5 Jul
2025
5 Jul
'25
12:33 p.m.
On Jul 5, 2025, at 8:05 AM, Jon Elson via cctalk
<cctalk(a)classiccmp.org> wrote:
On 7/4/25 14:32, Mark Kahrs via cctalk wrote:
My story is about a 750. Under maintenance it ran for some time until the
tape drive failed. Tech installs new controller board, fixed.
Then the CPU fails. New CPU, fixed.
Then the tape drive failed again. New board, fixed.
And so on through various peripherals, disks, tty’s, etc.
Eventually they send out a guy who sits with it for a day, poking and prodding just
about everywhere for a while. At the end of the day says that he’ll be back tomorrow
with the correct part.
The correct part: A new backplane.
Took the entire day to remove/replace the hardware, and lo - the machine never failed
after that.
David
"Nature doesn't care how smart you are. You can still be wrong." - Richard
Feynman
David Barto
barto(a)kdbarto.org
Jon Elson's take hits home. A 780 was
delivered and VMS was running. We
installed 4.1BSD and it ran fine until it crashed. Field service insisted
we needed a full set of RS-232 wires in our cable. Still crashed
(surprise!). Switched to VMS, still crashed after a while. Local field
service couldn't find it. The big guns flew in from Maynard. First day:
Couldn't find it. Second day: "What, what's that wire doing there? Have a
wire-wrap tool?". Removed wire from backplane. Boots, runs. Engineer
flies home.
Holy cow, HOW did he find it!!?? The KA780 backplane was a HUGE mass of wires!
Jon