16 May
2007
16 May
'07
9:15 p.m.
Hi all,
my first VAX ever - died, unfortunately. During the last months, I experi=
enced that the CPU just got stuck at some time, but I could not reproduce=
this error.=20
Sometimes, it froze during or directly after the initialisation procedure=
, or later on after half an hour or an hour of work with VMS.
A friend of mine thought of instable voltages caused by the power supply,=
so I swapped it with another one in order to check, if the supply was to=
blame.=20
Have you actually _measured_ the power supply voltages? Or for that
matter checked the ACLO/DCLO (Power OK) signals that I assume are
genereated by the power supply.
[...]
And now, since last week, the CPU doesn't come up
at all anymore. After s=
witching on the power supply, the seven segment display shows an "F",=20
If this is like other DEC machines (PDP11s and VAXen), all bits of the
LED output port are effectively set in hardware on a reset (giving you
the 'F'). The processor then writes other values to said port. Given that
you never get aything but the 'F', it would appear tht the processor
isn't doing anything. But that doesn't necessarily mean one of the custom
chiops has failed.
[..]
Needless to say that these boards can't be
repaired. As far as I know, no=
schematics were ever published and these big chips on the board are horr=
ible to unsolder and solder, even
if spare ones could be obtained (supposed that one knows, where the "pro=
blem is").
If it is a custom chip that's died, then (de)soldering it is the easy
part of the repair ;-)
But before you assume that, I really would check all the power supply
voltages. And amke sure the ACLO/DCLO signals aren't atuck asserted. Can
you trace out bits of the CPU board circuit to identify the clock source
and reast? If so, it'd be worth checking those next.
-tony