Erratic display after 25 years

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Erratic display after 25 years

Postby cottagefarmer » Thu Jan 14, 2016 10:53 pm

Hello, like I'm sure many have come on here to say, I tried to resurrect my old 41CV and having an issue.

The display almost looks like there's a short on one or more buttons. After reset It will say "LN" first, then "Null", then "Tan" then "Null", then "Data Error", etc. Then as I type other buttons weird results. It also wants to go into PRGM mode a lot - and stops on a numbered instruction (like 02 LBL 01) - this happens a lot. And since it stops there it leads me to believe it's not a stuck key.

I saw some instructions on cleaning the keyboard, but before I do this does that sound like the problem to you all? Or does this sound familiar in some other way?

Thank you in advance,
Patrick (Dallas)
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Joined: Thu Jan 14, 2016 10:46 pm

Re: Erratic display after 25 years

Postby lunasix » Thu Mar 17, 2016 4:33 pm

Hi Patrick,

maybe your 41CV suffers from short circuit(s) among the bare wires between the keyboard and the display board. Review my contributions of Apr 26, 2009, May 10, 2009, and Apr 20, 2011. The LN, TAN, and SST keys lie in a column (rightmost on the keyboard) which makes me think of something going wrong with the corresponting column scan wire. Also the R/S key down there in the same column is a powerful candidate to make things go runaway in an unwanted manner. Stuck or bridged keys are less probable also to my opinion, at least as long as the unit has not been challenged by too messy an environment; though, In one of my units I really had to dismantle and clean the entire keyboard, and I reassembled it with strips of kapton tape in place of the original cover foil, but from that time on, it runs like new (nearly 7 years now).

good luck

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Joined: Sun Apr 26, 2009 11:58 am

Re: Erratic display after 25 years

Postby Garth » Thu Mar 17, 2016 8:22 pm

lunasix wrote:Review my contributions of Apr 26, 2009,

at viewtopic.php?f=2&t=62&p=169#p169

May 10, 2009,

at viewtopic.php?f=2&t=64&p=176#p176

and Apr 20, 2011

at viewtopic.php?f=2&t=62&p=417#p417 (60 HP-41 links on the links page)
Posts: 156
Joined: Tue Jan 20, 2009 1:31 am

Re: Erratic display after 25 years

Postby longkeeler » Sat Apr 02, 2016 6:40 pm

After about 30 years of reliable service, my HP 41CX all of a sudden and out of the blue also developed symptoms that resemble the ones described here. First, no reaction to the ON button at all, just ten minutes after I had used it totally normally before; then, first, I thought the batteries were gone, though replacing them didn't bring any avail. Pressing the PRGM, <- and R/S switch at the same time led to 'clx' in the display, followed by a '0, 00'. Batteries out and in again led to variations of this behaviour,some times I could enter a single digit, mostly not, but did not lead further. One of the battery springs (the one of the inner pair where the plus pole of the cell sits) showed a small patch of oxidation which could be wiped away with a glass brush. No help though.

My HP41CX has always lived on my desk, no harsh environment, no pushes, no droppings. After reading the descriptions here, I reckon it as pretty probable that it needs the described contact care procedure. Are there any tutorials or descriptions on YouTube or somewhere helse that make things even easier than described here? Expecially the opening of the housing and the proper disassembly would be interesting.

And what do you folks recommend as a cleaning medium? Water? Iso-propanolol? Or?

Thanks a lot in advance, also for keeping and taking care of this website. I still remember the time that HP sent me a quarterly user magazine after I head purchased my first HP 65 (after the HP55, which was my first, then followed by an HP67). The HP41 CX is still unbeatable (except for comatic phases like now).


Ulli aka longkeeler.
Don't try to fix it if it is not broken. And IF it is broken, please keep your fingers away!
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Joined: Sat Apr 02, 2016 5:05 pm

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