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30064Re: IMSAI 8080

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  • DanielB
    Apr 2, 2013
      --- In midatlanticretro@yahoogroups.com, joshbensadon <no_reply@...> wrote:
      > --- In midatlanticretro@yahoogroups.com, "DanielB" <danlb_2000@> wrote:
      > <big snip>
      > > Finally made some more progress on the IMSAI. The problem with the Examine switch ended up being a bad 74107 JK Flip Flop on the front panel. I also replaced some of the caps on the one-shots on the front panel. So the examine and deposit seem to be working ok now, but I am still having some flaky behavior, but I am making progress.
      > >
      > Great catch on fixing the FP. BTW, do you need a shematic for it?
      > I had a number of issues, some were bad connections between IC's and sockets. Always a good idea to extract each IC, examine it's leads for tarnish (use an eraser or some harsher method to clean the leads). Reseat the chips in the sockets, sometimes I wiggle the chip in and out a little to help break down the tarnish inside the socket.
      > Also, I had lots of issues with bad S-100 edge card connectors. For these, only scrub them with a polymer eraser. A big issue I had was BAD or Flaky RAM. Drove me nuts, because some of my RAM actually looked like it was working, but later testing revealed "issues".
      > Leave no stone unturned, you'll have a stable system soon enough.
      > :)J

      Thanks for the input. Neither my front panel nor CPU board (except the Z80 add-on) are socketed so no issue with tarnished pins, but I will have to check that on the other boards.

      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.
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