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Restoring/repairing/replacing classic series button contacts
09-15-2019, 01:59 AM
Post: #1
Restoring/repairing/replacing classic series button contacts
Hi!

This is my first post here. I don't know if I'm getting the terminology right here, so please correct me if I'm wrong.

I have an HP-35 with some buttons that are not clicky, but springy. I've opened the calculator and determined that the springy behavior is due to the contacts being broken; the metal pieces have a vertical cut across them, I guess just due to too many presses. The buttons still work but I'd like to restore them to their clicky glory.

What would be the recommended way to restore these, besides buying a second calculator and replacing these pieces?

Thanks!
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09-16-2019, 06:15 AM (This post was last modified: 09-17-2019 05:57 PM by Bernd Grubert.)
Post: #2
RE: Restoring/repairing/replacing classic series button contacts
Hello,
I made the replacement at an HP 11c with metal domes, which I bought from AliExpress. There you will find metal domes with different diameter and force. I chose those with the lowest pressing force. They work well, although they still seem a little bit too stiff. Since they are not very expensive you might give them a try.

Regards
Bernd

Edit: I confused AliExpress with AliBaba.
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09-20-2019, 05:06 AM
Post: #3
RE: Restoring/repairing/replacing classic series button contacts
(09-16-2019 06:15 AM)Bernd Grubert Wrote:  Hello,
I made the replacement at an HP 11c with metal domes, which I bought from AliExpress. There you will find metal domes with different diameter and force. I chose those with the lowest pressing force. They work well, although they still seem a little bit too stiff. Since they are not very expensive you might give them a try.

Regards
Bernd

Edit: I confused AliExpress with AliBaba.

Thank you! I’ll give that a try
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09-24-2019, 01:52 PM (This post was last modified: 09-24-2019 01:53 PM by burkhard.)
Post: #4
RE: Restoring/repairing/replacing classic series button contacts
I think the answer depends on whether you want your calculator just functional or "right".
Since you have it functional now, and are not happy, I'll assume you really seek to get it "right".

While the domes suggested which might have worked well on a Voyager, my guess is that they will probably be too "clicky" for your 35.

When I compare keyboards on my Classic series, I find that the 35 and 45 have decidedly less of a pronounced click throughout the keyboard than the later 55, 65, and 67 (well OK, only a ½-Classic) models. I think it was more subtle on the earlier models than on the later ones. I seem to recall there was a key contact change that eliminated gold-plated contacts to save $, but I'll leave that for the real historians.

So, to get it "right", like it sounds like you want, you are probably going to need to salvage some parts from a trashed donor calculator, preferably another 35 or maybe a 45. Why don't you post a "WANTED" message in the "Classifieds" section of this forum? Someone might have a row or two they will part with cheap or even gratis.
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09-25-2019, 07:00 PM
Post: #5
RE: Restoring/repairing/replacing classic series button contacts
Although even if you get a donor machine, has someone successfully transplanted the strips? I think they are all spot-welded to the circuit board so I’m not sure how easy it is to remove and transplant them successfully.
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09-25-2019, 10:27 PM
Post: #6
RE: Restoring/repairing/replacing classic series button contacts
It can be done, we did for an HP67 and for an HP25
You will need to pull gently a strip (I suggest an entire line) from the donor
Then you can remove the broken parts, in our case we replaced a complete line
of an HP67 and the donor was an HP45
Once cleaned the underneath, we pass the donor with a 2000 grit sand paper and
we solder the donor to the PCB.
Soldering has to be very thin so that it will not make difficult to close the chassis
You can view some pictures here :
https://www.icloud.com/sharedalbum/it-it...TcsmGlo5ca
take care !!

Edoardo & Alberto
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09-25-2019, 10:54 PM
Post: #7
RE: Restoring/repairing/replacing classic series button contacts
(09-25-2019 07:00 PM)[kby] Wrote:  Although even if you get a donor machine, has someone successfully transplanted the strips? I think they are all spot-welded to the circuit board so I’m not sure how easy it is to remove and transplant them successfully.

On the Voyager series, they are not spot-welded. They simply lay (in a row of 5 connected by a common strip of sheet metal) on top of the circuit board. There is a large tape that goes across the whole face of the PCB that holds all of them down.

I'm in the process of writing up how I replaced a damaged LCD module (from a donor 12C) on a 16C, including how I re-used the existing plastic pins to heat-stake the PCB back to the upper with great success. But with such details, it's going to take me some time (weeks maybe). Feel free to ask questions in the meantime.
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