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30078Re: IMSAI 8080

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  • DanielB
    Apr 3, 2013
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      --- In midatlanticretro@yahoogroups.com, joshbensadon <no_reply@...> wrote:
      > Hi Daniel,
      > > I seem to have it running small programs ok now, but it looks like I have a problem with the 8212 latch on the front panel that is used to drive the LEDs that can be written to on IO port FF. All the input signals look ok, even checked the timing with a logic analyzer, but I still get no output to the LEDs. I am guessing that is no an easy chip to get a replacement for.
      > >
      > I saw all the answers regarding 8212 availability. I bought 6 of them from ebay for $3 each. Sounds like you have things well under control, capturing the timing signals, etc. I just want to state the obvious (which at times may get over looked). The LED's are tied to VCC, so they light with logic 0. But I'm sure you have that all figured out and are on the right track by replacing the 8212.
      > What's your next step? Disk Drives? EPROM? Toggle switches get a little tedious. Actually they get a lot tedious in a short time.
      > :)J

      Yeah, I even went as far as grounding the resistors to the LEDs to be sure they light, and they did, so it looks like it's the 8212.

      I have a Technical Design Systems system monitor board that I want to get running next, but I am waiting for my order of replacement tantalums to come in before I proceed on that. I also have a disk controller that I have not been able to find any documentation on so I am in the process of tracing out the circuit for that board and I will probably dump the EPROM to see figure out how it's software works.
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