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25060Re: [midatlanticretro] Re: FD 1771 - Floppy Drive Controller TAX?

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  • Dave McGuire
    Apr 4, 2012
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      On 04/04/2012 10:12 AM, Bill Sudbrink wrote:
      > Ok, here are a couple of weird things that have "bit" me
      > in the past:
      >
      > Cracked pins. I have had TI pins crack in such a way that
      > they looked good in place, would test good with a probe but
      > were bad during a run. I've seen two kinds of cracks.
      > Warning, bad ASCII art follows:
      >
      >
      > | | <-1
      > | |
      > \ /
      > \ /
      > || <-2
      > ||
      > \/
      >
      > I have seen cracks at position 1, right where the pin makes
      > the bend to go into the chip body. Straight across the bend
      > on a soldered chip. Almost invisible to the naked eye.
      > Pressure from a probe on top of the pin closed the crack and
      > made the pin look good under test.
      >
      > I have seen cracks at position 2, at the bottom of the taper
      > where the pin narrows to its insertion width. I have seen this
      > in both soldered and socketed chips. In the socketed case, I
      > stupidly didn't notice the missing piece of pin through several
      > removal/insertions. Under test, it can behave just as above,
      > with the pressure on the pin closing the circuit.

      I've seen this failure mode as well. In one case, microscopic
      examination revealed that the only thing holding the pin together was
      the thin layer of oxide. That was a serious pain to track down.

      -Dave


      --
      Dave McGuire, AK4HZ
      New Kensington, PA
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