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Re: Hardware Question Regarding Membership Card

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  • jdrose_8_bit
    The material the bag is made from looks like aluminum foil on a plastic base. I am a bit bummed but it is a good exercise in troubleshooting for me. What were
    Message 1 of 39 , Apr 18, 2013
      The material the bag is made from looks like aluminum foil on a plastic base.

      I am a bit bummed but it is a good exercise in troubleshooting for me.

      "What were you using for a power supply? If it was current limited, the good news is that it's not likely to have damaged anything important."

      No, not electronically current limited. Two AA batteries in series.


      "The Membership Card (and 1802 circuits in general) are fairly easy to troubleshoot. You can slow the clock down, or even stop it completely at any point, and probe things with a multimeter, or even a logic probe that is nothing but an LED and series resistor."

      I was counting on that.


      "A useful logic probe can be built with 3 LEDs and a resistor. Let's say you're running it on a 5v power supply. Connect 1 yellow and two green LEDs all in series (green on the positive end). When connected across the 5v supply, they have a voltage drop of 1.7v + 1.75v + 1.75v = 5.2v, so they will be off (or perhaps just barely glowing). Now connect one end of a 1k to 10k resistor to the junction of the yellow and green LEDs. The other end of this resistor is your logic probe. Connect a piece of wire to it with an alligator clip, or better yet an EZ-hook clip."

      I built a simple logic probe using a red/green LED and an op-amp from a circuit I found online. I like your probe better. Will put one together after I finish writing this.


      "Have you checked the supply voltage? Is it between 3v and 5v? Check to see if the oscillator is running. U4D pin 12 should be high, and U1 pin 39 should be an AC voltage (as indicated on your multimeter. If the clock is running, then put the 1802 in RUN mode, and see if you have an AC voltage on the various 1802 outputs; TPA, TPB, SC0, and MRD. All of them should have an AC voltage (i.e. are cycling high/low) even if the program that is running is utter nonsense. The LEDs may be stuck because of some problem in the output port. If you ignore the 8 LEDs, and toggle in a program to blink Q, does the Q LED then go on and off."

      Thanks for the troubleshooting tips. Appreciated.
    • Lee Hart
      ... Hi jdrose, I saw that Josh Bensadon had offered to fix your MC card, but didn t see any more on how it turned out. Did it get fixed? If not, I would be
      Message 39 of 39 , May 21, 2013
        On 4/18/2013 3:16 PM, jdrose_8_bit wrote:
        > I have a few other SB computers to keep me busy. I also have a second
        > 1802 MC computer as a back-up. I was about to try some INP/OUT
        > experiments that I cannot not do in an emulator when it failed.

        Hi jdrose,

        I saw that Josh Bensadon had offered to fix your MC card, but didn't see
        any more on how it turned out. Did it get fixed? If not, I would be more
        than happy to repair it as well.

        --
        We live in a Newtonian world of Einsteinian physics ruled by
        Frankenstein logic. -- David Russell
        --
        Lee A. Hart, http://www.sunrise-ev.com/LeesEVs.htm
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