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Vintage Computers Any vintage computer systems, calculators, video games etc., but with an emphasis on 1980s and earlier equipment.

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Old 20th Jan 2022, 2:22 pm   #1
JohnJones
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Default Repairing an original KIM-1 keyboard

Hello All

I've recently got myself an original KIM-1 a Commodore-branded Rev G.

All is well, except the keyboard is unreliable.

The keys get progressively more unreliable and unresponsive from the top row to the bottom.

However, if I press down (quite firmly) below the bottom row then, all the keys on the keyboard seem to work (although the RS key works but never 'clicks' when pressed). I've attached a photo to make it clear what I mean by pressing down below the bottom row.

I'm guessing the keys have become unresponsive with repeated use and that when pressed the contacts under the keys are not made, but that pressing down hard below the last row brings everything closer together and then the contacts are made on a keypress.

It seems obvious to me to dismantle the keyboard, find out what is going on inside, and try to bring the contacts back closer together. I assume the keyboard will come apart if I undo the screws below it on the reverse side of the motherboard (photo attached).

However, before I do, I wanted to see if anyone has ever done so, and, if so, are there any things (especially problems) I should be aware of? I've looked around online and on YouTube and can't find any examples at all of someone dismantling a KIM-1 keyboard.

Any feedback, advice, warnings, etc, would be gratefully received.

Thanks

John
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Old 20th Jan 2022, 3:46 pm   #2
SiriusHardware
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Default Re: Repairing an original KIM-1 keyboard

I have no specific knowledge of the system - which looks lovely by the way, great find - but, when you exert pressure on the lower edge of the keypad bezel does that make the screw heads on the underside of the PCB protrude further out, away from the PCB?

We have a legacy product here where the physical spacing between the buttons, the bits that the user presses, and the switches, which the buttons press down on, is critical. Too far apart, the buttons can't press the switches. Too close together, the buttons press on the switches all the time. It's a balancing act.

I'm wondering if there is a bed of springs maintaining the separation distance between your buttons and the underlying switches. Loosen the screws, the gap gets bigger, tighten the screws, the gap gets smaller, and if you tighten them too much one or more of the keys will be permanently pressed.

You could try just turning the lower 4 screws a half turn or full turn clockwise to see if that makes the lower keys work more reliably. If they won't turn, ie, are already fully tight, then the answer must lie elsewhere.
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Old 21st Jan 2022, 5:50 pm   #3
JohnJones
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Default Re: Repairing an original KIM-1 keyboard

Many thanks for the suggestions.
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Old 21st Jan 2022, 6:44 pm   #4
circuitryboy
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Default Re: Repairing an original KIM-1 keyboard

Was the problem solved?
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Old 22nd Jan 2022, 9:53 pm   #5
JohnJones
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Default Re: Repairing an original KIM-1 keyboard

Quote:
Originally Posted by circuitryboy View Post
Was the problem solved?
I'm collecting very useful advice from people before I start.

I'll update when I've done so.
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Old 23rd Jan 2022, 8:07 am   #6
circuitryboy
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Default Re: Repairing an original KIM-1 keyboard

John and I have PMed about this and I've given some photos of a (more complex) Commodore keypad.
I believe all Comm mid-70's calculators have similar construction so provide the pics here for info.
A possible complication for the KIM-1 is the 15 solder connections at the top of the keypad. If solder has crept between any 'kissing' plated-throughs it would be extremely difficult to separate the boards.
I believe the keypad could be dismantled with its pcb still soldered in place.
Attached Files
File Type: zip kepad 1.zip (3.49 MB, 16 views)
File Type: zip keypad 2.zip (3.99 MB, 12 views)
File Type: zip keypad 3.zip (2.34 MB, 14 views)
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Old 26th Jan 2022, 10:53 am   #7
SiriusHardware
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Default Re: Repairing an original KIM-1 keyboard

If John's keypad is like that then maybe the screws holding the keypad sandwich together have just come a bit loose towards the lower end. Worst case scenario is that the insides of the plastic posts have stripped, and the screws will no longer tighten up.

The keys themselves are one of the nicest retro types around, they look to me as though the legends are actually inset plastic which would make them very hard wearing.
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Old 28th Jan 2022, 12:33 am   #8
circuitryboy
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Default Re: Repairing an original KIM-1 keyboard

I acquired a batch of defunct calculators BITD. Most had the keypad I've shown, with green fluorescent display.
I used several when I needed a quick prototype keypad.
I've now dug deep to find the exact model (rebranded for a German chain store).
While doing that I discovered Commodore/CBM keypads of a different (earlier?) construction.
So include that here for info.
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Old 30th Jan 2022, 7:43 pm   #9
Slothie
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Default Re: Repairing an original KIM-1 keyboard

The keys look very like the keys on the Commodore 796M calculator I used ot have, which I beleive is the rubber membrane type, so I'd imagine Sirius's suggestion might be the case.

And yes, the legends on Commodore calculators of that era were moulded into the keys. Later ones with multifunction keys had printed aluminised labels like the PET chicklet keyboard.
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Old 26th Mar 2022, 6:41 am   #10
circuitryboy
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Default Re: Repairing an original KIM-1 keyboard

Was there a successful outcome for this?
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