HP41-CX Repair of broken posts with photos

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HP41-CX Repair of broken posts with photos

Postby Drulli » Thu Mar 20, 2014 9:02 pm

Hi all,
my beloved HP-41CX is broken. Its a coconut version, produced 1984.
After years I wanted to start it again, but even with new batteries the hp was dead.
Even worse I noticed, that when pulling the Card Reader out, I can open the covers at the top.

Thus I need to open it to find the reason, if possible.
The biggest problem was to find the screws. Yes, they are behind the rubber feet, but when I removed them, no screw was visible. Finally I found out that between the rubber feet and the chassis there is a thin foil which needs to be removed as well. :mrgreen:

Very soon it became clear that the screw poles at the top and one at the bottom of the calculator were broken.

According to a very good repair instruction I am now trying to fix it.
http://www.hpmuseum.org/cgi-sys/cgiwrap/hpmuseum/articles.cgi?read=2

During my research in web I noticed that photos showing broken screw post and other details are very rare. Photos would have been helpful to get a better understanding of the problem. Thus I made some photos and put them on my homepage. (Photos are made with my mobile Nokia Lumia 620).
http://www.schwalvenberg.com/en/hp-41cx/104-step-1-disassembling

I will add more photos when I have put the hp-41 together again.
Cross fingers!
Last edited by Drulli on Sat Apr 30, 2016 11:04 am, edited 4 times in total.
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Re: HP41-CX Repair of broken posts with photos

Postby Drulli » Mon Mar 31, 2014 9:04 pm

Hi all,
I managed to rebuild the poles, even though It was not simple at all. Main challenge was to rebuild the pole in the bottom in a real vertical Position. Furthermore rest of the Cyanacrylat adhesive Need to be removed when it became solid (rasp).
When I put the CX together the disappointment was big when nothing happened. But at least I could hear the processor working, but pressing ON, USER, ALPFH had no effect.
Only once I was able to create a single beep.
I opend the CX again an checked the voltages the Display connections. All fine.

But one capacitor look strange - the bottom Color was not plain white anymore, there is some brown colors as well, and the bottom was not really flat, it was a bit dented. When I measured the resistance it was 0, strange.
Finally I bend it up and oops, it was blasted.

I stored 2 pics on my Homepage. http://www.schwalvenberg.com/en/hp-41cx/105-step-3-blasted-inductor
Unfortunately on this capacitor there is nothing written on.
Does anybody knows where I can find the specification for that element?
What is its size (µF), what else to know in order to replace it?
Thanks!
Last edited by Drulli on Sat Apr 30, 2016 11:06 am, edited 2 times in total.
Drulli
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Re: HP41-CX Repair of broken posts with photos

Postby Garth » Mon Mar 31, 2014 9:47 pm

It looks like it might be a battery of some sort, like to preserve the memory while the normal batteries are changed. Can you see what part of the circuit it goes to, like from the memories' power to ground? If that's what it is, almost any capacitor that will fit will probably do (as long as its WVDC is at least 6.3V), and you might be able to find supercaps in that size. The more capacitance, the better, as long as the voltage requirement is met. There might also be a lithium or other battery that would work there, but I don't have enough info to say with any certainty.
http://WilsonMinesCo.com (60 HP-41 links on the links page)
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Re: HP41-CX Repair of broken posts with photos

Postby Garth » Mon Mar 31, 2014 9:50 pm

On second look, another possibility is that it's an inductor, and in that case it makes sense that you measure zero ohms. I can't think of anything there that would need an inductor though, like for a power supply voltage converter. Is there any possibility that the burned area could be from something external to this part?
http://WilsonMinesCo.com (60 HP-41 links on the links page)
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Re: HP41-CX Repair of broken posts with photos

Postby Drulli » Tue Apr 01, 2014 8:40 pm

Hello Garth,
meanwhile I took another picture of the suspicious component, and surprise, surprise, it looks like an inductor.
http://www.schwalvenberg.com/en/hp-41cx/105-step-3-blasted-inductor
Its connected to 2 diodes, if I am right.
Is that part of the memory function? I would bet on power conversion or similar. :?:

So, if the resistance is 0 Ohm, it is not sure if it is broken. Maybe only the grey coat cracked. It could be caused by a soldering point the inductor probably was pressed against.

