HP Forum Archive 14

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Sinking keys in HP Classics Message #1 Posted by Bo on 18 Oct 2004, 10:41 p.m. Hi, Many (most?) HP Classics appear to have the “sinking keys” flaw to a lesser or larger degree. By sinking keys I mean that the individual keys sink down into their openings. It does not affect all keys to the same degree, as the central keys, e.g. 7, 8, CHS, EEX sink the most, whereas the keys in the upper, lower, left- and right-most rows sink less. It appears that the contact board below the keys flexes downwards in a concave fashion – like an old and used bed. Although the keys sink on all models, it is more apparent on the models with the larger keys, e.g. a HP-67. The sinking keys do not impair contact function, however, it makes the keys rattle, it makes gabs between the keys and the keyboard which collect dirt, and it looks “stupid” – at least to me. HP quality? The above appears not to be related to use as this flaw sometimes can be seen to a small degree in much worn examples whereas mint, hardly used examples can have keys sitting pretty deep. So what is going on? Did the calculators originally all come with the keys in the correct place, or was this flaw created during assembly, e.g. the planar (I assume) contact boards being flexed when mounted in the calculator housing? Or did the contact board flex with age? Does anyone know the answer to the above or have some theory as to what is going on? Also, would it be possible to fix the problem when taking a given calculator apart or is something permanently out of shape?

Re: Sinking keys in HP Classics Message #2 Posted by Randy on 19 Oct 2004, 7:15 a.m., in response to message #1 by Bo The flexing metal key strip has fractured. This is common in heavily used units. They can be repaired with strips from another unit. I've never seen any other reason for a key to be lower than others around it on a classic. The keyboard PCB is made rigid by the back plate of the calculator which forms the battery box. The PCB cannot bow unless the 6 to 8 screws holding the back plate in place are striped or missing.

Re: Sinking keys in HP Classics Message #3 Posted by Vassilis Prevelakis on 19 Oct 2004, 12:39 p.m., in response to message #2 by Randy So how do you attach the replacement strip? **vp

Re: Sinking keys in HP Classics Message #4 Posted by David Smith on 19 Oct 2004, 3:40 p.m., in response to message #3 by Vassilis Prevelakis Attach with solder.

Re: Sinking keys in HP Classics Message #5 Posted by Bo on 19 Oct 2004, 12:57 p.m., in response to message #2 by Randy I don't think broken strips are the reason to "my" problem. This would mean that most strips should brake on hardly used calculators, very unlikely. Also, it wouldn't explain the keys sinking in a concave manner.

Re: Sinking keys in HP Classics Message #6 Posted by Randy on 19 Oct 2004, 7:01 p.m., in response to message #1 by Bo I re-read your original post. You mention "classics" several times. To me, the only classics are the early LED machines: 35,45,55,65,67,70,80. Are you confining your discussion to those machines or does classic to you mean something different? As for your "hardly used" units, I've seen absolutely pristine 67's with several fractured strips. Let's get real - most of these machines are 30 years old. I've never seen a key with a bow in the keytop. Any chance you could post some photos? Edited: 19 Oct 2004, 7:04 p.m.

Re: Sinking keys in HP Classics Message #7 Posted by Wayne Brown on 20 Oct 2004, 12:35 p.m., in response to message #6 by Randy Quote: I've never seen a key with a bow in the keytop. By "the keys sinking in a concave manner" I think he means the keys near the edges of the keyboard are the highest, and get progressively lower as you move to the center of the keyboard from any direction -- as if the bottom of the keyboard were bowl-shaped.

Re: Sinking keys in HP Classics Message #8 Posted by Bo on 22 Oct 2004, 12:15 a.m., in response to message #7 by Wayne Brown Yes, that is exactly what I mean - and what I wrote. By "Classic" I refer to what is called classic on this site: HP-35, 80 etc. As to an example, see e.g. the hpmuseum's HP-67 at http://www.hpmuseum.org/3qs/673q.jpg Even this pristine example has the flaw I am talking about: the 7, 8, CHS and EEX keys clearly sit very deep and are tilted rearwardly, just take a look at the side surfaces of the keys and compare with the other keys in the same row. Still, I can't believe that all the contact strips broke on hardly used examples whereas they didn't breake on some very used examples. BR, Bo

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