, I was referring to the width of the traces where the modules make contact. On the photo of the mounted one, they appear to be rather thin. On the photo of the flat one they seem to be more like the width of the original HP ones.


Hi David,

Thanks for the clarification, I had been wondering how have you got such a sharp perception to appreciate the difference in the PCB's thickness... (and was seriously considering a visit to the optician!! :-)

Back to the tracks widthness issue, the difference you can see in the picture is just caused mainly due to illumination incident angle when the pictures were taken, but both PCB's are identical and have been designed to match (or exceed) the original specs.



Edited: 10 Dec 2005, 12:56 p.m.


If the price is reasonable, I would be interested in purchasing about five. Any idea yet what the price would be?

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