Problems with HP41C



#4

Hello everyone,

I recently got an HP41C from my brother who hasn't used it anymore sincefor more than 10 years. There were no batteries inside anymore, but there was a little greenish color on the battery contacts. I tried with batteries from my 41CV- but the C didn't wake up. So i decided to open it and polish the battery contacts and the contacts between the upper and bottom part of the calculator (which were also a little green). After cleaning, all contacts were bright yellow (OK i thought), but after reassembling and testing with good batteries, it did not wake up...

What could i do next? Is there some testing procedure possible to find the cause? (unfortunately i am not an electrical engineer and i do not have testing equipment besides a multimeter)

I would be very happy to bring this machine back to life because it is a beautiful oldie, with the "steep" buttons! (S/N 2026A01398)
Thanks for any hints,
Hugo


#5

Hi Hugo,


Yes, contact oxydation are a pain. Most probably your zebra connectors are also oxydated - you will need to open your calc and clean this up.


#6

Hello Thibaut,

i suppose you mean with the zebra connectors the ones between the under- and upper part of the calculator? These i have already cleaned- are there other sensitive connectors?

Hugo


#7

Did you try the battery holder from the good calculator. The spring in the holder could be corroded too.

#8

If your 41C is a fullnut (no rounded edges around the display - see the HP41 pictures in the museum), it has a second connector that could have failed. It's underneath the main electronics board. To get to it, you have to losen the two nuts that hold the board down. These also provide the pressure necessary to ensure contact between the electronics board and the keyboard.

Two things could cause problems there: Corrosion or cracked screw posts. You can always try to remove corrosion if that's the problem, and there are several sources of information on how to repair cracked screw posts. I don't know about halfnuts - I have never opened one so far. I think they, too, can corrode, but the screw posts are no longer critical to the conection. Would make it a bit easier, then...

The problem is that these posts are extremely fragile and are easily damaged just by unscrewing the nuts. Therefore, I would first try again to fix the contact you already cleaned, between the battery/port assembly and the keyboard. Clean it again very carefully using very fine (1000 grit) sandpaper, then apply a contact spray to both the board and the felx circuit. Repeat if necessary. Hold the two halves togehter without inserting the screws and see if you can get the machine to life. Sometimes pressing on one side or the other or slightly moving the top half against the bottom suddenly produces a sign of life.

You should only dissassemble the lower contact if all of the above doesn't lead anywhere. And of course, make sure the problem is not the batteries ;-)

Tell me if this helps.
Cheers,
Victor

#9

Hello, Hugo;

Please, look at the pictures below (they are composed with some layers, that's why there are borders around mixed parts, O.K.?)

This is what you see whn you open the calculator and remove the battery contacts assy (black protective plastic sheet is not shown)


If you (carefuly) remove the mainboard, you'll see that there is a connector made with a lot of golden-plated wires. There's a chance you'll need to CAREFULY clean both the connector itself and the pads under the mainboard.

You should also remove the connector and clean the keyboard connecting pads.

Chances are you have cracked or broken screw posts. If the srews are not tighten (not too much), only enough to achieve the contact between the mainboard and the battery assy with the keyboard, the "power supply" from batteries will not reach the mainboard's contacts. Also, if the mainboard cannot communicate with the LCD, no "image" will come from it.

If you need more advice (say, about broken posts), let us know.

Success.

Luiz (Brazil)


#10

Hi Hugo, Thibaut, Chan Tran, folks;

I was setting images up and I took too long to post. Now I see Hugo have already done what he was supposed to. The images are no longer needed, though.

Hugo, if the calculator still does not swithc to ON as there is nothing in the LCD, try [SHIFT][BEEP] to confirm it's not ON indeed; maybe you have it working and there are problems in the LCD.

Some newer minboards need thin plastic washers to increase pressure in the small mainboard so it firmly connects with the keyboard. If you have the means to enhance this pressure, it would worth trying.

Success.

Luiz (Brazil)

#11

Hi Thibaut, Chan,Victor and Luiz,

thanks all for the good advice, i will need some time to try it all out! i will post a message again when i am through the list...

Of the items mentiones: i do not have broken screw posts (all four screws work OK) but perhaps the connectors are not yet clean enough. The beep i already tested: no sound- so it is not only the display that does not work. The 41C i have is one without rounded corners so i will have to check that second connector also.

To test the C, i used my batteries and the battery case of my 41CV (that works with the card reader- so the batteries will be OK). But i have noticed that when i take the batteries out of the CV and leave them out a while, this calculator also has difficulties to start up. I have to remove all modules and the card reader, reinsert the battery pack to get it working again. Perhaps also a sign of corrosion somewhere? And when it starts up, sometimes i have a MEMORY LOST.

Anyways thanks already for all advice! Hugo


#12

Hugo,


As we live in the same country I could have a look and try my luck on your calculator... drop me an e-mail (I live around Brussels) if you want to arrange a meeting.

Best regards,

Thibaut

#13

Hugo:

You should also try to look for broken battery contacts. Sometimes they look nice but are broken in the middle (where the battery is in contact). It is very easy to check it. Just place a piece of aluminum paper in each contact. You must guarantee there is contact in the borders, not just in the middle. I have found that problem in 2 of 4 HP-41C, Cv,Cx that I have repaired.
If that´s the problem make us know. It isn´t so hard to repair.

Jon

#14

Hi all,

I cleaned all contacts again, including the one between the PCB's inside. After reassembling, it works again!

Although i do not exactly know which contact has posed the problem, i am vary happy to see this 41C alive again.

Thanks for all good advice! To my opinion, this is not just a forum, it is a quick and very efficient HP helpdesk!!

Best regards,
Hugo


#15

Congratulations, Hugo, on your successful repair. I know how it feels: I just repaired a defective HP 41C myself in much the same manner. These machines are soooo beautiful...

Cheers,
Victor

#16

Congrats and thank you, Hugo! 8^)))))

thank you for sharing the success, too.

Best regards.

Luiz (Brazil)


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