hp calculators

ARGH! Do not do that! The AC adapter for the 67 ahs 2 outputs. One is a constant voltage output (about 4.2V I thinK) the other is a constant-current ouptut (55mA) with a maximum voltage of 15V or so. In the machines without card readers that use this adapter (35,45,55,70,80), the battery is disconencted from the machine when you plug the adapter in,. The constnat current charges the NiCd, the constant voltage runs the logic. These are safe to use without a battery pack fitted In the machiens with card readers (65, 67), the card reader amplidier/motor driver chip is conencted directly across the battery pack. If theree's no battery fitted (or the battery is opne-circuit), this chip gets 15V across it. The user manual for the HP65 warns that this can do damage. The chip was redesgned for the 67, and the new version is supposed ot stand up to this, but I am not going to risk it. Incidentally, if you have a 20 series, 30 series or 90 series with continuous memory (19C, 25C, 29C, 33C, 34C, 38C, 95C), you _will_ do damage if you conenct the AC adpater without a good battery installed. The battery acts as a shunt regualtor in these machines, and the RAM is powered by the battery at all times (that's how the ocntinuos memory is maintained). Without the battery, the RAM sees abotu 12V when the charger is plugged in and it doens't much like it, The safest way to charge the batteries is outside the calculator. HP sold 'reserve power packs' -- battery charger units -- for the classic (35, 67 etc), Woodstock (20 series), Spice (30 series) and Topcat (90 seires) amchines. I've never seen one for the Sting (10, 19C) machines, though. The classic-seires one is not too hard to find, the Topcat one a little harder, The Woodstock one is quite rare, the Spice one rare enough that some people claim it never existed (I can assure you it does). Incidentally, if ytou can't find one closer, I should be able ot find you a dead NiCd pack for your 67. -tony