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Calculator blog

Musings and comments about our common interest


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Woodstock battery bay

5E6A51FF-8398-4A13-8B6B-D6A334BE1B74Now we have two battery holders: one for the HP41 family and another for the woodstock family. However, the one for the woodstock family is different. The HP41c always had battery holders that could work with separate batteries (type N - never put A24 types or you will destroy your unit! I have received many with this problem), apart from the accu-pack that HP marketed; but the Woodstock family, as far as I know, used a battery pack only - there was no way to use normal batteries - unless you performed surgery in your pack. So ours is an easy way to stop using the original pack and use cheap, commonplace AA batteries.

For the sake of making things safe, we printed the + and - sign on the pack, so that you know what should be the polarity of the battieries inserted. These come in an out quite easily due to the elasticity of the polymer at this particular thickness. It took us several different thickess 3D-prints until we found that point.

The only thing that I sorely miss is the beige color. When we designed the part, there was beige as an option - but it was taken out of the options when it was time to start the tests. Damn!


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HP4c feet for free on orders >40€


IMG_2797When I started repairing calculators I took good care of separating the original feet without damaging them, and putting them aside to reassemble after the repair. Once we ordered our own feet, throiwing away the original feet is the very first thing we do. It is a small cost compared with the image of quality and comfort the new feet give.

We ordered feet with 1.5mm thickness. We have seen original feet of all thickness, but we wanted something substantial, so that it really keeps the calculator still on the table, and makes it difficult to displace it. Also we only ship sets of 4, because replacing just one doesn't look good and there might be height differences!

Once put the new feet, the feeling of having finished the repair or assembly is complete!

So we have decided to add a free set of 4 feet to any order over 40€ in repair materials, including shipping, starting today ! You will see it if you're subscribed to our newsletter.

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17bii_6bigFor me, the HP17BII+ is probably the best hidden secret of calculator world today. I don't know why it isn't sold much, much more. It has the feature set of the original HP17BII (minus a couple of only-programmable functions for the solver that I have never used), plus a new menu for currency translation (very useful when you're analyzing a foreign company financial statements), and a much, much (did I say much) better screen. It also has much more memory that you can use  to store many solver formulas.

And this is the beauty of this calculator: the solver. While the mighty HP42s had vectors and matrixes, it lacked a simple, programmable solver that solves your day-to-day problems in a much more flexible way than the typical program. And it can do loops and ifs, if you want to spend time; but that's not its purpose.

It also has a lot of menus made for the financial user - and a math menu that frankly it would be enough for the scientist - if only it had trigonometrics too.

Let's see the menus for a while:

FIN: finance. Time Value of Money, interest compounding, cashflow analysis, bond calculations and depreciation

BUS: useful % calculations: change, total, markup on prices and margin on sales. Very easy to use and fast!

SUM: statistical calculations on one or two variables, keeping all the data sets (different from the 12c and other units that have statistics). You can go to any sample and change it. Eventually you could plot it if you had the printer.

TIME: this calculator keeps a clock and can do all kind of time calculations, and keep appointments and alarms. Like the HP41C Time Module - but much better and simple to operate.

SOLVE: here is where all your formulae are. Extremely powerful - if you know your business and set to make it easy. (Calculate prices that go according to a formula involving market commodity prices, currencies, etc. is a very simple thing with the solver)

CURRX: currency calculations. You can have many pairs of currencies defined. Once updated the exchange rate, you can easily make all calculations.

On top of all that, it looks the part too: the metal surface is quite resistant, and the plastic back extremely so. It could print, too - only if you found an infrared printer, which are out-of-market nowadays.

And the price is only 77,90€ - much cheaper than 12c Platinum!

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Más sobre: HP17bII+
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Classic charger substitution

Some customers have asked for a solution for the Classic battery. What has been suggested is something similar to the Woodstock battery holder: a 3D piece that can handle 3 normal batteries (still to be decided if we can fit AA or it'll have to be AAA) and that integrates the contacts with the calculator. All in the HP original black and with the usual HP classic fixings. 

Anyone interested? Just to know whether to devote design time to it or not!

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zebra utilization

The zebra comes with a holding harness to avoid damage. In addition, it comes with a couple of staples to hold it together too. But in order to put it in the calculator, you need to remove both the staples and the holder.

The zebra can be used on the previous support in the calculator, or even without support. In case of damaged hardware, it can be removed (provided that the screw posts remain), and the zebra be put on the screw posts - it will work all the same! The plastic of the PCB circuit is far more resistant than the original, and the connectors can handle much better the current than any elastomeric zebra (included the white ones found in some HP41c).  


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Card reader repair



Another typical problem happening with the card readers is the axis' slipping. You have already repaired the gummy wheel and you realize that the electric motor slips.

Once opened the card reader, you take the motor and pull the axis out. You will see that the inner axis attached to the motor is much thinner than the outer jacket of the screw part of the axis. (I have no pictures now but will take them on the next repair). The void between inner axis and jacket is fulled with a plastic compound that also deteriorates over time. What to do?

We have found that securing the jacket on the axis with E6000 glue works too. You need to make sure it remains straight, and that the glue does not touch the body of the motor (lest the motor gets clogged completely!). Allow 48h to dry and assemble it again. What a surprise, uh?

I will have to update the book in that chapter once I have the pictures that go with it. 

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Broken back piece vs integrated "flat" assembly battery part



As you know, we have two methods to repair the ubiquitous upper screw broken head support: the broken-back piece and the integral assembled "flat" piece.


If you have an original, working battery module, the only possible solution is to use the brokenback. Be sure of 1. putting a good deal of glue, and let it cure for at least 24h - 48 is better. And then, you will be able to assemble a number of times - but not many until it peels off again.

Now, if you can use the flat piece:


Then there is a much wider surface to adhere! it usually is a better solutiion. I'd first test it with the module in place but not glued, and pressing both calculator halves together with the batteries just to chekc it does work! Then you can adhere with E6000 glue, and wait 24 to 48 hours to cure.

Usually this is a better solution, since the piece holds better. I prefer it, but then I have more back in case something goes wrong. So far it has never happened.

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Zebra may go alone


We have received some inquiries on whether the zebra PCB assembled requires the zebra-holder. The zebra holder piece was designed to hold the separate zebras you can find in older calculators: the golde ones, not the elastomeric ones. If you find these, it is very likely your calculator won't work when reassembling - you'll have to replace it.

When you are using our zebra, it can very well go alone, without any support. It is strong enough to keep shape no matter what:


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Just learned that Systemyde will start another lot of HP41CL circuits. We already have two excellent calculators for conversion - and we will get others in time for end of January, which is the expected arrival time of the new circuits!


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new zebra PCB


When you are repairing full nut units, you may find different zebras, that may or many not be corroded. Here is a picture of the three different models of zebras, plus our own:


Today's message refers to the first set of zebras. On one side, they are the least common; on another, they have also the highest resistence, which is good enough for a calculator to work, but makes very difficult to operate peripherals - and in some cases virtually impossible - in particular the card reader - that power hog.

If your card reader seems anemic, this may be the reason. The second pair in principle should work - but I had unconsistent results with it. The third is the best of the originals, and works every time unless it is corroded or broken.

We have found that the replacement we have designed works every time. The connectors are exactly aligned with the upper and lower contacts, and there is no way it cant work unless corroded: no mobile parts, very solid and thick circuit paths, and there is no topological way for it to unfold after being put in the machine.

You can find it here:

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