Author Topic: Splicing an old keyboard  (Read 1612 times)

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Offline mikeymac17

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Splicing an old keyboard
« on: Sun, 24 October 2010, 23:45:15 »
I found an old omnikey keyboard that seems to have white alps. Problem is the connector has been cut off. The board has LED's for the num lock, caps lock, and the scroll lock. The wires at the business end are grey, brown, red, yellow. Is there any hope for rescuing this amazing keyboard? I am willing to solder and I have access to usb plugs or ps/2 plugs.

Any help will be greatly appreciated.

Offline didjamatic

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Splicing an old keyboard
« Reply #1 on: Mon, 25 October 2010, 00:21:09 »
Which model?  Are the dip switches on the back edge or under a trap door on front?

Pics would help too
IBM F :: IBM M :: Northgate :: Cherry G80 :: Realforce :: DAS 4

Online Findecanor

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Splicing an old keyboard
« Reply #2 on: Mon, 25 October 2010, 05:07:03 »
There is no standard for the colours on the wires. I have seen completely different colours in different AT and PS/2 cables.
If you have the original cable, then you could repair it by soldering by colour and insulating using heat-shrink tubing.

Otherwise, you will have to follow the wire to the soldering pads on the circuit board and figure out which type of signal goes to which soldering pad. If you are lucky, this will be marked on the circuit board.
Otherwise, hopefully someone on this board has an identical keyboard and could test the wires on his board and help you with that.

If you are unlucky, then the only option is trial and error. With four wires, there are up to 4! = 24 different combinations to try.
However, you could make a calculated guess about which wire goes to "ground": it is often tapped in more places than any other signal line. On many circuit boards, the "ground" signal is also wider than all others. If you find "ground" then there are only 3! = 6 combinations left to test.
That is how I figured out how to connected my Dolch keyboard (it had a "RJ plug"): I got it right on the third attempt.
If you have to do this, then I suggest that you use an internal connector, so that you don't have to de/re/solder on each attempt.
"Normal is the greatest enemy in regard to creating the new. To get around this you have to understand normal not as reality but as just a construct." -- Alan Kay
Daily driver: Phantom (Lubed Cherry MX Clear, Lasered Cherry PBT keycaps with Row A. Plastic "Frankencase". Custom firmware, Swedish layout)

Offline mikeymac17

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Splicing an old keyboard
« Reply #3 on: Mon, 25 October 2010, 07:32:02 »
And that is what I assumed. But is it possible to convert an AT keyboard to either ps2 or usb?

Offline Fwiffo

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Splicing an old keyboard
« Reply #4 on: Mon, 25 October 2010, 08:54:18 »
Should be; there are AT to PS/2 adapters, at the very least.
You can call me... Keyboard Otaku... or not quite...

Offline mikeymac17

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Splicing an old keyboard
« Reply #5 on: Mon, 25 October 2010, 09:26:36 »
Popped the case open. There is no Dip switch board. But I found more information, it is an omniey programmable ultra-t/102/101 pcb. Designed by IF-BBC. And it says northgate computers. I will get pictures up when I find a camera.

Online Findecanor

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Splicing an old keyboard
« Reply #6 on: Mon, 25 October 2010, 14:06:26 »
Did you find any text near where the cable was attached?
"Normal is the greatest enemy in regard to creating the new. To get around this you have to understand normal not as reality but as just a construct." -- Alan Kay
Daily driver: Phantom (Lubed Cherry MX Clear, Lasered Cherry PBT keycaps with Row A. Plastic "Frankencase". Custom firmware, Swedish layout)

Offline sixty

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Splicing an old keyboard
« Reply #7 on: Mon, 25 October 2010, 14:21:02 »
Quote from: ripster;238372
I'm always suspicious of cut off cables, sometimes techs would do that to nonfunctioning keyboards.  Worth a try though.


I have received a bunch of Cherry keyboards from a source, all of them had their cables cut. The reason for this was simply that it was too much trouble to properly unwrap all the cables out of the chaotic cable soup at the office. It seems they did the same to all the printers and monitors :eek:

Offline JohnElliott

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Splicing an old keyboard
« Reply #8 on: Mon, 25 October 2010, 14:34:27 »
If you've got a multimeter and you can identify what sort of chip the controller is, you can see which of the leads in the cable have zero resistance to the +5v and ground pins on the controller. That gives you those two, and then you're just left with two ways round to try the other two for Data and Clock.

Offline kps

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Splicing an old keyboard
« Reply #9 on: Mon, 25 October 2010, 15:55:38 »
Quote from: JohnElliott;238549
If you've got a multimeter and you can identify what sort of chip the controller is, you can see which of the leads in the cable have zero resistance to the +5v and ground pins on the controller. That gives you those two, and then you're just left with two ways round to try the other two for Data and Clock.


Dollars to donuts it's an 8051-family controller, and at most a double-sided PCB, so you  can just follow the traces by eye.