ADDS ASCII Restoration

User avatar
TheInverseKey

28 Aug 2018, 01:18

I got this board about a month ago and I noticed that this can be converted to AT and easily with some help from a reddit user u/sexzual_hotdog. He said that if all of the jumpers on the board were in the JP1-4 slots then the chip would run in AT mode rather than ADDS protocol.

So with this in mind I found another user that had a bit of an issue with an NCR 4950. And after some comparison I noticed that this is the same board as the ADDS ASCII and that they were just rebadge. Link to that thread below:

keyboards-f2/help-adapting-the-ncr-4950-t19421.html

Next was to get all off the caps and have a look at the state of the plate..... And that is where all of the work really began. Below is some of pictures of the controller, PCB and rust damage.

Controller and switchable protocols:
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Jumpers and other ICs:
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PCB model numbers 2020/4950/4940
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Rust not the rust:
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After getting the keyboard working with a teensy it is time to get desoldering! I will link all of the documentationf for getting the board working later on. After removing all of the switches the pcb was in quite a rough shape.

Rough PCB:
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I got the PCB a bit cleaner with isopropyl alcohol and a paper towel. Next is to take the plate and remove the rust with a long bath in vinegar. After I painted the plate with Rustoleum and put a matte clear coat for the last 2 layers. After I resoldered all of the switches and started pulling out the sliders to be lubed.(Video of how to do this will be linked later)

Painted plate and opened switches:
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Glued the teensy into the bottom of the case I know I used a teensy 2++ but it had defects that I wouldn't want to use it in another project.

Teensy:
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Reassembled switches and case:
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Caps installed on the board:
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Converter

I just used Soarer's converter for the hex file on the teensy. Some of the key are a bit weird and might need to be remapped and will be doing that in the future. Otherwise it works fine and this is the hardware pinout for the converter.

Top
6 = reset - red
5 = data - green
4 = case gnd - black shielded
3 = clock - yellow
2 = sg gnd - black shielded
1 = vcc +5v - white
Bottom

Top is the original cable and the bottom is the teensy cables:
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Thanks for having a look!

User avatar
Sangdrax

30 Aug 2018, 03:39

That's really clever. How did they figure out the jumper deal, comparing known AT and non-AT versions of the board?

User avatar
TheInverseKey

30 Aug 2018, 03:47

Sangdrax wrote: That's really clever. How did they figure out the jumper deal, comparing known AT and non-AT versions of the board?
On the pcb in the first photo it states how to wire the board for AT.
Last edited by TheInverseKey on 22 Sep 2018, 17:58, edited 1 time in total.

User avatar
Sangdrax

30 Aug 2018, 03:57

"PC/AT Jumper 1-4"

Can't believe I missed that. Now that's cool.

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