HP Forum Archive 21

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Another One Bites the Dust Message #1 Posted by aj04062 on 23 June 2012, 10:37 p.m. Doesn't sound like this guy read the manual. Auction

Re: Another One Bites the Dust Message #2 Posted by Lode on 24 June 2012, 4:56 a.m., in response to message #1 by aj04062 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!

Re: Another One Bites the Dust Message #3 Posted by Marcus von Cube, Germany on 24 June 2012, 5:25 a.m., in response to message #2 by Lode 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.

Re: Another One Bites the Dust Message #4 Posted by aj04062 on 24 June 2012, 9:19 a.m., in response to message #3 by Marcus von Cube, Germany 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.

Re: Another One Bites the Dust Message #5 Posted by Luiz C. Vieira (Brazil) on 24 June 2012, 9:28 a.m., in response to message #1 by aj04062 Poor little baby... If this guy insists on doing so, we'll soon be told about an 'HP25C's barbecue'... Too bad.

Re: Another One Bites the Dust Message #6 Posted by Namir on 24 June 2012, 12:48 p.m., in response to message #5 by Luiz C. Vieira (Brazil) 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

Re: Another One Bites the Dust Message #7 Posted by Mike Morrow on 24 June 2012, 1:29 p.m., in response to message #6 by Namir 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.

Re: Another One Bites the Dust Message #8 Posted by Michael Craig on 24 June 2012, 2:07 p.m., in response to message #7 by Mike Morrow 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.

Re: Another One Bites the Dust Message #9 Posted by sylvandb on 24 June 2012, 5:44 p.m., in response to message #6 by Namir 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?)

Re: Another One Bites the Dust Message #10 Posted by Namir on 24 June 2012, 6:58 p.m., in response to message #9 by sylvandb Yes ... use the HP-25 emulators for the iPad. You can operate these babies without worrying about batteries, chargers, or current.

Re: Another One Bites the Dust Message #11 Posted by Cristian Arezzini on 24 June 2012, 11:38 p.m., in response to message #10 by Namir 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.

Re: Another One Bites the Dust Message #12 Posted by Harald on 25 June 2012, 4:29 a.m., in response to message #11 by Cristian Arezzini 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.

Re: Another One Bites the Dust Message #13 Posted by Walter B on 25 June 2012, 4:38 a.m., in response to message #12 by Harald 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.

Re: Another One Bites the Dust Message #14 Posted by Harald on 25 June 2012, 5:31 p.m., in response to message #13 by Walter B 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.

Re: Another One Bites the Dust Message #15 Posted by Walter B on 25 June 2012, 5:38 p.m., in response to message #14 by Harald Please remember there wasn't any 15C, 42S, or 34S at that time ;-)

Re: Another One Bites the Dust Message #16 Posted by Harald on 26 June 2012, 5:45 a.m., in response to message #15 by Walter B 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 :)

Re: Another One Bites the Dust Message #17 Posted by Walter B on 26 June 2012, 8:26 a.m., in response to message #16 by Harald Agree on that for sure :-) Woodstocks had the best packaging ever IMHO.

Re: Another One Bites the Dust Message #18 Posted by Andrés C. Rodríguez (Argentina) on 25 June 2012, 1:16 p.m., in response to message #9 by sylvandb 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).

Re: Another One Bites the Dust Message #19 Posted by Kees Bouw on 25 June 2012, 2:07 p.m., in response to message #18 by Andrés C. Rodríguez (Argentina) 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.

Re: Another One Bites the Dust Message #20 Posted by Randy on 25 June 2012, 3:13 p.m., in response to message #19 by Kees Bouw 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.

Re: Another One Bites the Dust Message #21 Posted by Andrés C. Rodríguez (Argentina) on 25 June 2012, 3:20 p.m., in response to message #19 by Kees Bouw 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.

Re: Another One Bites the Dust Message #22 Posted by Randy on 25 June 2012, 3:08 p.m., in response to message #18 by Andrés C. Rodríguez (Argentina) 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.

Re: Another One Bites the Dust Message #23 Posted by Andrés C. Rodríguez (Argentina) on 25 June 2012, 3:13 p.m., in response to message #22 by Randy Randy, Thank you for clarifying this issue. Best regards

Re: Another One Bites the Dust Message #24 Posted by sylvandb on 26 June 2012, 11:16 p.m., in response to message #22 by Randy 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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