22 Jan
2007
22 Jan
'07
10:54 p.m.
Yes, Tony's replies to some of my questions
here have been extremely
valuable (his explanation of Unibus NPG comes to mind), but I think his
contribution here goes deeper than that.
More than specific diagnostic information, very often what Tony
offers is a diagnostic *mindset*. Information is reasonably easy to
acquire. The capacity to get from here to the desired state with that
information is a lot harder. Rarest of all is the ability to impart
that diagnostic mindset - to show the "student" how to think through any
problem instead of how to fix this particular problem.
Thankl you. That is one of the nicest things anyone has ever said about
me :-)
THere are many reasons why I rarely simply post the answer to a specific
probkem. The first is that often I don't lnow the answer. I can't. It's
impossibe to know what's weong with a machine you've never seen based on
some 'high level' fault description. Sure there may be a common cause of
that fault --a n example on the PDP11/44 is that the '?CP DIDN'T START'
error message is almost always cased by an open grant chain. Notice I
said 'almost always'. There are other possibilities. and if you don't
realise that you'll be 'bitten' one day.
I may not have even seen an example of the machine in question, but I may
have worked on related machines. Hopefully I can give some pointers to
likely areas to look at for the fault, together the owner of said machine
and I can figure out just what is going on.
The second reason is that, like it or not, I am not going to be around
for ever. I could be killed by an omnibus tommorow (either run over by a
Routemaster or electrocuted by the PSU ina PDP8/e). I'd like to ensure
that there will still be poople around who can keep these fine old
computers running. And that means knowning how to do fault tracing.
A thrid reason is that I find some aspects of the hardware of these
machiens to be very beautiful. And I'd like others to experience that
beauty, by understanding the schematics.
So if nobody objects (and FWIW I've receiced not one message that
supports Sellam's view), I'll carry on posting as I've always done.
-tony