The Museum of HP Calculators

HP Forum Archive 14

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Message #1 Posted by Paul Marin on 4 Oct 2004, 8:29 p.m.

I was about to sell my 48G to a guy in the USA, until I took it out of storage and powered it up with some new batteries. On start up, I get slow keystroke response, the right shift appearing all the time and it won't go off. The calculator takes too long to any calculations and they take longer to appear on screen. I've ried everything, including shorting the terminals with batteries out (advice from HP head office here in Australia) I'm at the point where I want to break it open, just to see if the right shift key may be stuck. I've done all the self help available in the manuals but nothing worked. I don't care if I break it because I have other units that I use. Can anyone advise a solution otherwise I'm going to take a hammer to it. I dont want to because it was a nice unit when I first got it. But I put it away for future use, just in case, but bought a 33S instead

Thanking in advance

Paul Marin

Re: HP48G
Message #2 Posted by Randy Sloyer on 4 Oct 2004, 9:49 p.m.,
in response to message #1 by Paul Marin

Don't take a hammer to it, it's pointless. Opening the unit will bring you no closer to a solution, only closer to a pile of useless electronic bits.

Yes, it is a shorted key. A closed key is somewhere around 10k ohms. Anything from 10k up to several meg ohms will result in the behavior you are seeing. The offending key will usually be displayed with very slow response.

Try a few drops of isopropyl alcohol around the key, allow to penetrate for a second turn on it's side and press a few times. Repeat once or twice and allow to dry. An ultrasonic cleaner works well for these problems if the simple flush doesn't work.

You'll find problems of this type fall into one of two possibilities. One, it was just some crud that worked it's way into the key and it will be good as new with cleaning. Two, it will work for a while but then the problem comes back. Those you'll find to be migration of the conductive material from the top half of the switch embedding itself in the bottom cross point with each key press. Those are destined for the rubbish bin.

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