Strange problem with HP-22
#1

When I switch on the calculator, sometimes it has a blank display, or a full line of periods. After a few minutes, all the display segments flicker. Sometimes, when I press a key, I get a single flickering "8.", but nothing else happens. Nothing actually works.

Could this be caused, or related, to the ACT chip? This has been known to be a problem in "Woodstock" (HP-21, HP-22, HP-27) calculators. Or is it something else?

I have been using two slightly-used alkaline AA cells for the battery - but not the AC adapter. (One was not included with this used calculator.) I don't think the extra (3.0 vs 2.5) voltage is causing any trouble.

#2

Hi Blaine,

I fear you are right. I saw exactly the same symptoms in one of my Woodstocks and I was told by several experts here it is the ACT. Usually this happens when someone uses the AC adaptor while old or no cells are in. Since you seldom know the status of your rechargeable cells exactly, it is highly recommended to load the cells outside the calculator.

Extra battery voltage from your fresh alkalines does not harm your Woodstock according to my experience.

#3

This sort of problem is usually a bad battery or connection. The classic bad ACT problem is a display of 00000000 or sometimes a blank display or possibly a single very bright digit lit.

#4

I had a thing like that as well, carefully "resoldering" all the contacts solved the issue for once and all. Use a small tip, taken precautions to static charge and make sure you do make a short circuit.

Success

#5

> This sort of problem is usually a bad battery or connection.

I do use two alkaline AA's in the battery pack, bridged by a rolled-up wad of aluminum foil. The voltage checks out at 3.1, which is more than recommended (but not likely to do any harm.) It's possible that voltage is OK but current low. Or the bad connection could be somewhere inside the calculator.

> The classic bad ACT problem is a display of 00000000 or sometimes a blank display or possibly a single very bright digit lit.

I sometimes get this too, combined with all the flickering. Sometimes when I press a key, I get an "8." by itself, or a "0" or a "@" (backwards 9). So I'm not sure it it's a bad battery, ACT, or both.

#6

It is beginning to sound like a bad ACT, but it could still be a bad connection. I would open up the machine (two screws under the upper two rubber feet) and clean all the circuit board connections with 91%+ isopropyl alcohol. Try and keep the alcohol off the LED window and keyboard face. Also lightly sand the tips of the battery contacts with very fine (600+ grit) sandpaper. A lot of these machines had some hand soldered components in them and the old solder flux (often invisible) seems to be a common problem.

#7

Perhaps it is that stick of dead wood Vlad that is behind this...



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