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Nelno

Hi-Tek 373-70229A Keyboard Disassembly

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On 1/7/2021 at 8:56 PM, Ed in SoDak said:

Excellent work! It could give a second life to a lot of TI keyboards.

Thanks. I have a 4K resin (SLA) printer on the way that, supposedly, will print with an accuracy down to 0.01 mm. Even though I've got the PETG ones working well, they still need a bit of sanding. I am hoping with the SLA printer I will be able to simply print them and be done without any sanding.

I was able to also fabricate the copper contacts used for each key to replace the one that I broke.

 

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I purchased a 0.15 mm thick copper roll and basically cut these pieces out with a tin snipper and bent them into the shape of the one original that I removed without breaking it. I actually received 0.25 mm copper roll, but it worked perfectly well. The original contacts are 0.16mm thick and that is extremely hard to source. I only found it one place after hours of searching, but I went with 0.15 mm that had a somewhat sooner arrival time (still took about a month to get here).

 

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Attached are some pictures of the contacts. Probably the most useful is the profile pics that show how the contacts need to be bent to actually work correctly (touching when the key is depressed and separated when it is not).

You can see from the pictures that I didn't bother with the tabs on the outside, or the retaining clip that is punched in the middle of the original. I couldn't find any way to reproduce the clip with the tools I have, and I tried the tabs but accidentally cut them off. My tin snips are very unwieldy.

 

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I don't think this will be a problem, however, once I solder the copper strips in. The clip really only keeps the strips secure when the solder is removed, but it doesn't prevent them from wiggling around like the solder does. The tabs on the side just prevent the copper strip from going too deep, but the same can be achieved by careful sizing of the part and the notch that is cut on the bottom to make the solder pin.

To be really useful I need to figure out a way to reproduce these with more precision, though I would recommend not breaking them as the best solution. :) My current thinking is to make a 3D model of a form that can be printed, then the copper strips can be bent to conform to that. Another possibility would be to make a 3D model of the contacts, make a mold from that and then poor in molten copper to make the contacts.

 

Edited by Nelno

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