One working 33C out of two?



I have come across a 33c which is apparently willing to function - except that the keys do not respond (minor detail...)

On the other hand, I have a 31e with fuctional keyboard but battery contact and display problems.

I'm thinking of some surgery. Is there any chance to sucessfully adapt the 31 keyboard contacts onto the 33? I've not opened anything yet - waiting for expert advice.

TIA - best regards, Daniel CLEMENT


If none of the keys work, chances are that the problem is not with the keyboard contacts, but with the calculator electronics, so swapping the keyboard will not work.

Also, keep in mind that there were at least two versions of HP-3x series calculators out there, in one of which the chips are actually soldered onto the keyboard "sandwich" assembly. There may also be other differences between the 31E and the 33C keyboard circuit layout.

By the way, many 3x-series problems are simply due to the pressure contacts used in these machines, so it is possible that you may be able to restore both to good working order with a simple disassembly and thorough cleaning of these contacts.




another mayor problem with the 30 series is corrosion on the battery contacts and/or the charger plug slider contacts.
The latter is worse.
I have a *brand new in box* 33C, where the batteries were in the calc for twenty years.
The result is corroded mainboard:-(

If someone knows a method to open these calcs w/o scratching the plastics,
please let me know.


BTW: the 34C I have for sale doesn't have any corrosion;-)


Well, corrosion is of a problem in any calculator with NiCd cells. But you're right, for some reason these 30-series machines seem to be more prone to it than others. I once received a 33E that was stored in its case for years with a set of partially dead batteries inside. When I opened it, there was white crystalline stuff (potassium carbonate, probably), tons of it, even on the outside! The flexible cable connecting the battery contacts to the power supply PCB easily rots, too.

The only other machines I've seen that are as prone to corrosion are TI's third generation scientifics, like the TI-55 and the like, with the BP-7 electronic battery packs. In those, battery packs, the circuitry tends to rot away completely.

As for opening a 30-series machine, until today I'd have been one of those suggesting that you really need to pull the case apart with force. (Worked for me so far without breakage.) However, I just read a post here that suggests that it is possible to slide the case apart after all, without applying excessive force. I'll give it a try.



Opening the HP3x series without excessive force is probably my post. Yes, it certainly works, or at least
it has done on all the HP3x machines I've had to open up. It still takes considerable force to get the
case to unlatch, but it doesn't feel as though you're about to crack the back cover in half....
The same applies to the Woodstocks (HP2x) series, by the way. The easiest way
to take those apart is to take out the battery pack, take off the top 2 feet, undo the
screws under them and then press on the charger pins until they're
just clear of the bottom case (white part). Then slide the bottom case down slightly wrt the keyboard until the front edge comes clear. Then
slide it back up so that the battery contacts will fit through the case. It takes longer to explain how to do it than to actually do it when you get the knack.
And it certainly seems to be 'kinder' to the machine.

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