Reading this makes me weep.



#34

I read this TAS listing and it saddens me greatly that this sort of buffoonery happens so often with ignorant sellers.

TAS listing

Read the Q&A at the end.


Edited: 8 Feb 2011, 8:17 p.m.


#35

As dumb as these people are, HP was "dumb" to design a piece of equipment this way.

#36

Well, the "buffoonery" it's really HP's fault for doing such a shoddy power supply design. It would have only taken two additional components (under $0.15 cost in volume production) to have a better power supply that wouldn't fry the electronics if the battery was dead or missing.

Fortunately HP didn't design any more calculators or accessories with that kind of power supply after 1979, but it definitely is sad that probably a lot of the old ones get destroyed by people who are unaware of the problem.


#37

Eric, I agree the design is poor at best. But, given the constraint of keeping electronics out of the wall wort, what are the two fifteen cent parts that would protect the calculator from over-voltage?

I'm asking because even if it costs several dollars at today's prices, I'd install them in all my Woodstocks and any that I repaired.


#38

A zener diode and a series resistor. The only trick is getting the right zener voltage such that it protects the circuitry while not interfering with charging. The required zener voltage is not a common one; the minimum order quantity to get it is more than 5000 pieces. This would have been no problem for HP, but makes it less likely for us to install it ourselves.

Without using the uncommon-valued zener, it can be done with more circuitry using commonly available components. Then it becomes more difficult to pack the added circuitry into the calculator.


#39

given (i assume) the calculator runs on a pair of AA ni-cads assembled into a battery pack, the solution is a chunky 3.3 volt zener diode connected directly across the battery contacts. a 1 watt suitable component is the 1N4728A, listed from farnell (their p/n 1467572) for the princely sum of 20.4 cents(nz) each in quantities of 1. no additional series resistor is needed - see below.

now, the ni-cad cells would have had a capacity of perhaps 700mA/h back then, and the charging technology of the day would dictate a maximum safe charging current of 1/10th of that for a 10 hour rate, or 70mA. 70mA x 3.3 volts = 0.23 watts dissipation by the zener (worst case), well within the power rating. even charging at a 3 hour rate, it is still only 230mA x 3.3 volts = 0.76 watts.

note that the zener would ONLY have any effect if the batteries were NOT plugged in. with a battery pack present it would dissipate nothing, with the maximum voltage across a pair of fully charged ni-cads falling well below the 3.3 volt clipping voltage (ni-cads top out at about 1.5 volts at the peak of their charge cycle).

cheers,
rob :-)

Edited: 9 Feb 2011, 8:07 a.m.


#40

Hi Rob, looks like a nice and cost-effective solution.

Quote:
now, the ni-cad cells would have had a capacity of perhaps 700mA/h back then,

For sake of not confusing our friends, such capacities are measured in mAh (or mA*h if you like).


#41

Quote:
...such capacities are measured in mAh (or mA*h if you like).

That depends on if one is talking about battery capacity (milliAmpere-hour) or nonsense capacity (milliAmp per hour). :-)


#42

Quote:
That depends on if one is talking about battery capacity (milliAmpere-hour) or nonsense capacity (milliAmp per hour). :-)

d:-D Oh yes! Please see
below ...
#43

Quote:
note that the zener would ONLY have any effect if the batteries were NOT plugged in. with a battery pack present it would dissipate nothing
That's the theory but it's not reality.

With a 3.3 volt part, you'll have at least 5 ma of leakage at 2.8 to 2.9 volts, the point at which the cells are at full charge. So, you end up with a fair amount of self-discharge making the scheme impracticable. Been there, tried that.


#44

and at 2.6 volts? this would be close enough to full charge as to not matter for the loss.

if leakage were a problem, there are two solutions that come to mind immediately:
1. place the zener the other side of the power switch, or,
2. put an NPN transistor in series with the zener (at the ground end), with the base tied (via a 10k resistor) to the calculator's Vcc line. the transistor could be quite small.

addendum - a quick check reveals: 3.3 volt zener (BZX79C3v3), two ni-mh batteries freshly charged giving 2.7 volts, produces a measured leakage current of 800uA. this would (assuming the voltage didn't drop) give a battery life of 36 days. i believe practice would be much better, well exceeding the self-discharge of 1970's technology ni-cads.

Edited: 9 Feb 2011, 10:28 a.m.

#45

AA-size NiCd cells had *at best* about 450 mA-hr capacity in the mid-1970s when the Woodstocks were in production.


#46

Mike,

Quote:
AA-size NiCd cells had *at best* about 450 mA-hr capacity ...

You can't subtract apples from pears, as people say here, so your "unit" doesn't work. Two, and counting d;-)

#47

I know. I once operated nuclear submarine batteries for a living.

The traditional term for battery capacity in many English texts has been "Ampere-hour" rather than the awkard scanning "Amperehour". The "-" is there as a delineation between the two words in the compound term, and not as a mathematical function. It causes no ambiguity in unit world because there are no additive or subtractive unit combinations that make sense.

But you are correct...the best unit would be "Ah". I should have used that. :-)

Edited: 9 Feb 2011, 11:17 a.m.


#48

Mike, I didn't complain about the Ampere-hours in the plain text of your posting above (we have them in one word here: Amperestunden). But as you've acknowledged, as soon as you abbreviate them, universal math rules apply. Science and engineering have some easy sides, too 8)


#49

Quote:
Mike, I didn't complain about the Ampere-hours in the plain text of your posting above...

Ah, (pun intended) but you could have: When written out, the first letter of the unit should not be capitalized, except for other reasons (e.g., beginning a sentence, or if in all caps). I was mildly chastised for such a mistake years ago.

I don't know if accepted practice differs around the world, but that's ours.

-- Karl

Edited: 9 Feb 2011, 11:51 p.m.


#50

SI rules says some units (derived from names) should be ALWAYS capitalized in short form, including Ampere and Kelvin. So, "Ah" is correct, while "ah" is not.

http://physics.nist.gov/cuu/Units/units.html

In countries using different standard and numerical systems there could be another rules :)


SI prefixes should be always properly used either in capitalized or string form.

There are some crazy units, like Siemens, which denoted resistance until WWII and conductivity after it. If you read some books from the first half of XX and see "Siemens", sometimes it is hard to understand either it is resistance or inverse.

http://en.wikipedia.org/wiki/Siemens_%28unit%29

#51

Is this HP-29C repairable?
I mean would it work with a good battery pack installed?

Or have the actions from the seller destroyed it beyond hope?


#52

Usually the famous ACT-Chip has been fried. It can only be repaired by finding another one in another 29C (maybe also 25C) - but you won't disassemble a (usually working) donor for repairing a nonworking patient, will you? BTW, this topic was covered in this forum extensively several times, so you'll certainly find more about it in the archives.

Edited: 9 Feb 2011, 10:38 a.m.

#53

Quote:
buffoonery happens so often with ignorant sellers.

I don't know who the seller is, but unless he frequents this forum, I don't think it is fair to call him "ignorant."

Most modern electronics with batteries operate just fine with a charger, with or without the batteries - my most recent knowledge concerns my digital cameras. If his knowledge base is similar, he was doing what he is used to doing.

I consider myself fairly intelligent, and if I didn't know anything about this particular series of calculators and the likely problems that result if the charger is plugged in without the batteries (making good contact; another point one may not be used to thinking about), I would happily plug it in.


#54

"ignorant" comes from Latin "ignorare" = "not (to) know". So an ignorant seller is a seller who doesn't know (here: the bad design of the charging circuit of HP's Woodstocks). Since I've fried a 25C the same way once, I'd call me ignorant as well until then. No problem with that word.


#55

I understand what you are saying. However, in the U.S. the usage of the word "ignorant" has an extremely negative connotation and is usually considered to be an insult. It means to have a lack of knowledge in general - being uneducated, unsophisticated, and/or foolish.

Better words to use might be uninformed or unaware.

Regards,

Mark

Edited: 9 Feb 2011, 12:55 p.m.


#56

Quote:
I understand what you are saying. However, in the U.S. the usage of the word "ignorant" has an extremely negative connotation and is usually considered to be an insult. It means to have a lack of knowledge in general - being uneducated, unsophisticated, and/or foolish.

Perhaps Walter was ignorant of this. {;-)

#57

OK, Martin, 1 for you :-)

BTW, the word has a very negative connotation in German as well, translating to "wilfully ignorant" in English. Writers with Roman language background, however, may think closer to the original meaning.


#58

Quote:
Writers with Roman language background, however, may think closer to the original meaning.

So stop stealing our words and give them a (somewhat) different meaning! :-)

Today "ignorante" has a pejorative acception here too, but the true meaning is the one Walter reported.

Greetings,
Maximus


#59

Quote:
Today "ignorante" has a pejorative acception here too, but the true meaning is the one Walter reported.

Agreed. In Portuguese the word has acquired a very negative connotation, indeed a very offensive word, despite the original milder meaning. I guess the same applies to Spanish as well.

Cheers,

Gerson.

#60

Excerpt from the original poster:

Quote:
...this sort of buffoonery happens so often with ignorant sellers

From Mark:

Quote:
Better words to use might be uninformed or unaware...

And (slightly corrected) from Thomas Okken:

Quote:
...what you really mean to convey is "unknowing"...

Y'all missed the ideal word in English:

"unwitting"

Even "oblivious" is a better choice.

-- Karl


Edited: 9 Feb 2011, 11:34 p.m.


#61

Quoting the musical My Fair Lady:

"Why can't the English, oh why can't the English learn to speak?!" d;-)

Edited: 10 Feb 2011, 1:56 a.m.

#62

Walter, thanks for clarifying my comment. I was not criticizing the seller for his unfortunate actions that were the result of his ignorance, but simply lamenting the sad fact that so many Woodstocks are being destroyed this way. I too am guilty of ignorant acts, although fortunately none have not resulted in the destruction of a vintage calculator. When I acquired my first HP 65 it did not have a battery or Owner's Handbook, and I was unaware of the unique circuitry in this Classic model, which requires the presence of a battery to prevent damage to the card reader components. In fact, at the bottom of page 87 of the HP 65 Owner's Handbook there is a cautionary note that damage may occur if the calculator is operated from the AC adapter without the presence of a battery pack. I briefly operated the calc from the AC line before obtaining a battery, and fortunately no damage was done. As to my collection of Woodstocks, I now charge all the NiCad battery packs externally, and never connect the AC adapter to any of them.

#63

I believe "ignorare" means "to ignore". "Not to know" would be "nescire". Looked at it that way, the original meaning of "ignorant" translates to something more like "wilfully ingorant" in modern usage, and that is just a euphemism for "dumb", which is pejorative. In other words, never a good choice of words if what you really mean to convey is "unknowning". :-)


#64

etymology 1
etymology 2

Greetings,
Massimo


#65

Thanks for setting me straight! I was unaware that "ignorare" had multiple meanings even before the word was absorbed into English.

#66

Please see e.g. here. "To ignore" is "neglegere" in Latin -C[:-)

To bring it back on topic: CETERVM CENSEO: HP, COMPARA VNVM XLIII :-)

Edited: 9 Feb 2011, 5:29 p.m.


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