Building an OSI 542 Rev C Keyboard

Jeff
Posts: 330
Joined: Fri Mar 07, 2014 4:44 am
Location: British Columbia, Canada

Re: Building an OSI 542 Rev C Keyboard

Post by Jeff » Sun Mar 31, 2019 3:53 am

I have been busy.
E4A22242-2DC8-4B96-ACEF-A87795A4512D.jpeg
E4A22242-2DC8-4B96-ACEF-A87795A4512D.jpeg (1.87 MiB) Viewed 1143 times
I have completed the keyboard.
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Jeff
Posts: 330
Joined: Fri Mar 07, 2014 4:44 am
Location: British Columbia, Canada

Re: Building an OSI 542 Rev C Keyboard

Post by Jeff » Sun Mar 31, 2019 4:10 am

gekaufman wrote:
Thu Nov 08, 2018 7:54 pm
Finished up the keyboard last night - Hopefully will have time to test this weekend, and anxiously awaiting the Keycaps.

- Gary
Gary, post some pics of your finished keyboard 😃
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Klyball
Posts: 195
Joined: Tue Dec 09, 2014 12:53 am

Re: Building an OSI 542 Rev C Keyboard

Post by Klyball » Sun Mar 31, 2019 10:42 pm

Does it work?
Replica 600 Rev D:8K,CEGMON
Replica 610 Rev B: 24k,MPI B-51 with Custom Data separator D-13
510 on the bench/replica 582 backplane/replica 470a /replica 555/original 570B/2 x Shugart 851
Ongoing : 630 ,620 ,510,542c,custom 590,SA1200,592,594,596,598

Jeff
Posts: 330
Joined: Fri Mar 07, 2014 4:44 am
Location: British Columbia, Canada

Re: Building an OSI 542 Rev C Keyboard

Post by Jeff » Mon Apr 01, 2019 12:58 am

Not yet tested. 🤪
Image

Jeff
Posts: 330
Joined: Fri Mar 07, 2014 4:44 am
Location: British Columbia, Canada

Re: Building an OSI 542 Rev C Keyboard

Post by Jeff » Sun Aug 25, 2019 4:03 pm

I finally got around to testing the completed keyboard and it works (Mostly)!
Keyboard.jpg
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What does not work is the BREAK/RESET circuit. While it DOES automatically reset the system upon power up, it does NOT STOP resetting the system! I put my scope on the Reset wire that goes to the 502 and confirmed the pulse.
Reset Pulse.jpg
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I am not familiar with how the circuit works, so I am asking the online experts here what to check next.

/Jeff
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Jeff
Posts: 330
Joined: Fri Mar 07, 2014 4:44 am
Location: British Columbia, Canada

Re: Building an OSI 542 Rev C Keyboard

Post by Jeff » Sun Aug 25, 2019 6:45 pm

I found the problem with the Break key circuit. There is an incorrect trace on the PCB.

I solved it by lifting pin 8 of U1H and then connecting +5V to the U1H pin 8 OF THE SOCKET, not the lifted pin.

I can see how this happened. When Grant was laying out the PCB based on photos I sent him, I sent him a diagram incorrectly showed the trace going to pin 8. I incorrectly assumed that the power would go to opposite corners as is traditional.

Here is the photo I provided to Grant a few years back... I added the orange line today to show the trace under the socket.
Original.png
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The 74LS75 breaks from tradition of placing the power and ground on opposite corners of the chip.
+5V is designated on Pin 5 and Gnd is on Pin 12.
74LS75.jpg
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Here is a Note File that describes the fix.
PCB IMPORTANT NOTE.pdf
(309.37 KiB) Downloaded 26 times
And now my keyboard is working perfectly!
/Jeff

EDIT: Originally, I thought Grant made the mistake on the incorrect trace. I came across a photo of a diagram that I sent to him with the mistake clearly made by me. I have edited the above to reflect this new info.
Last edited by Jeff on Sat Sep 14, 2019 5:33 pm, edited 1 time in total.
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Jeff
Posts: 330
Joined: Fri Mar 07, 2014 4:44 am
Location: British Columbia, Canada

Re: Building an OSI 542 Rev C Keyboard

Post by Jeff » Sun Aug 25, 2019 6:46 pm

One final note... the MX keys feel awesome!

/J
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