Image Map Image Map
Page 9 of 9 FirstFirst ... 56789
Results 81 to 85 of 85

Thread: Quest COSMAC ELF

  1. #81
    Join Date
    Jun 2012
    Location
    UK - Worcester
    Posts
    1,631

    Default

    It is only a changeover contact button, a couple of inverters acting as a debounce circuit and a diode - so I would chase it through with your logic probe or multimeter. There must be an obvious fault somewhere. Unless someone has swapped the inverters for non inverters in the debounce circuit - but that would cause problems elsewhere you would have thought...

    Dave

  2. #82
    Join Date
    Jan 2011
    Location
    Vancouver, BC
    Posts
    2,558
    Blog Entries
    1

    Default

    I received my replacement 4508s today and am pleased to report a replacement chip solved the problem. So I guess a bad 4508 can pull up the wrong bit and cause the machine to think a switch is triggered when it's not. I entered in a few programs including the one that makes the QLED blink indefinitely and they worked without a hitch. The only weird one is the one that detects the pressing of the INPUT.. that still does the opposite of what the program expects. I'm going to chase that one but I'm reluctant to mess with it too much since the basic entering and running of programs is ok.

    I will say I *hate* these 3 position switches. Both for having 3 positions and their short poles. The other ELF is much nicer to work on. It's also a bit disorienting with the LEDs rather than the segmented displays.. have to eseentially convert to binary twice in my head to make sure I've entered and that the computer has stored it right. On the three position note - I found out by accident that the middle position counts as 'ON' to the computer.

    Thanks so much for everyone's help. Most appreciated. Especially Dave!!

    Stay tuned for next week.. I've bought yet another beast..

  3. #83
    Join Date
    Jun 2012
    Location
    UK - Worcester
    Posts
    1,631

    Default

    No problem.

    Great to see another card back to life (almost).

    The 3-position switches didn't sound a great addition by the original constructor anyhow - and how right we were!

    Dave

  4. #84
    Join Date
    Jan 2011
    Location
    Vancouver, BC
    Posts
    2,558
    Blog Entries
    1

    Default

    Just FYI: I tried out the example program for the PROM. Worked just fine.. counted up on the LEDs just like it was supposed to. Nice!

  5. #85
    Join Date
    Jun 2012
    Location
    UK - Worcester
    Posts
    1,631

    Default

    That unit is interesting. I had never seen an ELF with a PROM before. Thanks for sharing.

    I obtained a copy of the PROM for myself - I may build one over the Christmas period if I get time (which I never will - but I can dream can't I?!)

    Dave

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •