HP Forum Archive 11

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NOT WORKING HP-41C Message #1 Posted by Jon on 23 Mar 2003, 5:07 p.m. I have an HP-41C (made in 1980) which was working perfect and suddenly it turned off by itself. Now I canīt turn it on. Somebody said me it could be static charge. I put the 4 batteries out and waited 24 hr, but it doesnīt work. Does anybody know what to do??? Thanks in advance Jon

Re: NOT WORKING HP-41C Message #2 Posted by Vieira, Luiz C. (Brazil) on 23 Mar 2003, 6:45 p.m., in response to message #1 by Jon Hello, Jon; based on a few experience dealling with HP41 (I have four working models with me) I'd tell you first: don't panic! Now let's see. Chances are you have a simple problem of bad connection (bad contact) between the BAT/IO assy (batteries and the I/O port connections and assembled in one single piece) and the keyboard. This is normally due to oxidation from battery leakage. You can check it by removing the batteries again and looking carefully at the batteries contacts. Can you see any green power that would smear in your fingers? This is the sort of oxidation that may form under the batteries' contacts. Sometimes you can see it, sometimes its hidden under the black plastic in the bottom of the batteries compartment that surrounds the BAT/IO assy contacts. Do you have the skills to open it and try to clean it? It seems to me yours is a fullnut. Please, check for it based on the image below. Let us know if you are willing to open it or not. Success. Luiz C. Vieira - Brazil

Re: NOT WORKING HP-41C Message #3 Posted by Jon on 24 Mar 2003, 1:49 a.m., in response to message #2 by Vieira, Luiz C. (Brazil) Thank you for your fast answer: It is a "fullnut". I have opened it (removing the four screws under the feet)and I canīt see any oxidation. It looks very clean. I have used a voltimeter and I read 6.2 V in the plastic connector. So it seems the battery contacts are ok. I canīt see any broken plastic in the screw holes (I donīt know the word in english) so I think it closes ok and the contact should be right.I havenīt dissasembled any more. After assembling again it doesnīt work. What else can I do?? Thanks again

Re: NOT WORKING HP-41C Message #4 Posted by Vieira, Luiz C. (Brazil) on 24 Mar 2003, 5:35 a.m., in response to message #3 by Jon Hi; please, downlaod this PDF file and check for the two first pictures showing the HP41 opened. There is a zebra connctor that allows the electrical connection between the "mainboard" and the keyboard. You should check this zebra connector carefully, because there is one type of them that has very thin golden-plated cooper trails. Also you should try to use plastic washers (thin ones) between the mainboard and the back cover to ensure there is preassure enough over the contacts. These are the most common problems and correcting procedures. I hope you have success. If not, post again. Best regards. Luiz C. Vieira - Brazil

Re: NOT WORKING HP-41C Message #5 Posted by John Flinn on 24 Mar 2003, 3:18 p.m., in response to message #4 by Vieira, Luiz C. (Brazil) Hi, Here is one more thing to check if your calculator doesn't turn on. If the coil springs in your battery pak are tired, sometimes there is not a good contact. Try stretching them a bit so that they give better pressure on the batteries. Another thing, if you take out the batteries for a couple of days, sometimes the calculator resets itself. I have a 41CX and I got it to work after removing a dead Advantage Pak module, stretching the coil springs and snugging up the tiny screws under the rubber foot pads. Hope this helps! John

Re: NOT WORKING HP-41C Message #6 Posted by Jon on 24 Mar 2003, 3:51 p.m., in response to message #4 by Vieira, Luiz C. (Brazil) I have dissasembled the main board and the zebra connector is clean. I have checked all the contacts and they are ok. In fact all the calculatorīs inside is perfect (clean, without any corrosion). And after assembling everything again I have found out the problem: battery contacts donīt work properly. The previous owner painted them with silver paint (conductive). It has very good aspect but it seems to lose conductivity due to batteries friction. I have a photo but I donīt know how to attach it If I place silver paper in each battery contact the calculator works again Now I know the problem but not the best solution. Does anybody have experience solving this failure. Thanks in advance Jon

Re: NOT WORKING HP-41C Message #7 Posted by Vieira, Luiz C. (Brazil) on 24 Mar 2003, 3:59 p.m., in response to message #6 by Jon Hi; there are self-adhesive cooper foil from Chomerics (it seems to me the e-address is www.chomerics.com) and I think they're the best solution. It is not golden plated, but it has conductive glue and you can cut it and apply directly over the battery contacts.If you look carefully, there is some part of the contactcs in the calculator's BATT/IO assy that are exposed, so you can even solder the foil (low-temperature soldering iron). At the Chomerics site you may request a sampla, that will be enough for your needs. Best ergards and success. Luiz C. Vieira - Brazil

Re: NOT WORKING HP-41C Message #8 Posted by David Smith on 24 Mar 2003, 4:21 p.m., in response to message #6 by Jon You can try more silver paint. I don't know if you can still solder to the contacts, but if so I use small pieces or brass "U" channel strip available at most hobby shops. Cut a small piece of the brass strip a little shorter than the battery contact. Clean and sand lightly inside the brass piece. I run a small bead of solder on the battery contact, a small bead inside the brass channel, place the brass over the battery contact, heat from the top to melt the two solder beads together. Voila, a very heavy duty battery contact.

Re: NOT WORKING HP-41C Message #9 Posted by Jon on 25 Mar 2003, 10:14 a.m., in response to message #8 by David Smith Thank you to everybody: I will try first the self adhesive copper foil. But it is interesting to know that I can even solder it. Thanks again Jon

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