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Re: [personal] Re: [midatlanticretro] Re: OT Humor

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  • Mike Hatch
    We had an SDS9300 on critical usage. The system came with a test rack, scopes, sig gens, full circuits, and spares. We could reapir any board without recourse
    Message 1 of 1 , Oct 7, 2008
      We had an SDS9300 on critical usage.
      The system came with a test rack, scopes, sig gens, full circuits, and spares.
      We could reapir any board without recourse to the manufacturer, there was no backup in the UK or Europe.
      A PDP7 we repaired ourselves, PDP11's were on 4 hour response by DEC and a car load of spares.
      ----- Original Message -----
      From: Ray Sills
      Sent: Tuesday, October 07, 2008 3:19 PM
      Subject: [personal] Re: [midatlanticretro] Re: OT Humor

      The assumption is that the replacement modules are known to be good.
      It that's in question, then all bets are off.
      Presumably, in a mission-critical application like SAGE, there would
      be good spares on hand. Some large systems
      have test bench ways to determine operational quality off-line, so
      you'd know that your spare modules are OK.

      But, yes... if the spares are questionable, then the problem is a
      whole lot bigger.

      73 de Ray

      On Oct 7, 2008, at 10:06 AM, fairlanefastback wrote:

      > Whats to say all the replacement modules are free from any defects in
      > such a scenario? One can introduce a new problem unwittingly in such
      > a methodology.
      > --- In midatlanticretro@ yahoogroups. com, Ray Sills <raysills@.. .>
      > wrote:
      >> Hi Mike:
      >> In a certain sense, that method of troubleshooting does optimize the
      >> time it takes to get the unit functional. By "walling-off" half the
      >> possible defective units by replacing them with good modules, you can
      >> quickly determine where the fault lies. Of course, as you way, you
      >> have to have at least 50% spare modules of the total that are known
      >> to
      >> be good. And by replacing half of all the modules, you have a 50-50
      >> chance of getting
      >> the system back up on the first swap.
      >> If the system is still bad after that swap, then the same procedure
      >> will work by swapping out half again of the remaining un-swapped
      >> modules, etc.
      >> It would mean a maximum of 4 swaps to find and replace the bad
      >> module. And since it was a SAGE system, involving national defense,
      >> you'd want to get it back up ASAP. That's the point, of course.
      >> 73 de Ray
      >> On Oct 7, 2008, at 9:16 AM, Mike Loewen wrote:
      >>> On Mon, 6 Oct 2008, Stan Brewer wrote:
      >>>> How did DEC Field Service Engineers change flat tires?
      >>>> They took the spare out and kept swapping out tires until they had
      >>>> 4 good
      >>>> ones on the car! : )
      >>> That reminds me of the first time I was exposed to the "shotgun"
      >>> technique of troubleshooting. It was on the SAGE system, and one of
      >>> the
      >>> systems developed a problem which was quickly narrowed down to a
      >>> module of
      >>> 20 pluggable units. Rather than taking the time to logically figure
      >>> out
      >>> which PU was at fault, the tech replaced half of the PUs and re-ran
      >>> the
      >>> tests. He continued replacing half of the remaining PUs until he
      >>> was left
      >>> with the bad one. He explained that sometimes you don't have time
      >>> to be
      >>> logical, but instead have to get the system back up as soon as
      >>> possible.
      >>> I don't particularly agree with this technique, but if time is
      >>> critical
      >>> and you have the spares I suppose it makes sense.
      >>> Mike Loewen mloewen@...
      >>> Old Technology http://sturgeon. css.psu.edu/ ~mloewen/ Oldtech/
      >>> ------------ --------- --------- ------
      >>> Yahoo! Groups Links
      > ------------ --------- --------- ------
      > Yahoo! Groups Links

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