HP12C with a "funny" ENTER key


One of the calculators I bought to replace my stolen ones, is a 12C. It's made in USA, serial no. 2906A05016. It's in near mint condition, when I acquired it it had a leaky battery, but I managed to clean everything before any damage was made.
It works very well, the display is clear, and all the keys behave as expected *except* for the ENTER key.
This key works, but its "action" is weird. All the other keys, when pressed, move down about 3mm before reaching the bottom; and only after about 2mm of travel you feel the dome collapsing. They feel quite "soft" at first, then they feel "firmer" just before the dome collapses.
This ENTER key instead, only goes down about 1mm. It doesn't feel "sloppy", and when at rest it's at the same height than the other keys (or possibly a fraction of mm higher). But it feels "firm" from the beginning of the movement; you need more force to get it moving than the other keys. And as soon as it moves, the dome immediately clicks. It almost feels like the dome is already "almost-collapsed" when at rest. As if there's something wedged between the dome and the pin pushing on it. I tried "wiggling" the key around to try dislodging any extraneous material, but nothing happened.

Now, the question: does this description tell something to anyone? What might have happened? And, what should I do, considering that opening a 12C isn't trivial? Should I keep it as it is, or open it to get it to work as intended (if I can)? I intend to use this machine, do you think that using it as it is now could lead to premature failure of that key (though at that age, it might not be defined "premature" anyway)?



Ciao Christian,

compared to the HP-48G you mentioned earlier, opening an old HP-12C *is* trivial. As easy as unfastening four screws ... d8-)


compared to the HP-48G you mentioned earlier, opening an old HP-12C *is* trivial. As easy as unfastening four screws ... d8-)

Well, not really... The four screws don't get you to the keyboard mechanism, to get there you also have to remove 40 heat-stakes! :) And what worries me isn't removing them, but finding a way to put everything back together solidly enough...



Sounds like a perfectly normal Voyager keyboard to me.

The Enter key behavior is different because the dimension from the hinge point to the point of contact is approximately three times longer than all other keys. It will not have the same "feel" and "click" as the others due to it having:

  1. A longer lever
  2. A larger area of finger contact when pressed
  3. A larger contact area under the key that presses on the dome

This photo shows the differences from the back of the keys view:

Edited: 6 Mar 2011, 9:48 a.m. after one or more responses were posted


Sounds like a perfectly normal Voyager keyboard to me.

Randy, I don't know, I also have a new (the VERY fast model) 12C, and it doesn't show this behaviour. Of course you can feel that the ENTER key is a bit different, but it still moves down the same distance as the others when pressed. And the "click" comes after a couple of millimetres of travel, while on the "old" 12C it comes immediately. And you don't get a good tactile feedback at all. Can you confirm that the new and the old 12Cs present a substantially different behaviour? Of course I don't want to open it if that's how it's supposed to be! :)


This is a topic that comes up at least twice a year - that is someone buys an older Voyager and thinks there is something wrong with the Enter key. What you've described is exactly how it should be as there is nothing wrong with the unit.

The later models made in China use different domes and materials between the keys. They might look the same from the outside but that's where the similarities end. Comparisons should be cosmetic only because the only thing in common between the units from a hardware standpoint are physical dimensions.

Edited: 5 Mar 2011, 5:54 p.m.


What you've described is exactly how it should be as there is nothing wrong with the unit.

Well, that's great then... if that's how it's supposed to be, I'll stop worrying! This is my first and only "old" Voyager, so I didn't know a thing like that was to be expected.

On a "side", partly off-topic, track: I seem to have problems with the search function. If I enter some words in the search field, selecting "Last several eons" as time frame, and then click on the "view message index" button at the bottom... it only shows me results from the last few days. I'm surely missing something obvious, but I just can't find a way to make a search including old messages...



Not that Randy's info needs any external support, but all my 1980s vintage Voyagers behave *exactly* as he describes.


