Musings and comments about our common interest
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!
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!!
Instructions for use of back side repair piece.
1. Be aware, before everything else, that the piece has a right side and a left side. This is due to the space for the tabs in the calculator that keep the battery-port assembly in place. You need to be aware of this at all times - more so if you want to cut it as explained below.
2. Decide whether you will replace both sides or just one. The decision is easy when both are broken, but if one is not, you'll have to check whether the old standing support will withstand the pressure for long. Our recommendation is to replace both sides. If later one of the sides breaks down, the repair will be much more difficult and probably less solid. And you have already paid for both sides!!
3. If you are going to replace just one side, cut with a hobbyist scissors just the side you don't need, according to picture enclosed, again, be careful of cutting the side you dont need, since the piece has a single correct orientation!. The rest of the piece will serve to increment the glued area, better align the piece in place and also to better support the battery-port assembly.
2. With a Dremel machine, file and level the area that had the support. You don't need to remove the tabs in between the two screw post, but you need to remove them if they are twisted or half-broken.
5. Put the piece in place. There is only one "right" way. The cross part is tight because it is needed to properly locate both holes at the extremes. Do not force it. Please make sure it is not bent downwards. Make sure it makes good contact. Remove the piece.
6. Put some glue in the bottom of the piece. Do not put too much or it will go out when pressed. We have used E6000 black glue with good results. Do not use cyanoacrylate glues. Put the piece back in place. Press and remove with a stick or a blade the excess glue, if any. If the screw holes are partially obstructed by glue, pass a screw in the opposite direction (to avoid separating the piece from the back side).
7. Secure the piece in place with a pair of clamps - lighter pressure like clothes' pegs will not be enough. Be careful that there is no excess glue from the other side of the case and the clamps are adhered to the piece! Leave for 24h for the glue to cure. And you're done! You have a repaired back that will withstand a lot of abuse again.
8. The piece is designed to accept both the original and the new battery-ports assembly - so you need to press it down to have it in place. The screw holes should fit a little bit tighter than in the original calculator, but should be perfectly aligned with the assemblies and the screw posts below.
Also, if you're buying from the US, it is maybe better to buy it directly from Shapeways there (just click on the link)
1. The battery-ports assembly includes the base piece and a flex circuit expertly adhered by our expert. According to him, the adherence over the nylon material used in thos piece seems to be better than on the original's material!
2. You can order the nylon piece alone at the price of 26 € each plus postage (while the finished piece includes shipment too within Europe), but then you'll have to paste yourself. My experience tells me that it is worth to leave it to the experts!
3. The battery-ports assembly fits tighter than the original piece. This is made on purpose: we have seen some instability on original pieces, so much so that it is predicated to assemble the calculator with the port covers in to make sure that the assembly doesn't move. This is not the case with the new piece.
4. The small piece used to repair the upper screw supports fits perfectly under the repair piece - it is DESIGNED to be like that. The gaps and the slots it has fit perfectly into both the original and the new assemblies. In fact, it was designed to improve it support in case the original calculator small stands are damaged
More questions? please ask to firstname.lastname@example.org
If you have bought a HP41C, chances are that you have found a machine that has a broken back half. Typically, this happens when the top screw supports break under the tension required to bring together the two halves, putting presure on the foam under the flex circuit. A strong pressure is required for the calculator to work properly, as all of us that have assembled calculators remember.
The problem when repairing the broken supports is that it is very difficult to paste again the broken pieces - and when you do it, they tend to break easily. When you see a completely broken post, it is easy to see that the adherence area is very small. So we decided to find a solution. We designed a piece that can be adhered over a wider surface, that can be used for both sides or one side, and that can integrate woth the original battery-port assembly or with our new 3D-printed model.
This is how a partial repair looks like: first we cut the part we need:
Then, we need to remove all rests of the original screw support with a Dremel machine or similar. Then, we put the part in place. The way it is designed, it can only be put on way and it also serves to keep it in place. Then, we paste it and keep together with a clothes peg or similar overnight. And this how it looks with the repaired piece:
The part will fit under the battery connector module. Also, the way it is designed, it helps to keep a strong connection between the module and the circuit, even if for some reason the glue doesn't hold.
