fix an HP 41C tall key - fullnut



i have a cosmetically perfect HP 41C tall key - fullnut from the early '80 or late '70 (not in mind the SN today),
but it is very hard to power on it, it use to works sometimes after inserting betteries, when working all functions are correct thus the card reader does not seems to be recognized (as far as i remember can't see it in cat 1,2,3), but when i power off it is very hard to power on again unless i wait a long time (hours,days... since i did not use it often)
(not a battery problem or card reader conflict,tested with and without on others HP41C/CX)
HP41C tall key does not work better without card reader,
as it is in perfect condition with no corrosion inside or any crack there should be a solution,
does any one know what components must be replaced or the reason of the problem?
note: when opened all contacts are perfect plastic not broken not a simple connection problem,condensators seems okay but not tested...




I'd suggest They did a great job on my Blanknut...


Hey, Dave!

Missed you this year at HHC2008!




Hello Damien,

If you can get ahold of a barcode scanner wand for your 41, plug it in and press the button (on the wand), and that should power up the calculator. If your machine will power up this way, it could indicate a bad keyboard contact under the ON/OFF rocker switch.

Best Regards, Hal


i find a way to power on,
1-remove the battery for a long time or invert (yes) the battery for one or two minutes (no risk as diodes protect the calculator)
2-calculator show 'memory lost' or pressing power on and it will show 'memory lost'
3-execute 'ON' command as when power off it will not start again having done all the steps, so the calculator will not power off automatically for saving batteries.


If everything looks good mechanically, it is most likely a rom or d/s failure. The only way to test is with an HP service module.


evrything looks ok,all screw are tighten correctly,opening it and disassembling show no damage, the 4th port sometimes seems dead but with some flex on case works again,the calculator power on only if i remove the batteries for hours or invert the batteries for 1-2 minutes, so i leave only 2 batteries inside and 2 other stay in case,when i use it i put in place all the batteries, power on it , execute 'on' command to keep it running for hours ,after i stop it with power off button (or 'off' :-) ) and store it removing 2 or all the batteries (i remove only two because i can place only two batteries in case as i have a card reader ,the two unused batteries take place in the hole on the card reader where HP il module can pass by ,in paper too to not scratch anything), that's all...


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