HP Forum Archive 14

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*Unused* HP-21 apparently dead - Please help! Message #1 Posted by Jorge on 3 Mar 2004, 12:02 p.m. Hi & greetings from NW Spain! I have an HP-21 calculator in *unused* mint condition. It worked fine the first day I received it but not so the second... I tried to switch it ON but did not work anymore (why, if I did not anything??). The display does not produce any sign of activity. I've checked the battery pack with an electronic tester and it provides good charge level. Also, there's no sign of corrosion by acids on the battery-compartment contacts or in the battery itself. What could be happened here? Is there any common breakdown or problem with this machine that can produce this apparent death? Any comment or help would be appreciated!!! Thank you very much! Jorge------------------ P.S.: Sorry for my weak english...

Re: *Unused* HP-21 apparently dead - Please help! Message #2 Posted by David Smith on 3 Mar 2004, 9:13 p.m., in response to message #1 by Jorge It could very well be a chip has died (almost always the ACT chip). One thing you NEVER want to do is connect the machine to the charger without a GOOD battery pack installed and making GOOD contact. The charger can easily over voltage the machine without the battery in place. Very often the battery contacts will not mate to the machine contacts. Try placing small wads of aluminium foil between the battery contacts and the machine contacts.

Re: *Unused* HP-21 apparently dead - Please help! Message #3 Posted by Victor Koechli on 4 Mar 2004, 4:12 a.m., in response to message #2 by David Smith Leave it turned on for some time to allow it to warm up, the turn it off and on again. Some woodstocks will not function correctly until after a warming up period. Can take anything from a few minutes to an hour. Cheers, an good luck, Victor

Re: *Unused* HP-21 apparently dead - Please help! Message #4 Posted by Jorge on 4 Mar 2004, 5:56 a.m., in response to message #3 by Victor Koechli Hey, thank you for your recommendations, guys! Victor: I'm going to try that just now. I'll post the results tomorrow. Jorge---------------------

Re: *Unused* HP-21 apparently dead - Please help! Message #5 Posted by Jorge on 4 Mar 2004, 11:03 a.m., in response to message #4 by Jorge The "warm up" option didn't work... :-(

Re: *Unused* HP-21 apparently dead - Please help! Message #6 Posted by Alain Jacques on 5 Mar 2004, 6:18 a.m., in response to message #2 by David Smith Hello Jorge, I assume you have followed David's pertinent advices ... it is a pity if it has not cured the problem. The 21 is quite sensitive to polarity inversion, so please be cautious about rebuilding a battery pack. If the calculator has been turned on recently, the problem is probably not an aging capacitor. The 21 innards are made of 3 boards (keyboard, logic and LED display) interconnected by rows of pins. It may be a bad contact. It is rather easy to cleanly open the calculator by removing the battery pack and the four screws underneath the rubber feet; the top of the shell will then open, the remaining plastic clamp on the bottom will offer some more resistance. Be cautious not to bend the pins and not to fry the electronics with a static discharge. Regards, Alain email me? ... remove §ąN&oSPłAM from the usual stuff

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