When using the ENTER key, push it near the upper end. It works much better that way.

As Randy described, the geometry makes it feel very different from the other keys, especially if you push it at the bottom.

Edited: 9 Mar 2011, 11:40 a.m.


The Enter key behavior is different because the dimension from the hinge point to the point of contact is approximately three times longer than all other keys.

While there is limited mechanical real estate to balance
out the top and bottom actuation force of the voyager
enter key, it is somewhat perplexing why the bottom matrix
dome couldn't have been used as an identical parallel key.
Some fudging of the hinge stabilizer would be needed but
the numbness associated with the enter key bottom seems a
little strange.

As it is the lower dome position is stuffed with a snap dome
and generates its own unique keycode if you can find a way
to actuate it. While the upper dome "enter" generates an
8:4, the phantom lower dome is 8:5. Even more interesting
is an 8:5 key code maps to an inverse sin operation by at
least the 15c firmware.


Christian, I've got a "Made in USA" 15c that has an Enter with a feel similar to what you are describing. I'm the original owner and actually sent it to HP after buying it in 1987 and asked them if the Enter key was normal and would they repair or replace it. They replied and basically said that it was within HP's specifications and enjoy your 15c. It has performed flawlessly for 23+ years. I hope that this helps.




Thanks everybody for the replies. Much appreciated. I feel reassured now and I'm looking at my old 12C with different eyes, knowing that it's behaving as intended! :) Now I won't fear that if I use it I will break something inside...



I was intrigued by the discussion of the different feel of the ENTER key on the 12C. I have ten Voyagers: three 11C's, six 12C's (all made in the USA), and one 16C, but sadly no 15C. I verified the different feel on all of the devices and that the feel can vary somewhat depending where I press on the key. Then I encountered some really bad news. My 11C S/N 2217A03623 which has the bug also has a problem with the ENTER key such that pressing the key near the bottom of the keyboard causes the ENTER operation to take place but without any tactile feel.

While I was playing with the keyboards I eventually noticed that the top of the ON key on each unit is somewhat lower than all of the other keys even though the feel is the same. I wondered what that was about, so, following the old adage, I looked in the manuals. I found the following footnote on page 16 of the 12C manual

Note that the ON key is lower than the other keys to help prevent its being pressed inadvertently.

A similar note appears on page 16 of the 16C manual. If there is a similar note in the 11C manual I couldn't find it.

The same feature is on my 10B's,17BII, 32S and 48S. Interesting!

While I am on the subject of the ENTER key I have one question, namely, why is the ENTER key a different size on most HP machines?


...why is the ENTER key a different size on most HP machines?

It's what HP users had come to expect, ever since the HP-35. Biggest gripe about the otherwise stellar 50g is no big Enter key.


At least you don't have to hunt for it with it being the lower right most key though ... I'm kind of use to that being the + key.


...why is the ENTER key a different size on most HP machines?

A good reason for ENTER being the largest key is because it is activated for any general set of calculations more any other key, including any of the / * - + keys.

A related question is why the ENTER key is not positioned in the same column of keys as the / * - + keys on most HPs made in the past 30 years, as it always was on pre-Voyager HPs. Also, these keys were always on the left side of the keyboard.

The Voyager layout required upsetting the classic pattern, with / * - + keys moved to the right, no longer aligned below the ENTER key. For unknown reasons HP has continued placing for most post-Voyager models the / * - + keys on the right, while returning the ENTER to its traditional place on the left. Having the ENTER key on the side opposite the / * - + keys creates the worst possible arrangement, and it surprises me to see it continued on the otherwise excellent recent HP 30b.

Most users are right-handed. A logical arrangement for such users is (1) having the ENTER and / * - + keys all on the *right* side of the keyboard, and (2) having a large ENTER key ABOVE the / * - + keys. The HP 49/50 series violates all of criterion (2), but at least it represents a shift in the right direction. :-)

Edited: 9 Mar 2011, 6:45 p.m.

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