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Calculator blog

Musings and comments about our common interest


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HP41 repairs

I am repairing more and more HP41 calculators lately. I have a backlog of more or less one month - and calculators keep coming. We offer this as a service but do not see it as a business, since it is not "scalable": I have only so many hours, and they cannot be increased - except at the expense of more important things to me. 

My opinion is that most of the repairs could be done by the user himself, and only the very special cases be sent to us. Really 70% of repairs do not require specific skills or unavailable parts. Then 20% may require screen or processors that are not available - and 10% cannot be repaired at all.

We have added a couple of pages to our book "HP41 Repair", which you can find in Amazon - we really think with it you can repair most of the calculators. 

One think that is true is that more and more the plastic of the hp41 calculators is becoming brittle and more difficult to repair. The material does not seem to age well, and lose the plasticity it once had.

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More about: HP41 Repair
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A comparison between the latest HP12c and the upcoming HP12c

We mentioned a couple of posts ago that there were HP12c units coming our way in a boat. They are slightly different from the previous versions - at least the prototypes we've seen.

(BTW - did I say that they are made in the Philippines, not China?)

The new ones are more "metallic": the lettering in the back looks like metal uncovered by the black paint. Here is the upper one. Notice the additional securing of the battery cover:


The bezel looks real metal, not like the previous one, that looks a little like plastic. The small scratches on the new one are due to heavy use lately:



Is this the template for new coming products? Let's see...

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More about: HP12c, hp15c
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HP15c Manuals


We have included a HP15c Manuals page, where we link to HP15c manuals. There are several languages - including even Japanese!

You can find the page HERE


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More about: Manuales, hp15c
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HP10bII+ and newest HP12c "on its way"

We have been told by Moravia that the HP10bII+ and the HP12c (of the newest version) are now on their way in a boat from the Philippines.

Compared with the previous HP12c, the newest has the same innards (as shown in the previous blog release), but the bezel looks much more "metal" than the plasticky bezel of the last version. They clearly look better.

The HP12c is many times faster than the HP12c platinum, due to its atmel processor. It is also several times more efficient in consumption than the original HP12c+ and Anniversary - the processors are different and much more evolved when it comes to energy consumption. When I have some time, I will make a comparison.

Due to the programming model, much simpler than the HP15c, it is also significantly faster in simple programs than the Atmel-based HP15c. Go figure! Now, the HP15c has a much wider range of functions, and also much more memory for registers and programs.

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A HP12c's innards

Out of curiosity, I wnted to open one of the latest units of HP12c that I have received. This is a normal unit, made during HP's tenure in the Philippines (I think the actual producer is Kinpo, but I am not sure). Let's see what we find within!

When opening it, you have to remove the 4 feet in the corner. There are 6 screws to unscrew (do you find the sixth?). Trying to open it without unscrewing all will destroy the case.


The sixth screw is below the right battery. Careful!

Once opened, both sides are united by a three cables that carry the power from the batteries. The circuit, on the other hand, is visible in the back of the keyboard. It is very concentrated around the main processor. There are a couple of copper pads that I don't know what they are for. There are also a couple of small springs that are exceedingly easy to lose (This is common to other Voyager calculators of all vintages)



The white band below is an adhesive. again, I don't know what it is for. I have removed it and found nothing to protect below it.

The 6-point connector is a POGO 6-pin connector, but it is connected as a USB interface, as well as a reset device, by shorting specific pins. The problem is that this connector is completely non-standard. There was one produced long ago for the HP15c Limited Edition, but it has a completely different connection schematic. If you have one from that time you can modify it - but it won't work as is with the new calculators.

Is there not another alternative? Yes, it is. In the circuit there are provisions to solder a true USB nano connector. Where? in the right side of the circuit. Here:


I don't know the exact part number that can be connected here. You'd need also to break the case, or have opened each time you want to change the firmware. If you look into, you'll find that there is people around still interested on Voyager firmware mods. You could eventually want to repurpose the calculator for whatever type of calculator or functions. You have, though, the wrong keyboard for it. You would need to consider creating a silicone film with the lettering of whatever you want. 


