25 Apr
2015
25 Apr
'15
4:58 a.m.
From: Josh Dersch
the power supply was completely dead. I've rebuilt
the supply
Just out of curiousity, what was the failure mode? (Also, trying to figure
out of the failure could have killed things...)
BTW, is it in a BA11-K box, or a BA11-L?
the AC LO and DC LO signals are high (these are active
low, right?)
Yes. All UNIBUS signals are active low _except_ for grants, if memory
serves...
The status register display is dark.
Hmmm.
The system does not respond to any keypresses on the
panel.
Sounds like you've got the variant with the real ("Programmer's") front
panel
- that's a plus. Although it's too bad that variant doesn't have a
"HALT/CONTINUE" switch - it would have been good to power it on with the HALT
on, which would have prevented it from trying to do any bus cycles.
No response to HALT/CRTL, though? Although I'm not sure if it would respond
to that if it was in a double-bus fault loop (NXM on trying to respond to a
NXM).
I've taken it down to a pretty minimal
configuration, sans any memory
or other stuff.
Always wise... :-)
Slot 3: (AB) M9301 (bootstrap terminator) / (CDEF)
M7859 (front panel board)
Most 11/34's run those cards in slot 4, not 3 (probably to leave room for the
FPP/Cache in slot 3), but slots 3 and 3 are (AFAIK) identical, so it should
be OK to run them there.
the NPG jumpers on CB1-CB2 are all present on the
backplane.
Err, I hope that's a typo for "CA1-CB1" - tying CB1 to CB2 (+15V) would not
be good (although if you did do it, it should be harmless in this
configuration).
I don't really have much to add to Don's message, about the next things to
try. There doesn't seem to be a way to configure the M9301 to have the
machine halt on power up, which would to my mind be the ideal. It might be
worth throwing a 'scope probe on MSYN, to see if it's trying to do bus cycles.
Noel