Repair HP35

I have a 1973 HP 35 that only works if the power switch is pressed down while in the on position. I'm sure that it can be easily fixed if the unit is opened up. It has never been opened and the back placard is near perfect. From a collectability standpoint, is it better to leave as is or repaired?


Easy fix, hard part is removing the label.

Check out this link and scroll down for an explanation for the label removal

HP 45

And this link by Mark Hoskins:

Label removal


Edited: 17 Nov 2012, 5:53 p.m.


It might be worth a try to drop a bit of anti-corrosion spray into the switch (without opening) and moving the slider a couple of dozen times.


I would agree with Frank as a first prelim non invasive attempt. However, the grease used for the slide switches is prone to dirt collecting and drying into a hard paste.

It would require a solvent to thin which may damage the plastics if the case. Also the problem would just come back.

This is a classic problem with the 'classics'. Greasy dirty waxy build up between the slide and the keyboard contact.

Cheers, Geoff

Take look at the switch mechanism for the HP 45 int the first link. Scroll down the pictures until you find it. This calc exhibited exactly the same symptoms yours does.


Even worse, it might be corrosion beyond repair - both the switch slider and the PCB are gold plated, which might wear off after intensive use and is ultimately non-repairable. But don't assume the worst for now ;)


Thanks for the ideas. I'm afraid that attempting the label removal may leave me a mangled, melted mess. I am thinking about just cutting away the label over the screw holes.

I don't plan on this being a regularly used calculator, I have an 11c for that. Will probably sell the 35 in the future, but don't want to kill any value it may have if a collector sees the holes as a negative.


You may get more for it umangled with a known problem if you are planning to sell.


Don't punch holes in the label! If you really don't want to remove the label, which will not melt (aluminum with contact cement) then follow Franks suggestion by introducing some plastic safe contact cleaner into the switch,

Use an eye dropper and follow up by cycling the switch. Repeat a few times. If it is not destroyed contacts and just gummy residue then it should loosen and function.

Cheers, Geoff

If you have a hair dryer, heat up both corners of the top of the label. While still hot, NOT MELTING HOT :-) insert a fine pocket knife blade under the corner and lift the corner gently to expose the screw heads. (2cm). Don't fold the label back just slowly lift it by the corner applying heat as necessary. Once the screws are exposed you are in.

Just push the corners down again. At least at this point if you do sell it the label can be made to look perfect again by the next owner.


So I followed Geoff's link to his fix. It was actually not too bad. I did get the back bit too hot as the case bowed slightly from pulling the label off. Removed the boards, cleaned the switch and lubed it with a dab of silicone grease. Cleaned all the keys and their contacts. Before putting it back together I gently re-heated the back case and flattened the label area. Re-installed the label and I'd say it is 95% as good as before. Certainly better than poking holes in the label. Thanks for the advice!




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