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HP10c for repair!


The other day I had the opportunity to repair an HP10c calculator. I had not seen such model before! Yes, HP11c and HP15c are better, but the HP10c is the rarest of them all. It was a well used, worn unit, that did not work. I think that the problem had to do with dirt and corrosion, because once cleaned internally with anti-rust fluids it worked just after assembly.

I was able to make it work, though:


When opening it, it was of a more advanced design that I am used to, with a fully covered back that showed a large circuit, instead of the several smallr found in HP15c or old HP12. It also had a flexible circuit I was not used to.:



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More about: HP10c, hp15c
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File away these solder peaks!


I have been doing some repairs lately, and I have seen some full-nut modules that did not want to work. In the past, I have always classified them as defective and go with another. 

However, this time it was a CX module. This are far rarer and very expensive to get. What's more, I saw it working on-and-off before the repair. (It was a lower post repair), so it should work - but it was not working in the original repaired calculator. Others were working, thoug, and I also managed to make work the CX module on another not repaired body. What could be the problem?

Here is a picture of the lower post repair piece:


I have designed a couple of pads on the left and right of the screw posts to allow for more surface to "glue" onto the keyboard circuit. In principle this surface does not collide with any part of the circuit. In practice, it does: there are some solder points that are a little bit too high - and these press onto the pads and avoid a good contact with the zebra. I have discovered that last week and filing them away has allowed me to "save" this CX circuit - and probably many others goign forward.

The ones to file are the ones at the right and left of the connectors, and sometimes also the ones between both connector lines.


This may also happen on some cases with non-repaired units when using the zebras over the old support: I see the marks of the solder points on the surface of the film connecting the two parts of the zebra. 

I am updating also the book with these comments.

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Happy new 2023

Dear Calculator-lovers,

We wish you a very happy 2023. Hopefully, this year will come with some nice news regarding our hobby - and maybe even new HP-branded calculators! Stay tuned since you will see it here first.

Apart from whatever comes from the HP brand, you will get here at least three new HP calculator related products - specifically produced by us.

Have a nice year and take care.

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Glue for HP41 repairs

In our book we insist on using E6000 glue. This product has been stopped and replaced by the E6000+. The reason for the change is a legal (safety-based) one: there are components and odours that may be hazardous to our health in the old mix. (You can find some in Ebay still - go grab it while it lasts.)

Unfortunately, the E6000+ does not work for our application. I have used it for a low post repair and for a glued battery assembly and it does not hold for too long. In the low post repair, it is enough to impede proper working. The glued batttery assembly did not allow for very tight screwing. The material is too flexible and not adhesive enough for the material we are using. Even if I am too repetitive: E6000+ DOES NOT WORK WELL FOR OUR APPLICATIONS!!

We have heard a lot of good things about the epoxy 2-component glues, and we re testing, but the challenge with these is that you need to do a previous preparation of the glue, by mixing both components and applying the paste onto the parts. I have run some tests this holidays and I am waiting for the glue to cure to make some strenght tests. I will report once I have tested the samples thoroughy. Again, it is a pain compared with the plain E6000 !


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Valentín Albillo's Articles


Valentín Albillo is a Spanish pioneer in HP calculators. He has been writing articles about several HP calculators and computers for a long time. He has a soft spot for the HP71b, but he has written articles for most of the HP vintage models.

I had a page linking to his articles in his previous website, but now that that one is down, has hosted Valentín's articles in their website. I just had to update the links to the new site!

You can find here the page that links to all of Valentín's articles:

Valentín Albillo's articles

And here you have one of them, describing, praising and using my preferred calculator: the HP15c:

HP Article VA006 - Long Live the HP-15C.pdf


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