5 Nov
1998
5 Nov
'98
7:34 a.m.
Date: Tue, 3 Nov 1998 21:28:22 +0000 (GMT)
From: ard(a)p850ug1.demon.co.uk (Tony Duell)
To: classiccmp(a)u.washington.edu
Subject: Re: PDP11 training troubleshooting
Message-ID: <m0zao01-000IyTC@p850ug1>
Content-Type: text
You know, I've made some nasty comments about Field Service in the past
(what DEC enthusiast hasn't...), but now I realise it wasn't all their
fault. I mean, not being able to pull boards is terrible...
Yeah, but it taught you to think microcode, block diagram and
real troubleshooting instead of pul and swap.
I was a board swapper in the Field, but it made me an informed and
logical board swapper.
Hmmm..
This actually wouldn't have worked for me, if I'd been allowed to
do what I liked to the machine.
Well, the class wasn't 8-(...
God gave us extender boards (and DEC made extender boards) so you could
run a CPU module outside the case to look at internal signals. It's a
standard way of figuring it all out. Trying to debug an 11/45 only being
able to look at backplane signals is horrible...
Sure. Tell the customer he/she will be down an extra hour while
you extend the board to find the fault, desolder the chip
and replace the 10 cent bus driver. Nope. Swapping was reality in the field
when I was there. Board level (early 80's DEC) was (unfortunately)
replaced with shotgunning and option swap out by many in the late 80's.
Were you give (or allowed) a KM11 maintenance card?
For those who've not
seen one, it's a board (acutally 2 boards...) that you stick in special
slot in some DEC machines. It's got 28 lights and 4 switches on it. In
the 11/45 it'll let you single-step the microcode (or even the clock
sequencer), display flag signals, etc. You can get the uPC on the panel,
of course.
They were used in the 11/70 class, the RK05 maint class and a couple of
others. The 11 new hire used the 11/34's built in programmer panel
for much the same stuff.
However, in
the real world I'm more likely to start with a 'lucky dip'.
Unplug all connectors/boards, clean contacts, look for bent pins. Check
all fuses. Power up and check the power rails with a voltmeter.
with machines under maintenance most folks keep
their hands out of
them. (except for printers and terminals) This means something broke.
Hmmm... OK, pity the poor field servoid who used to deal with the VAXen
at one of the Universities I was at. He knew that there were DEC hackers
there - people who read printsets for fun. The system manager was one
such, and I joined in the fun.
Typically, we'd call out field service with a call of the form 'Oh, it's
gone again, and this time bring DEC part # <whatever>'. We'd already had
the thing apart you see, and knew what we were doing. DEC didn't seem to
mind too much - they'd bring the bit, do a few tests to confirm, and
install it. Check power and work from there.
Oh, indeed. And ACLO/DCLO. Those cause more problems that you'd believe.
Especially on H742 power supplies where C3 (I think) on the power control
board goes open. ACLO and DCLO then get mains frequency ripple on them,
and the rest is obvious.
-tony