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Thread: apple II Plus keyboard encoder problem

  1. #1
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    Default apple II Plus keyboard encoder problem

    So I dont know how I missed this but I guess I spoke too soon when I said I finally got my Apple II plus up and running. I just got my cffa3000 card in the mail and tried running it when I realized none of my shift keys were working at all. Now I did have to replace 3 alps key switches on this keyboard so I didnt know if the problem was mechanical or a bad IC on the encoder.
    Luckily someone just gave me another Apple II plus recently, and its keyboard is fine.
    I first tried the entire keyboard from the good apple II into the suspect machine. IT worked fine. I then swapped the encoder card from the good system to the suspect keyboard. The keyboard works fine! So I know its not the keys themselves, its something on the encoder board:IMG_20180611_134600778.jpg in the photo the top board is bad and the good one is on the bottom with a couple spots of whiteout (so I would know which is which)

    you can see they are slightly different boards.. So what do I do? How do I repair this bad encoder board? Any tests I can run on it?

    Thanks

  2. #2
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    There is a 74LS04 logic chip, I tested it and its good so thats not the culprit.

  3. #3
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    How are they different? One has a GI AY-5-3600 encoder; the other has the SMC KR3600 clone.

    You might want to drop a line to Sean to ask about his PIC replacement for the 3600

  4. #4
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    Thanks Chuck, I sent Sean an email.

  5. #5
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    ok this is weird. I swapped the 3600 IC's. No change! I put the suspect IC on the known good encoder board and the shift keys work. I put the known good 3600 IC on the suspect board and it still doesnt have shift keys. ITs got to be something else on that encoder board.

  6. #6
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    Try replacing the 74LS00 at B3. See the schematic on PDF page 217 in Winston Gayler's book

  7. #7
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    Chuck tested both 74ls00, they are both OK.

  8. #8
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    So, next question--is the KR3600 getting the right signal from the LS00? Should be pretty easy to tell.

    How about the outputs (and jumpers) on pins 6-10 on the KR3600? This isn't rocket science.

  9. #9
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    well right after testing the 74ls00 logic chips I sockected them and cleaned the header pins from the encoder board. I decided to try the keyboard out again and its now working fine. So I dont know, dirty pin, bad solder joint. Cant tell but its working.

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