hp97 red light


I've seen several hp97's on ebay in non-working order, the sellers say it powers up but only a red light turns on, not the numbers on the display. One also mentions a humming noise.
Does anyone know what error/damage this means, and is it easily fixed?



This is normally a sign of too low voltage. Most probably, the recharchable battery pack is dead (internally short circuited). The humming sound comes from the overloading charger.

Disconnect the charger immediately and replace the battery cell! If the seller or previous owner has "experimented" with the calculator in this condition, there is a good chance, that the charger or some circuits inside the calcultor have suffered permanent damage.

Greetings, Max

Important: Do NOT connect the HP-97 to the charger without a (good!) battery pack in place.


O.K., so better not bid on one of those then.



> O.K., so better not bid on one of those then. Thanks!

Well, as long as you don't bid too much, you can always give it a try. If you are lucky, you get a wonderful machine (the HP-97 is one of my top-5 favourite calculators...) for the additional price of 4 replacement NiCd cells and 30 minutes soldiring work.

Greetings, Max


The humming sound is probably the printer motor running in a machine with a bad gear. This can also lead to the blank display... the machine is waiting for the printer head to return home.

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