How do I open an HP-45?


I bought an HP-45 at a garage sale for two dollars. I inserted a good battery pack from my inventory and the display wouldn't come on. I connected a charger and the calculator works. I looked in the charger connector and saw that the spring switches that are supposed to connect the left and right terminals when a charger isn't connected aren't making contact. I tried to take the back off the calculator to see if I could repair the spring switches. I removed the screws in the battery compartment and the screws under the feet but can't get the cover off. Something near the center of the calculator seems to be holding the cover to the calculator body How do I do get the cover off?

Another question: Can I damage an HP-45 if I connect a charger without a battery pack in place?


There are two other screws under the back label. I don't know exactly where but comparing with my HP-35 I'd guess it's close to the the TTs in LOW BATTERY in the upper left corner and above the 'T' in FUNCTION in the upper right corner. Some people detach the back label and other people drill it to access the screws. It appears the first method is better (mine has been drilled which means it was serviced at least once).

About the second question, the answer is no by what I know, but you should wait for other replies.

Best regards,



Oops! and two other screws under the bottom rubber feet.

Edited: 23 Mar 2006, 9:10 p.m.


You're right with the positions of the screws. I too think that it is a bad idea to drill through the label as it can be detached from the back cover easily (with some patience). If you warm up the label with a hair dryer, the label can be peeled of. When I did this, I made a bad mistake: I peeled just to the position of the screws but no further. Unfortunately, my screw driver touched the label and bent it a little thus leaving a kink in it:(. Anyway, thats still better than to have holes in it!

I have no answer to the second question. When I got my -45, I already had a self-made replacement battery pack at hand. They are easy to make if you find two thin brass plates that can be angled like the original contact stripes (I can make a picture of it if you need it).


Edited: 24 Mar 2006, 3:17 a.m.


Oops! and two other screws under the bottom rubber feet.

Ah, I forgot one important thing: That feet can be lifted from the _outside_ to access the screws, no need to take them off!



The HP35/45/55/70 can work just fine on the charger alone. This should not be done for the HP65 and is very iffy for the HP67.

Many chargers have a bad main electrolytic filter capacitor. It should be replaced whenever you service a new machine.


Thanks to all for identifying the screws under the label.

Next question: Has anyone tried to repair the spring switches in the charger connector, say by bending them. My experience with other hardware such as the battery connectors is that once the springs have been improperly bent there is no real chance of returning them to original stiffness.


Yes, you can bend the charger strap. Try not to overdo it. One thing you should do is clean it well and also the charger pins. Often invisible gunk is the cause of a lot of problems. I use some 2000 grit sandpaper and tweezers. I also treat the pins and strap with some Caig Gold Pen or Deoxit Pen fluid.

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