Musings and comments about our common interest
I have now an old HP41c where the upper circuit is pressed down to the zebra connectors via nuts. Now, it is difficult to ensure an even pressure and I am having problems with some of the digits. But if we force the nuts, I may break the post - as it has happened in other cases. These are the situations our new piece (wait until we can put it on sale) is made for.
This piece is intended to be put on the lower posts (where it fits tight to aid in case of cracked posts) and gives the necessary mm. of thickness so that the back side of the original type can pass the pressure on the circuit so that it stands firm on the zebra connectors. This negates the use of nuts, which can be changed only a couple of times, lest they break the thread of the post (or the post directly, as it has happened to me a couple of times). I am testing different thicknesses to find which will be the final product.
Say goodbye to the nuts!
We have now prepared a couple of new products designed to solve more HP41CL repair problems. We will discuss today the first one.
Our bent to do c to CL conversions has led us to specialize on full nut repair, instead of half nuts. But some of the tools and methods are also valuable for half nuts too!
The first of the new items we have created is the adaptor to replace screwed nuts in the original HP41C. You may have seen one of this: the processor circuit is secured to the main board with metal nuts around the lower screw posts. The problem with these: it is very easy to destroy the thread, since he read was formed by the action of the nut on the first attachment, nearly 40 years ago!
In the later units, the processor was secured in place by the pressure of the back side through two cylinders collated to the case. If you have one of the old cases, and you have broken the nut thread, you need to find a solution to push the circuit down against the zebra connectors. This is such solution.
We have created a nylon piece that fits tightly around the lower screw posts, with a small bezel to ease the port entrance, and occasionally making a broken post able again. This piece translates the pressure from the back side of the calculator down to the circuit. Don't need to find the right height, or to adjust the angle: it will work - every time.
The piece has sides! As the back side has an angle compared with the circuit surface, we needed to create this angle to the piece. Therefore it can only be put one way.
As the color here really doesn't matter, we have created the price in the cheapest, clearest color from 3D printing: white.
I hope that is piece helps some of you fixing your beloved calculator!
While waiting for the side cover 3D model with a new texture, we have received the samples of another HP41c repair item that has given us a lot of headaches: the zebra connector between the full-nut circuit and the main body. As in many of this things, it is due to the effort of Ignacio Sánchez to find a proper supplier in China. We have received the first shipment and he will throughly test it with a difficult HP41cv. We will report on the results and put it on sale for you DIYers!
The zebra connector has two different models: the initial one, where both sides were united by a plastic membrane, and had good repairability if it wasn't corroded, and the newer "white-green" gummy-like connector. Once it was detached from the circuit, this latter usually didn't work again. This is the one we're aiming to replace.
Stay tuned for news about the first repairs performed with it! We'll post the results here and in hpmuseum.org.
Most of the HP41c that we receive for conversion are missing the side cover. You can find in ebay side covers but as they are from overseas, they are quite expensive for us Europeans. And you can find some in 3D printing sites, but neither the material quality nor the design makes for a good replacement. So based in our experience with the battery-port assembly 3D printing and with a couple of new materials, we think we may get it right!
Here you can see a rendering of the peice we have designed. We have tried slightly thicker arms, since this is the breaking point, but not too much. We have ordered the first set of samples and we are eager to show you how it looks like in reality!
Let's start with the simplest financial calculator from HP. There has been a 10b calculator from a long ago, but the current model is much, much better than the previous versions.
From the innards: this calculator is using the same processor as other fast units like the new 12c. A completely new job by the techs in the HP calculator department.
Also, it has much more functions than the previous versions: a lot of mathematical functions (including trigonometrics and hyperbolics, in a financial calculator) and many financial, including break even analysis.
The body and keyboard is much better than the competition - the keyboard in particular ranks there with the best, and clearly better than the HP50g or HP30b.
At the price (slightly below 30 EUR) is a steal, and a much better buy than any of the 12C or 17BII units.
The only thing that puts it down for me is the lack of RPN entry method, and the lack of programmability. If you don't need any of these, then it may be your unit!
Many of us are working in financial positions. I have seen in many offices financial personnel using what in calculator business are called "four banger": just the basic four and typically percentages. In some cases they also have a small printer. This is more than enough in most cases. And in the cases this is not required, you use the Excel spreadsheet - which can also show in a presentable way the results that you are looking for.
The financial calculators are now used in more informal situations: meetings, discussions, workgroups, etc. In that setting, there is still a need for a financial calculator.
We currently sell the follwing financial calculators:
In addition, we typically have the oder HP17BII units from the Pioneer series: a different feeling and a still very valid calculator.
