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28075Re: vintage SRAMs self healing

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  • corey986
    Nov 12, 2012
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      Bill,

      I'm seeing this also. At first I thought it was heat related but as Mike said it appears not. I know I am testing the chips individually using Mike's 2102 RAM tester setup for the Apple II SuperProto board on my II plus. I am pretty sure Mike is doing the same on his Apple II.

      All the 2102 NOS chips I "tested" before installing worked great, but I have an IMS 8K SRAM card that was populated already and after tracking down two bad chips, I decided to start testing them all outside of the system and off the card using the Mike's test setup. That was when I noticed the problem as well. When I first got my MITS 4k card I had some bad ram also, I'm wondering if those chips would have healed if I tested them a few cycles before I threw them out.

      Cheers,
      Corey

      --- In midatlanticretro@yahoogroups.com, "B. Degnan" <billdeg@...> wrote:
      >
      >
      >
      > -------- Original Message --------
      > > From: "Mike" <mike@...>
      > > Sent: Monday, November 12, 2012 3:29 PM
      > > To: midatlanticretro@yahoogroups.com
      > > Subject: [midatlanticretro] vintage SRAMs self healing
      > >
      > > Hi,
      > >
      > > I have been testing some vintage Fairchild 2102 SRAMs and have found that
      > a small percentage of chips that initially fail a pretty comprehensive
      > memory test. However after several reruns of the test, sometimes over
      > several sessions, they all eventually start to pass, and can no longer be
      > made to fail. This is not due to temperature, since in some cases the
      > parts are left for days between test runs. It appears that usage alone is
      > what what causes the chips to "heal". Note that the timing margins of the
      > test setup are extremely generous, so I doubt that the errors would be
      > associated with access speed, changing. Signal quality, power and ground
      > look very good.
      > >
      > > I'm not all that familiar with old SRAM technology, any ideas on what may
      > be going on with these chips?
      > >
      > > regards,
      > > Mike W.
      >
      >
      > My guess is that the chips are OK, it's the socket or contacts of the chips
      > in the socket. The heat loosens up the crud and then until you remove the
      > socket they'll be OK. If you deOxit the chips first, you may have a better
      > initial success rate?
      > bd
      >
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