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Needing more advice with my HP-48S - Printable Version

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Needing more advice with my HP-48S - Palmer O. Hanson, Jr. - 09-18-2011

On 14 May I reported:

I left the cells in my 48S longer than I should have. One of the cells leaked. The leakage got into the foam that provides the spring for the cell contacts. The leakage dissolved (if that is the correct word) the adhesive that attached the cell contacts to the foam. I have cleaned the compartment and have demonstrated that the calculator still works by simply holding the contact against the foam while inserting the cells.

I think that some of the leakage is still in the foam. How can I remove the leakage safely? What adhesive should I use to attach the contact to the foam? If I replace the foam where do I find foam that does not deteriorate in a few years?

I now find that I have a new problem with my HP48S. If I press either the 2 or the 3 key the number 23 appears in the screen. Similar effects occur with the 5 and 6 keys, the 8 and 9 keys, and the . and SPC keys. Similar effects also occur with pairs of keys which are not part of the numeric keyboard. For example, if I enter 9 at level 2 and 2 at level 1 and press y^x I would expect to see 81, Instead I see 22.36159094 which indicates that the calculator took the square root of two and then raised 9 to the square root of two power. Similar effects appear with other adjacent pairs of keys such as EEX and DEL, etc.

If I place the calculator under a reading lamp for a couple of hours it will operate properly for a few minutes and then will return to the operation described above. I think this means that some of the cell leakage may have gone into the electronics compartment, perhaps under the keyboard. This is certainly possible since the cell compartment is not a bathtub as was the case with the HP-35, HP-45 and HP-80. So, my questions are:

How do I open the the device to inspect for cell leakage and to clean if necessary?

Or, am I better off simply keeping the calculator warm?

Re: Needing more advice with my HP-48S - aj04062 - 09-18-2011

You can search the internet for methods to open this or the 48G series. I have found good luck using the method

However, fixing corrosion in the keyboard is a whole other thing. It requires a lot of work to take the keyboard assy apart.

Edited: 18 Sept 2011, 11:03 p.m.

Re: Needing more advice with my HP-48S - Martin Pinckney - 09-18-2011

How do I open the the device to inspect for cell leakage and to clean if necessary?

Palmer, here is some information I downloaded a couple of years ago. But be advised I have not tried it myself, so you are better off listening to someone who has!

Re: Needing more advice with my HP-48S - Bart (UK) - 09-19-2011

Hi Palmer,

I recently opened a 48SX to the point of taking the two halves apart. That is do-able, although I still have to take the faceplate off to re-sit the big heat stakes.

However, I have noted that the keyboard is put in place with a metal backing plate that is held in with dozens of small short heat stakes, and I think it almost impossible to put back together if taken apart (about 1/3 of them are visible in TOPWORK.JPG from Martin Pinckney's reference). I don't know if maybe the keyboard can be cleaned in-situ (once the electronics is removed) as per Geoff Quickfall's Voyager method (as described in this thread, Geoff's message on 10 Dec 2010, 9:31 p.m).