proximal display clamp syndrome

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proximal display clamp syndrome

Postby lunasix » Sun Apr 26, 2009 1:44 pm

Reports about HP-41s ceasing operation or displaying strange characters for dropping, or no apparent reason at all, or recurrent MEMORY LOST episodes, start sounding familiar to me. A possible cause for this disorder is the lower (or proximal) of the steel spring rails (clamps) holding the display assembly, which shorts out several of the conductor traces on the top edge of the keyboard P.C. Such a short totally messes up the communication with the display controller and makes the HP-41 going crazy.

This was the case with my seemingly dead HP-41CV (SN 2117S11461). A piece of insulating tape applied to the lower display clamp rail perfectly cured the unit, which is now back in charge on my engineering desk.

For doing this repair, some minor surgery is inevitable however. The keyboard P.C. needs to be removed, or the display desoldered. I prefer removing the keyboard P.C. for this allows thorough cleaning of the keyboard and of the display at the same time. For dismantling and cleaning the keyboard (it is easier than it sounds), I will post detailed instruction if there is interest.

Luc
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Re: proximal display clamp syndrome

Postby aurelio » Sun Dec 12, 2010 1:36 pm

I have a problem with my HP 41c (see please may post) and I should appreciate if you could give me more information: how can I remove the PC without to brake anything, thank-you very much
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Re: proximal display clamp syndrome

Postby lunasix » Wed Apr 20, 2011 8:27 pm

Sorry to be back only this late. Well it takes something like a front-cutting forceps to cleanly clip off all of those numerous plastic rivets. Electronics enthusiasts use such things for stuffing P.C. boards. I use an EREM 582 E cutter which ist best suited to my opinion. Not exactly cheap but will do the job (and many more), and the HP41 isn't either. When all rivets are gone, the keyboard P.C. board can be gently removed by grabbing it by the edges with a small screw driver. Usually this is the moment when the keys jump or fall out onto the desk into a big mess - no problem, the yellow pictogram on the rear of the calculator will help realigning them later. After cleaning the keys and the frame (in a ultrasonic bath e.g.) reinsert the keys and the (also cleaned and inspected) keyboard P.C. board. The now missing rivets are substituted by applying small dabs of solvent based contact glue (NO acrylate superglue PLEASE as this is smelly messy stuff and will impair electrical contact surfaces overall, and discolorate its surroundings over time!) on all rivet positions, making sure no glue contaminates the zebra strip connector areas. If it does by accident, some acetone on a tissue will remove it. Carefully lay the assembly facing bottom on the desk, distribute some small objects like screw nuts (all the same size) as spacers between the glue dabs, then a heavy book or the like on top to press down the P.C. into the frame, and let dry overnight (or, still better, two days). This procedure can be repeated if unsatisfactory, as the glue isn't that hard to remove again. ONCE AGAIN - NO acrylate superglue! This is disastrous & strictly forbidden inside delicate electronic equipment. The keyboard is now operative again but should not be used prior to final assembly of the calculator because it needs mechanical support from the zebra connectors to withstand the pressure from the keys. My calculators are runnung both fine for several years since this procedure.

Luc
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