HP-97 wihtout battery pack?


May I use my HP-97 without a battery pack, just with the power supply? I would like to youse it as my desctop calculator. I know that the Woodstock serie will be damaged just with power supply, but what about the HP-97?
I do not have a spare battery pack.


I would not branch it w/o battery pack. As minimal safety messure I would just use a big electrolytic capacitor.



It is safe to use the 97 without a battery pack (there is a special circuit intended to prevent the incoming voltage exceeding the Vss rail), but you won't be able to use the printer or card reader (which take too much current for the HP mains adapter).

This circuit is present in all Topcat models, but it only works when the machine is on. For this reason, if you are lucky enough to have an HP95C, do _NOT_ connect it to the adapter without a good battery pack in the machine. You can easily damage the CMOS RAM chips (same as in some Woodstocks IIRC), and maybe other chips. If you kill the ROMs in a 95C you're in big trouble. This is based on reading the schematics for all said machines...


I don't dare to do it on my 97 but many years ago I killed my 25 by putting a capacitor in place of the battery pack and plug the charger in. Without the cap the display would flicker but after installing the battery it was fine. The cap raise the voltage higher and killed the calc.


Never operate the 97 w/o battery. the printer will be destroyed the first time you try to use it. The circuits may work until a spike comes through.


fwiw, if you can find original pack and/or get it re-built - just use a 4xAA Nicad flat pack with stranded wires, loop it around the 2 contacts in the battery compartment and then fill the empty space around the battery with some sponge foam - works pretty well.

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