Have used this technique in the past, but only if the fault does not kill some of your replaced boards. Much prefer logical diagnosis, if only for theMessage 1 of 1 , Oct 7, 2008View SourceHave used this technique in the past, but only if the fault does not kill some of your replaced boards.Much prefer logical diagnosis, if only for the knowledge that you can beat the machine, but tempus dictates the method.Mike----- Original Message -----From: Ray SillsSent: Tuesday, October 07, 2008 3:00 PMSubject: [personal] Re: [midatlanticretro] OT Humor
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
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
> systems developed a problem which was quickly narrowed down to a
> module of
> 20 pluggable units. Rather than taking the time to logically figure
> which PU was at fault, the tech replaced half of the PUs and re-ran
> 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
> I don't particularly agree with this technique, but if time is
> and you have the spares I suppose it makes sense.
> Mike Loewen mloewen@cpumagic. scol.pa.us
> Old Technology http://sturgeon. css.psu.edu/ ~mloewen/ Oldtech/
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