Stearns Computer keyboard low profile Linear Micro Switch

Anakey

23 Jul 2021, 17:30

Recently picked up this board based on a photo provided by the ebay seller that it may have Micro Switch SC because of having a spring in the switch stem. This spring is not present on the rubber dome verients and the keycaps have the same font and style as used in the ITT Courier 1700 where the SC switches were found. Not much about the system remains online, obviously it did not sell well, though bearing in mind that they were against the might of IBM it is not suprising. There is a digital archived scan of Creative Computing that did a review of the complete system http://archive.org/details/creativecomp ... ew=theater The following images were taken after the keyboard had been disassembled and cleaned.
First-min.png
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Second.png
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As you can see with the rear legs folded up, the keyboard does have a very slim profile especially when this was made in 1984. This made it possible to store the keyboard under the main machine when not in use.
Third.png
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The keyboard has a solid steel base plate anong with 2 flip out feet at the back. There was originally 4 small cork feet, only one was on the board when it arrived and fell off when cleaning due to the age. Replacement cork feet have been ordered and should arrive soon.
Fourth-min.png
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With the base plate removed it is possible to see that the pcb, normally mounted above the keyboard assembily, instead is placed below, this helps reduce the large forehead that was common to have at the time and also enabled the low profile. The aluminium backplate holds the membranes in place thanks to metal tabs that go through the plate and are then twisted to hold the assembily together.
Fourth p2.png
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MicroSwitch date stamp showing 6th week 1984
fifth.png
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The inside of the top case shows the date stamp and also a stamp from the manufacturer. The plastic and finish are very similar to taht of a model F, having a very similar texture and still pure white with no yellowing.
Sixth.png
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Keyboard assemble outside the casing. Notice the red spots on teh keycaps, these are for in switch LEDs. There are also blanking plates to offer support to the case between the main keyboard and numpad.
Seventh-min.png
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as you can see the bottom plate has slots for the tabs punched through but also had a round raised lip around each hole to keep the membranes aligned.
Eight-min.png
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Top of memberane, the graphite pads that connect to the in swith LEDs are visible
nine-min.png
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The plates on the bottom of the switch are similar in design to the clicky version on the Courier 1700 however the central spring is split. The ends of the spring have hooks that go inside the coil spring. when the coil spring is pushed against the 2 halves it causes them to flex, pushing on the membrane to activate the connection. Dummy switch on the spacebar
eleven.png
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Switchplate without keycaps showing in switch LEDs

Now lets take a look at the switches in detail. I have used a switch with LED for the closeups.
Switch-top.png
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Switch-top 2.png
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Switch-led detail.png
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switch-bottom.png
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The LED is held in a socket. This socket could be swapped to the other diagonal side.
dummy-top.png
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dummy-bottom.png
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Dummy spacebar switch.
Blanking plate top.png
Blanking plate top.png (488.36 KiB) Viewed 1100 times
blanking plate bottom.png
blanking plate bottom.png (660.59 KiB) Viewed 1100 times
Blanking plate.

Anakey

24 Jul 2021, 23:14

I got the new cork pads so now it is fully complete.
last.png
last.png (3.84 MiB) Viewed 1034 times

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