I have been busy.
I have completed the keyboard.
Building an OSI 542 Rev C Keyboard
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- Location: British Columbia, Canada
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- Posts: 370
- Joined: Fri Mar 07, 2014 4:44 am
- Location: British Columbia, Canada
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Re: Building an OSI 542 Rev C Keyboard
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
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
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- Posts: 370
- Joined: Fri Mar 07, 2014 4:44 am
- Location: British Columbia, Canada
Re: Building an OSI 542 Rev C Keyboard
Not yet tested.
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- Joined: Fri Mar 07, 2014 4:44 am
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Re: Building an OSI 542 Rev C Keyboard
I finally got around to testing the completed keyboard and it works (Mostly)!
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.
I am not familiar with how the circuit works, so I am asking the online experts here what to check next.
/Jeff
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.
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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- Joined: Fri Mar 07, 2014 4:44 am
- Location: British Columbia, Canada
Re: Building an OSI 542 Rev C Keyboard
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.
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.
Here is a Note File that describes the fix. 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.
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.
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.
Here is a Note File that describes the fix. 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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- Joined: Fri Mar 07, 2014 4:44 am
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Re: Building an OSI 542 Rev C Keyboard
One final note... the MX keys feel awesome!
/J
/J
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Re: Building an OSI 542 Rev C Keyboard
Jeff -
Thanks for posting the fix. I ran into the same problem with a continuous reset and found that a 4.7K resistor across the .001uf cap let the circuit work - but clearly this was not the proper repair.
- Gary
Thanks for posting the fix. I ran into the same problem with a continuous reset and found that a 4.7K resistor across the .001uf cap let the circuit work - but clearly this was not the proper repair.
- Gary
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Re: Building an OSI 542 Rev C Keyboard
Here is my Parts List. I use the spreadsheet to track my build progress.
/Jeff
/Jeff
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Re: Building an OSI 542 Rev C Keyboard
Thanks for the assembled keyboard Jeff!
I was using the Parts Layout.pdf at the beginning of this post for parts placement and D1-D4 are shown reversed. I should have used your Keyboard Part List.pdf pic as they are show correct.
Thanks again,
Keith
I was using the Parts Layout.pdf at the beginning of this post for parts placement and D1-D4 are shown reversed. I should have used your Keyboard Part List.pdf pic as they are show correct.
Thanks again,
Keith