Help me alert regular users to dangers to their calcs



#14

I need suggestions where I might post info about how to avoid damaging vintage HP calculators.

I am going to create a page on my website with information for users of vintage HP calculators on how to avoid damaging them.

In particular I am concerned about those models that should not be run from the wall power supplies without a KNOWN GOOD Ni-cad battery pack installed in the calculator. In my calculator repair business I am seeing a lot of users that are unaware of this
situation. I can create a page on my site explaining this but what good will it do? None of the users that need to see this info are
likely to see it there in a timely manor. In spite of that I am going to create such a page of course.

What I need are suggestions from you folks. Do any of you have any ideas where users (as opposed to say collectors) might be alerted to this issue? About half of my customers are users, engineers (transportation, hydraulics, etc) , physicists (Fermi and Cern!),
mathematicians, surveyors, professors, design and such... Even medical doctors!


#15

Good morning!

Quote:
What I need are suggestions from you folks. Do any of you have any ideas where users (as opposed to say collectors) might be alerted to this issue? About half of my customers are users, engineers (transportation, hydraulics, etc) , physicists (Fermi and Cern!),
mathematicians, surveyors, professors, design and such... Even medical doctors!

Just out of curiosity: Are the persons on your list really _users_ of vintage LED calculators? Regular, day-to-day users of Hp-19, 21, 25, 27 or 29 (the only calculators that really badly suffer from charger overvoltage)? I find that hard to believe. My dad used to work as a physicist in a research facility and when he retired more than 15 years ago, he was the only one in his group who still used his Hp67.

Regards
Max

#16

It would be useful to point to some simple device which can confirm that the battery pack is still within specification. Otherwise, how is a non-engineer to verify that they have a "KNOWN GOOD" battery pack?

Nick


#17

First to the question regarding are these actual users of said calculators. Yes they are, and I'll be the first to admit that I was just as surprised by how many of them there are as you are skeptical about their numbers. I totally understand your skepticism. I can only add, I have documentation if you'd like to see it?

As to the second question. How is a regular user supposed to verify that they have a "KNOWN GOOD" battery pack? An astute question
and one which was in the back of my mind when I composed the original post... You are right I shouldn't have left that info out. If there is a battery pack in the calculator and one wishes to verify that it is 'KNOWN GOOD", unplug the wall charger from the calculator and turn the calculator on and check to see if the battery pack provides a constant supply of power for a reasonable time period. If not is fails the test.


#18

Hello!

Quote:
I can only add, I have documentation if you'd like to see it?

No no, I believe you :-) Was just wondering. Myself, I have worked in engineering, research and IT since finishing university in 1986 (but changed profession a few year ago) and apart from myself have never seen anyone using a vintage LED calculator. Not one in all those years!

And regarding my own vintage HPs: I replace the original 500mAh NiCd batteries with 2000-2500mAh NimH cells. They cost next to nothing and last four to five times as long as the original ones. I only need to recharge them rarely (don't really have anything to calculate anyway outside MS Excel) so putting them into an external charger for this is no big hassle.

Regards
max


#19

Well as I said above I am encountering more issues with this than I'd like to see and I know there are some VERY well informed folks here so thought I should ask. If we can locate some promising places online to post this information I will do so and maybe we can keep more of these great devices in operational condition.

I have been told be several customers that they intend to pass their vintage HP calculators on to the children and grandchildren (usually when they enter college or university).

#20

There's no such thing as a "known-good" NiCd pack for the calculators in question. The reason is because even a good pack can go bad while the calculator is plugged in and then the calculator's guts fry as the calculator screams its death knell. This is a severe and unfortunate design defect of these machines. Using a component like a battery pack as a voltage regulator was not a good idea.

Those in the know (I'm not one of them) never connect a charger to these calculators. They charge the pack externally in an external HP charger module or they convert the calculator's battery pack so that it uses rechargeable AA batteries and they recharge the AA batteries externally.


#21

Steve - I agree with everything you say. (Well I mean how could one not?) Personally I believe that removing the battery pack on a regular (and tight) schedule and testing it's condition will work, but I agree that your approach removes the risk. I will consider adding what you suggest to anything I publish. As for this being a design flaw, well it surely seems like a major one. In defense of my friends that helped create these designs I would point out that (for example) some HP equipment from the same period used lead acid batteries. Yes this is a
metaphoric attempt to say that batteries were all to similar to stone knives at the time. If I remember correctly, cheap stable solid state regulars were still a couple years off. Last year I spent some time working on a HP9100B (circa. 1971) First it's design was way outside my area of technical experience. But I could write a thesis about what the design of that calculator reveals about how much we DIDN'T know yet. But I digress.


#22

Quote:
Personally I believe that removing the battery pack on a regular (and tight) schedule and testing it's condition will work, but I agree that your approach removes the risk.

I was thinking of something along these lines. Perhaps you can recommend a battery tester that has the required specifications.

Nick

#23

Bruce,

I worked for HP during this period though in Loveland, not Corvallis. Significantly, the HP 35 and its brothers did not have this problem and could work with no battery pack at all. The second generation was a cost-down series and protection from self-destruction by the charger didn't make the cut. Batteries are troublesome, no matter what. That's for sure.


#24

Is there a chance to use a regulated power supply instead? It should do double duty (charging and powering the calculator) if at all possible.

#25

Bruce, have you considered social networks (Facebook, Google+, LinkedIn and others)? And this place (the Museum, not the forum) of course!


#26

I suppose Linkedin might be a possibility but I haven't used it much but if I can I will check it out - thanks.


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