Side tracking slightly from the "VAX 86x0 schematics" discussion into changing
field service procedures over the years: I remember some fairly hairy cases in
the 1970, when FS engineers had to be way more capable than board swappers.
1. DEC RS64 fixed head disk was behaving badly, making more noise than
expected. Machine was not under contract. FS tech took it apart, diagnosed
bad bearing. To save the customer (college physics department) a pile of
money, he took it to Appleton Electric Motor Co., where they found a suitable
bearing, pulled off the bad one, pressed a replacement on. Jim reinstalled the
motor into the drive, worked great.
2. Same college, different machine: RF11 drive was showing "clock track
failure". Diagnosis: drive is not spinning. Same tech. Jim took the drive
apart on a desk in the computer center, noticed a head had crashed and melted,
hot-glueing itself to the platter so the motor was blocked. This machine was
under warranty, so he ordered a pile of parts: full set of heads, motor,
platter, plus tools. Replaced the motor, replaced all the heads and aligned
them, replaced the platter, and formatted the timing track. The manual for
that formatter was not exactly intellegible...
3. Different university, CDC 6500 mainframe, occasional data corruption in one
of the mass memory transfer paths. After lots of test code added to the
application (PLATO system), the tech concluded he knew the answer. Opened up
one of the cabinets, lifted up a massive bundle of wire to reach a spot where
one of those wires was "punched in" to a module connector, and re-punched the
pins of that wire. Repeat at the other end of that wire. Run tests, problem
fixed.
In that machine, there were a dozen or so chassis, with up to 750 or so
modules, each with 28 signal pins, most of them interconnected to elsewhere
with twisted pair wires terminated in tapered pins that were pressed into
place. It was a surprisingly reliable system but we learned it wasn't 100%,
and it took quite some skill and perseverance to find which of those tens of
thousands of wire connections was the failed one.
paul
