HP Forum Archive 06

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HP-41C flex circuit problems Message #1 Posted by Brian on 30 Sept 2001, 7:44 p.m. On my 17 yr old CX, the flex circuit which makes up the battery contacts and module port contacts had problems at the area that makes contact with the main circuit board. If I plugged in a module or a blank port cover in port 2 or 4 the calculator display would go blank or display garbage when some keys were pressed. The rubber under the flex had deteriorated and lost its stiffness. Instead of replacing the rubber strip, which would require removing the flex circuit, I inserted a couple small thin cable ties between the flex circuit and the rubber strip. It was difficult to insert the cable ties between the rubber strip and the flex circuit since the rubber had melted onto the flex circuit. It took some work to loosen the rubber from the flex. This fix may not last very long.

Re: HP-41C flex circuit problems Message #2 Posted by David Smith on 30 Sept 2001, 8:55 p.m., in response to message #1 by Brian I fixed one by cutting a rubber "O" ring and feeding it under the flex circuit. I first removed the remains of the old rubber strip with a small dowel rod. The thing has been running for around 5 years since I made the repair. I don't know what material the "O" ring was made of. It came out of a junk pile. It was the right thickness and was around 6 inches in diameter.

Re: HP-41C flex circuit problems Message #3 Posted by Brian on 30 Sept 2001, 9:20 p.m., in response to message #2 by David Smith Thanks David. My initial repair is already showing signs of trouble. My CX doesn't like anything plugged into port 4. Time to visit Pep Boys Automotive and get a few o-rings.

Re: HP-41C flex circuit problems Message #4 Posted by Vieira, Luiz C. (Brazil) on 1 Oct 2001, 4:05 a.m., in response to message #1 by Brian Hello. I saw a post at Classified Ads where one was selling a sort of 41`s Battery/IO mount (20, if I am not wrong). If I am in USA and I am lucky enough, they are already with me, but I'm in Brazil. I also have a Bat/IO mount with part of the flex already destroyed by corrosion and I thought about how to rebuild it, since I have no chance to repair the flex itself. I will try a slice of PCB with the copper trails in the same alignment (easy, cause they are standard size). As only two of them are devoted to the batteries, one side will be fully soldered to the remaining flex, and the other will have just to soldering points to the battery contacts. In fact, I think that rebuilding the batteries contacts and wiring them to the PCB slice will be better. As soon as I have something, I'm sending some material (even photos). All of this to tell I didn't get success repairing the Bat/IO mount... Is there any lab in USA that would produce just that flex for selling? I think a lot of people would buy it.

Re: HP-41C flex circuit problems Message #5 Posted by David Smith on 1 Oct 2001, 5:22 p.m., in response to message #4 by Vieira, Luiz C. (Brazil) Just about every hobby shop and hardware store in the US has a display of small brass strips, rods, tubes, angles, and channels made by K&S Engineering. You can find a brass channel (I don't remember the size) strip that fits over the battery contacts perfectly. Since the strips are 12 inches long, you can cut a bunch of battery contacts out of one strip. Just cut off a piece a little shorter than the HP41 battery contact and solder the ends to the remains of the corroded contact. I usually glue it down first. In extreme cases of corrosion you have to cut off the remains of the old contact, solder a thin wire to the new brass strip, glue down the new contact, and route the wire to one of the port connector power connections. If you are careful you can solder the wire to the very inside of the port connector and not interfere with modules on the port. Either run the wire around the edge of the battery contact assembly or drill a hole through it near the base. You do not want to run the wire under the contact assembly.

Re: HP-41C flex circuit problems Message #6 Posted by Pavel Korensky on 1 Oct 2001, 5:32 p.m., in response to message #4 by Vieira, Luiz C. (Brazil) There is a company called GOODFELLOW (www.goodfellow.com) which is selling the base material for flex circuits (Kapton foil laminated with copper). It is possible to spray this material with photoresistive paint which is available from average hobby electronic store and you can make flex circuits at home, similar way like traditional PCBs. The only problem is, that the base material is not cheap.

Re: HP-41C flex circuit problems Message #7 Posted by Vieira, Luiz C. (Brazil) on 1 Oct 2001, 8:49 p.m., in response to message #6 by Pavel Korensky Thank you for the precious information. Outside here, information do not come so easy...

Re: HP-41C flex circuit problems Message #8 Posted by Iqbal on 1 Oct 2001, 8:58 p.m., in response to message #7 by Vieira, Luiz C. (Brazil) Hey Luiz, if you ever finish that subdivision program for me, i'll send two of those flex assemblies your way. oh don't forget they're 'brand new in hp bag' and all.

Re: HP-41C flex circuit problems Message #9 Posted by Vieira, Luiz C. (Brazil) on 2 Oct 2001, 9:22 a.m., in response to message #8 by Iqbal Sorry, falks... this is just about a previous translation. What to say? I´ve been working this very weekend, and I have found a better approach to the calculus, using normal input as you want, with as many sides. I´m sending you an e-mail tomorrow... Thanks and forgive my silence. I did not forget.

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