Tomorrow we will describe the different units
Some of you guys have several calculators to repair and have asked for a better price if you buy more units. Also we wanted a more convenient way of selling and producing these parts. So we decided to join them and sell them together. You can then cut them by the crosses and use them as individual pieces. Exact length of the cross is not critical.
Just wanted to tell you guys that I have fixed the article Battery-port assembly. Apparently it was configured with options, but no option was activated and it couldn't be bought!
You can find it here :Módulo conector de baterías y puertos de expansión de las HP-41c/cv/cx
Sorry for the inconveniences of those who wanted to buy it!!
A short one (very far from the long posts involving repairing manuals):
One of my sons is learning to do divisions, and he has to practice. So I took the HP41CL to generate random divisions. I always have among the modules virtually plugged in the system Sandmath 4x4, which has the function RND (I think it is there - the only thing for sure is that having only the advantage pack and Sandmath, it DOES work), so I made this short program in all of 1 minute, plus other 15 seconds to assign it to a key:
1 LBL RAND
It stores a 5 digit number in X and a 2 digit in Y. My son can execute it and press x<>y in order to get the divisor too.
There is no way I could get a faster solution with a computer or any other more modern calculator!!
Disclaimer: this is a manual for the exchange of the battery-port assembly. It doesn’t pretend to be a full repair guide. There may be many failure modes in a HP41, and to diagnose even the most frequent of them is beyond the scope of this manual.
We assume that the machine doesn’t work because of the rust in the battery assembly, but it may be due to many other things:
- broken screw posts
- broken upper screw supports.
- rust in the main circuit
1. Do you have a) a readymade assembly or b) the piece and the flex circuit, and you need to put it together? If a), keep on reading; if b), go first to the manual for the flex-pcb.
2. Remove the battery pack and disassemble the calculator. With a flat screwdriver, pry in-between the body and the rubber supports. Be careful because below the rubber there is an adhesive band, and we want it to come up together with the rubber, to be able to use it thereafter. Also, we want to avoid damage to it. Put them away on top of a paper. If they are around your work area, they will be a pain since they adhere to everything!
3. With a Philips screwdriver, unscrew the 4 screws. Do not exert too much force - the holes are not screwed internally, and pushing it too hard will break the inner surface, rendering it “unscrewable” henceforth.
4. Pull the back side of the calculator upwards. and leave it upwards beside the calculator. Look inside: in the interior is green, with an integrated circuit in the middle, you have a “half-nut” calculator; if you see a whitish keyboard circuit and another circuit on top of it, you have a “full-nut”. The full nut upper circuit may be screwed to the screw posts with a nut, or held in place by means of pressure of the case (in this case (no pun intended) there are two cylinders protruding down from the case with the task of applying that pressure.
Take out the black plastic that covers the circuit.
Now, take the time to observe:
- Are the screw posts broken? look into the upper and lower screw posts. It may happen that they aren to completely broken, but there are cases in which there are close to invisible cracks, that may lead to the system not working.
- Is there green rust in the circuit? if so, you will have to clean it. In our experience, there is nothing better than Caig De-Oxit D5. You have to apply it and rub it with a cotton stick. You will be surprised about how well it removes the green part. If you have a full nut, you will have to lift the upper circuit, in order to clean below it as well. Do it until all green has been completely removed. In some cases, it was so corroded that a circuit piste disappears. There are silver conductive pens that will allow you to “draw” the piste again.
- In the back case, are the upper screw head supports broken or cracked? If so, the best solution we have found is to remove the support altogether and use our brokenback repair piece.
5. Pull up the original battery-port assembly. It is removed by just pulling it up, vertically (this is important). It is not glued in place, and it should come up. Increase force carefully, and do not move it horizontally, since you will break the vertical table that hold it in place.
6. Clean everything below it. Usually it ends up full of grease - I don’t know where it comes from!. Pass Caig Deoxit through all contacts in view in the main circuit.
7. Place the new assembly on the back case, making sure the tabs in the case enter in the holes. It fits tight but comfortably.
8. Replace the black plastic. In a full-nut, you will have to pull up the processor circuit.
9. Put the back case in place. Be sure of placing the intermediate plastic piece (the one that covers 3 sides of the calculator) the right way: with the calculator upside-down, the angle of the piece seen from the port side should be like this: \ /.
10. Screw back the screws. I usually start with the upper screws, but I don’t think it is critical. What is important is to do it tightly, but not forcing it too much since you can break the 30-year old posts. And you are now done!