One of the common problems that plague old HP41c is the breaking of the upper screw supports in the back side of the calculator. The lack of pressure thus causes the battery circuit to not make full contact - and the calculator doesn't work. The repair is quite difficult, since the contact area for adhering the broken plastic is very limited. We have created a piece that fits below the battery contact assemble, has enough surface to adhere to the back side, and can even substitute for the broken stands that fix the battery contact assembly:
You can remove the rests of the two screw supports of the case and glue this piece in place. If one support remains in place, you can cut the piece in half and just glue one part of the piece. Then you can put the battery assembly (original or new) on top of it, guided by the elevated parts, since it it designed to fit as below:
We will now work on the process: find the right glue, how to remove the rest of the screw stands, etc., so it is not ready for ordering yet. Please email to email@example.com if you're interested on repairing your back-side with this piece. In any case, it is a good item for your repair box!
Continuing with the repair thread we initiated 3 issues of this blog ago, we go now into the adhesive conductive tape. This is the description I get from the 3M page:
3MTM Electrically Conductive Aluminum Tape 3302 is a 2.0 mil (50 micron) high strength dead soft aluminum foil coated with specially formulated conductive pressure sensitive acrylic adhesive system. Good adhesion, malleability and adhesive conductivity allow for extremely low resistance and make this an excellent shielding tape. Designed to meet a wide variety of EMI and RFI shielding applications in the electronics industry. Also for use in printed circuit manufacture and repair.
Cut in small pieces, it can be used to cover the eroded parts of the battery contacts. Please remember to remove all oxide with Caig De-Oxit first; in some cases, the conductive film of the circuit will be destroyed in the contacting part, and there comes handy the conductive aluminium tape. You need to cover the whole contact, to maximize the electrical transfer area. Nacho thinks that it also needs to look good: a proper repairer will cover all four contacts, so that it looks coherent and symmetrical.
It also can be used in other circuits to create aground plane, and also for shielding. Every repairer should have this in his toolbox.
The assembled repair kit is a drop-in part for damaged-corroded battery contacts in the hp41c family of advanced scientific calculators. It solves the main issue that plagues old 41c units.
There is a cheap alternative when the damage is minimal. There are times when there is not too much corrosion, or where friction has caused the black support to appear (meaning the metal has disappeared in the contact area, but it is still available around). In these cases, there are two material that you need to know: Caig De-Oxit and the adhesive Aluminium paper.
Caig is an American company that produces several liquids to clean metals. I have been using its compounds for my hi-fi hobby for a long time - the sound and image really improve when you clean the interconnect contacts with De-Oxit; and they are maintained in good condition (and the golden or nickeled contacts preserved from dendritic corrosion) with Caig Pro-Gold.
Well, Caig De-Oxit works magic for removing corrosion. Use it with cotton sticks, rub them gently on the corroded part and you will see how the corrosion dissolves.
I have been using it recently on several deep corrosion cases on hp41c. Not only the battery assembly was corroded beyond repair, but also the circuit lines were completely green. As the battery assembly circuit had been destroyed by corrosion, the only solution there was the repair kit; but for the main calculator circuit, a generous application of De-Oxit led to a completely clean machine that worked from the first second it was reconnected. I must say that I have also failed with other calculators, but that may be due to additional damage elsewhere.
Tomorrow I will show to you the adhesive conductive film
I had not realized that the stock level for HP41c repair kit was at zero again! But we have reordered and we have again 12 units in stock.
As there were a lot of problems with the transport methods for this product, we have decided to have it included in the price. Therefore, from now on shipping is included in the price, and there are no more hassles when the system proposes an expensive shipping method (while it could always be changed to registered letter, once the user had logged in)
Good luck with your HP41c repairs!
Here are some tips in order to have a lasting, quality battery bay repair: