Another One Bites the Dust



#25

Doesn't sound like this guy read the manual.

Auction


#26

Could you enlighten those who also don't have/read the manual to what exactly is wrong? Is there something in the manual that says how to prevent the batteries from leaking? Is there something you know that is happening to the calculator that the seller and potential buyers don't know? Thanks!


#27

Never connect the charger unless you are sure the battery package is in good shape! Otherwise chances are high you blow the ACT chip which is not reparable.


#28

Exactly, I think this seller thinks the battery is to blame for the unit's strange behavior. I think it is fried and that is the reason. I think he even described it's demise.

#29

Poor little baby...

If this guy insists on doing so, we'll soon be told about an 'HP25C's barbecue'...

Too bad.


#30

I do blame HP's design team a little for making the electrical system the way they did. Is it hard to anticipate dufuses that will barbeque the HP-25 the way some do?

Namir


#31

Quote:
I do blame HP's design team a little...

A little??? That's pretty tolerant of the most incompetent, almost criminal example of poor engineering in all the history of calculator manufacturing by any outfit. This was at the peak of HP's ill-deserved reputation for special quality...and while wonderous St. Hewlett was still at the helm. It was all marketer's mythology sold to credulous believers.

If a company makes devices (expensive ones at that) that will be destroyed by a customer's single simple natural error, or by conditions that will always develope as the battery ages, then that company deserves nothing but contempt.


#32

Quote:
most incompetent... example of poor engineering...

Not their best engineering work, I guess. Having owned a 67 for 5-6 years, I was dismayed - no, angry - when I learned by bitter experience that my expensive, powerful new 41CV was housed in a type of plastic (polystyrene?) that was nearly as shatter-prone as my old TI slide rule calc. that cost hundreds less.

#33

Definitely the design is a problem. Mistakes happen.

I remember a laserjet that actually ran the front panel off the computer's parallel port when the printer was turned off but connected. That was bad. Also bad is that some parallel ports on some systems did not have current limiting resistors on the signal lines. Combine the two and computer motherboards were fried, both desktops and laptops. That was worse. The laserjet side was definitely a mistake. The computer side seems like an intentional manufacturing cost reduction (save board space and the cost of 17 resistors) but might have been a mistake.

Is there a simple mod for the HP25 that will protect it from a charger 'accident' while not losing any functionality? (In other words, a mod to correct the design?)


#34

Yes ... use the HP-25 emulators for the iPad. You can operate these babies without worrying about batteries, chargers, or current.


#35

Quote:
Yes ... use the HP-25 emulators for the iPad. You can operate these babies without worrying about batteries, chargers, or current.

Except that you would need a charger practically every day, and that when the battery dies you can't replace it. Oh, and if you liked the good HP keys, forget about them - forget about keys *at all* for that matter! :)


Couldn't a current limiter (or a voltage limiter, kind of like the 7805) be used in series with the charger to avoid problems?


Edited: 24 June 2012, 11:40 p.m.


#36

I had a 25 on my desk for many years. I had modified it with capacitors, a resistor and a zener diode so I could run it without the powersupply.
I suppose if you don't need it to run when the battery gets disconnected or dies, just Zener diode accross the battery terminals would do.

My 25 died after about 5 years of running (I never turned it off). I am pretty sure it wasn't related to my modification, but haven't found a reson for its demise. Maybe it just couldn't handle the continous operation.


#37

Seems five years are a good minimum lifetime for a 25C. Bought mine (a repaired unit) in the seventies and sold it after five years of heavy on- and off-line usage to a fellow student - replaced it by an 11C then.

BTW, I didn't know about the battery charger design flaw at that time and therefore didn't take care of it at all - but maybe the repair person took care of that already (will never know). IIRC this person was a guy who learned that job at HP - at that time there was a technical HP affiliate in Germany, too.

Edited: 25 June 2012, 4:44 a.m.


#38

Mine wasn't a 25C, just a normal 25.
My very nice 25C wouldn't end up on the desk for daily use. Got the WP34S for that :)
And if I don't use that, I prefer the 15C for daily use, or the 42S if I do complex calculations. Or a 25 (I replaced the broken one), the woodstocks just have a very nice feel to them.


#39

Please remember there wasn't any 15C, 42S, or 34S at that time ;-)


#40

Quote:
Please remember there wasn't any 15C, 42S, or 34S at that time ;-)

I know, but given todays alternatives, I would rather keep the 25C in good condition :)


#41

Agree on that for sure :-) Woodstocks had the best packaging ever IMHO.

#42

Look for old posts written by Norm, a.k.a. "Captain Zener"; IIRC he explained a simple modification by addition of a particular type of zener diode which protects the HP 25 and similar units without causing any trouble.

Safest option: NEVER use the charger again, charge your batteries in an external charger (this is also better for NiMH batteries, instead of NiCd).


#43

Quote:
Safest option: NEVER use the charger again, charge your batteries in an external charger (this is also better for NiMH batteries, instead of NiCd).

I think it is ok to use the charger, if you switch the calculator OFF before you connect it, and remove the charger before switching on again.

#44

Quote:
I think it is ok to use the charger, if you switch the calculator OFF before you connect it, and remove the charger before switching on again.

Only valid for non-continuous memory models. All Woodstock C variants will still suffer damage.

#45

In all continuous memory models, RAM chips are permanently connected to batteries, to receive the standby current (or voltage, if you prefer) needed to keep their contents; so the power switch in OFF position is not enough to prevent excessive voltage to reach these ICs if the batteries fail to act as a regulating device.

Again, please play it safe and recharge outside the calculator.
And, when using current (pun intended) NiMH batteries, which have a larger capacity compared to the original NiCd cells, a modern, external charger will be more convenient than the slow and non-smart charging circuit on the calculator.

#46

Quote:
Look for old posts written by Norm, a.k.a. "Captain Zener"; IIRC he explained a simple modification by addition of a particular type of zener diode which protects the HP 25 and similar units without causing any trouble.

Don't waste your time, it did not work. The zener leakage current was too high, draining batteries for no good reason and the diode would fail due to its low power rating if it ever saw the full voltage from the charger.

In short, there is no simple change to prevent damage. Charging batteries externally is the only good solution.


#47

Randy,
Thank you for clarifying this issue.
Best regards

#48

Quote:
Don't waste your time, it did not work. The zener leakage current was too high, draining batteries for no good reason and the diode would fail due to its low power rating if it ever saw the full voltage from the charger.

In short, there is no simple change to prevent damage. Charging batteries externally is the only good solution.


Darn. Guess then it would have to be a crowbar with a power FET and a suitable fuse in line. Definitely not simple.

Oh well. I'll keep charging my 25 batts 'standalone.'

thanks!


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