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!