Hp 41CX only displays something when pressed on

[Lode]

Hi,

I got an HP 41CX which appears as if it doesn't turn on, but it briefly works when firmly pressing downwards on it (when it's horizontal on a table).

This works the best when it's pressed at the bottom side of it, and less well when pressed on the display side.

It seems like a display problem, because when entering some number while it doesn't display anything, then pressing it, it shows the number entered earlier. In fact it even works when pressing the left and right bottom sides downwards gently at the same time.

Dear experts, any clues what could be wrong with it, and if there could be a safe way to repair it? I don't think it has ever been opened...

Thanks

[AndiGer]

Sounds like broken posts. Guess it's a fullnut - square corners display ...

[Lode]

Yes indeed it is. In that case, I think I know where to look: this guide https://www.hpmuseum.org/cgi-sys/cgiwrap...cgi?read=2

Thanks!

[Lode]

Hi,

Unfortunately it's not going too well with this.

I opened it up, and saw that there is 1 broken post: the right one on this picture:

https://i.imgur.com/RkFKnN3.png

That post is not just cracked in 2 halves, but also loose from the bottom:

https://i.imgur.com/C0geMHV.png

But things are even worse now! By opening/closing the calculator multiple times, other things start breaking, namely these two plastic things for the battery contacts...

https://i.imgur.com/MndMV1P.png

Also, before it used to operate normally when pressing the bottom, but now it was behaving very strangely, first it said memory lost, then after pressing alpha displayed this weird thing. What is it doing here???

https://i.imgur.com/WBKdwrp.png

That was the last thing it displayed. Ever since the battery contact fell out (with those new two plastic things broken shown above) and I try to reassemble it and push the sides hard, nothing gets displayed or nothing beeps anymore at all

Basically, it's all brittle plastics and sensitive contacts galore! Anyone know any more stable ways to fix this? Anything that can be 3D printed? Or alternative ways of making good contacts? Do you think this one can be saved at all?

P.S. I also don't really know how to properly get materials like those particular exact types of screws but longer (in Europe)

Thanks!

EDIT: after another reopening/reclosing it can display things again (still only when pressing the bottom), but it's permanently stuck in USER mode, and the user key does not toggle it off. Even when removing and reinserting the batteries it keeps doing that. Could some of the top buttons be breaking too? Or is there some feature going on here that I don't know about, and it ended up randomly in this state when the weird stuff from the last screenshot above happened?

EDIT2: it actually seems to keep remembering numbers for a very long time after removing the batteries. Is a capacitor holding some power to retain memory? Any ideas how long it can keep memory without batteries?

EDIT3: backspace+on cleared that memory and now it behaves normal again so that's solved (other than that the bottom contacts still require pressing on it so I still need to succeed in that whole gluing thing...), but the user button still doesn't do anything, now user is permanently off. Could that one button also have a bad contact?

[hth]

Some people probably have a lot more information with this than me, but I will chime in anyway with some random information that hopefully will cheer you up a little bit.

First of all, there was a post back where someone replaced the bottom screw posts completely. I think using some metal piece and gluing it in. I could be wrong, my memory is fuzzy. It think metal/machine screws were used on those. So that should be fixable. (I do not have a link to that post at hand, sorry about that.)

The plastic on the HP-41 can be welded as it seems to be styrene. You can use the same way plastic modellers use, a liquid solvent. Basically you take some on a small brush, apply in the crack/gap and let it seep in using capillary action, wait 3-4 seconds (any excess will evaporate, but the liquid in the gap stays, softening the edges), then press together and hold (the longer the better). It works best if you can use some means of maintaining pressure on it for quite a while. A weld like this, if done in a perfect way is just as strong as the plastic itself. You need to put the pieces back to where they used to be (to get the best fit). I fixed the upper screw hills this way on mine (the ones next to your broken battery contacts) this way. I am not sure how fixable your parts actually are in practise, as the area to glue is so small and it is probably hard to put proper pressure on it too. Is it really needed? I had some small piece coming off mine around that area and it seemed to work fine without it. Maybe I glued in the thing it was supposed to position, I cannot remember and I am not going to open it to check...

If I remember correctly I welded one of the lower screw posts on mine, which was cracked by letting the solvent seep into the crack and then used a tweezer/clamp to press it together while it set. Then I used one of the screws Monte offers in the repair kit sold with the 41CL.

I had a plain 41C that was left without batteries for a week and it retained the memory when the battery was put back in. Other models with more RAM (and possibly timer chip) may not last that long. The timer chip seems to take every excuse it can find to reset itself, while RAM is less sensitive.

If you cannot make USER key work, a work around is manipulate flag 27 (CF and SF). At least that makes it possible to enter and leave user mode.

You will need to make the screws hold it together, otherwise it will not function properly. Monte mentioned that he uses rubber bands as a temporary means to hold it together for testing.

[brierand]

(10-21-2019 07:47 PM)Lode Wrote:  Hi,

I got an HP 41CX which appears as if it doesn't turn on, but it briefly works when firmly pressing downwards on it (when it's horizontal on a table).

This works the best when it's pressed at the bottom side of it, and less well when pressed on the display side.

It seems like a display problem, because when entering some number while it doesn't display anything, then pressing it, it shows the number entered earlier. In fact it even works when pressing the left and right bottom sides downwards gently at the same time.

Dear experts, any clues what could be wrong with it, and if there could be a safe way to repair it? I don't think it has ever been opened...

Thanks

Before opening your calculator, read the following:
https://www.hpmuseum.org/cgi-sys/cgiwrap...i?read=149
It saved an HP41CX I had just bought one day!

[ijabbott]

thecalculatorstore.com seems to stock lots of parts for repairing HP 41C series calculators.

[Jose Gonzalez Divasson]

We have found that gluing this piece works well. It substitutes the lower posts and can handle the zebras too:

http://www.thecalculatorstore.com/Lower-Post-Repair-par



It works with the same screws.