HP Forums

Full Version: HP 45 input voltage requirements
You're currently viewing a stripped down version of our content. View the full version with proper formatting.

I have been asked to trouble shoot my friends HP 45, because I have a lot of calculators myself. I don't have much electronic expertise or tools.

The calculator worked for years, operated on the AC adaptor with no battery pack installed. It has quit working, and I thought I might figure out if it would work on batteries alone, by connecting some to approximate the original battery pack. If it worked, then I'd know the adaptor wasn't. The battery contacts don't seem to be marked with regard to polarity. The adaptor does have an input voltage switch and is rated at 0.8W (I think, it is not with me at this moment).

Any suggestions are appreciated.



Hi Bill. The ac adapter for the classic series (35,45,65,67,etc) actually puts out two DC signals: a 5.4 v signal to power the machine, and a constant current signal (which will read about 16vdc with no load) to charge the battery pack. This of course means that the AC adaptor contains rectifier circuitry. I've heard that the smoothing capacitors in the rectifier can go out which results in excessive ripple voltage, which can cause erratic operation of the calculator.

The bottom battery contact is positive one. Note that you'll need to have the adaptor disconnected from the calc to power it from the battery contacts. Also be sure that those little spring loaded plates in the adapter recepticle are making contact with the two outside pins, shorting them together (this is how battery power is routed to the calculator when the adapter is not connected).

Hopefully it's just a bad adapter...
Best regards, Hal

Hopefully this is just the information I need to find that the 45 itself is OK. Thank you very much.