Anyhow, now I have no clue which replacement component I should take. And if is still working properly despite its blasted appearance, what else might be the reason that the processer is really dead now.

Soldering on the board is not that easy due to its doubled layer. :?
Have you ever seen a board layout, or a list of components with its specifications?
I need more information...
Last edited by Drulli on Sat Apr 30, 2016 11:06 am, edited 1 time in total.
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Re: HP41-CX Repair of broken posts with photos

Postby Garth » Tue Apr 01, 2014 10:30 pm

It does look like it's ok as an inductor, and if it has diodes connected to it in the circuit, it sounds like there is some voltage conversion going on. I don't know what to suggest other than to look in the pages linked in the HP-41 section of the links page on my website, at http://wilsonminesco.com/links.html#hp41 . If you can't figure it out, there are two repair services there, done by men who are there because they really do love the 41 and are not there for a quick buck. I know one of them quit taking new jobs for a while because he got behind and had some health problems, but the other is open for normal business AFAIK.
http://WilsonMinesCo.com (60 HP-41 links on the links page)
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Re: HP41-CX Repair of broken posts with photos

Postby Drulli » Sat Apr 05, 2014 9:47 am

Hi all,
I am looking for the HP-41CX Service Manual and if possible a schematic drawing of the HP-41CX model.
The service manual must be available still.
http://www.hpmuseum.org/cgi-sys/cgiwrap ... ead=167546

I have the found the HP-41C Service Manual.

Any hint from anyone how I can get this doc?
Drulli
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Re: HP41-CX Repair of broken posts with photos

Postby Garth » Sat Apr 05, 2014 10:37 am

See if these help. They're from my links page. Unfortunately it looks like another one I had which should be best just gives a 404 now.
http://www.keesvandersanden.nl/calculat ... ullnut.php
http://s839.photobucket.com/albums/zz31 ... /HP41_LCD/
http://www.clonix41.org/Maintenance/IO_ ... _Block.htm
http://WilsonMinesCo.com (60 HP-41 links on the links page)
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Re: HP41-CX Repair of broken posts with photos

Postby Drulli » Sat Apr 05, 2014 8:22 pm

Hi Garth,
Today I got hands on the HP-41CX Service Manual and could identify the component.
Its the L2 inductor, toroidal, 1mH.
(its on every board, location and type depending on the model)

Thus its ok if its 0 Ohm, as long its working still like an inductor naturally.
I placed a picture of the HP-41C/CV/CV Common Board Component Location Diagram on the above mentioned url.

Next step: checking the remaining components.
Drulli
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Re: HP41-CX Repair of broken posts with photos

Postby Drulli » Sun Apr 06, 2014 10:24 am

Hello Garth,
Today I checked again the components on the CPU board with the help of the HP-41C/CV/CV Common Board Component Location Diagram and the schematics. Everything was still fine, diodes behave as diodes, resistors showed the right level of resistance and capacitors seem to work as well.

For avoidance of connection problems I cleaned all connectors on the keyboard and CPU board. I once again rasp final tenth of millimeter away of the broken and now reconstructed bottom post.
GND and BAT + connection from keyboard was ok. So, I pulled my HP-41CX together and the brave companion woke up informing me about:

MEMORY LOST

What a great feeling! I checked about its ON reliability and it looks stable. Mathematic Module - OK.The card Reader I checked as well, I inserted a cleaning card and to my disappointment, the cards was sucked in but got stuck in the middle in some king of glue, that even stick on the card when I pulled it back. The CX was not amused about that kind of input and woke up with Memory Lost. Otherwise still everything is fine. I will now check how to repair the card reader. :D

Thanks Garth for your support during this "project".
Drulli
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