26 May
2004
26 May
'04
11:19 a.m.
I have a PDP-11 here that I'd ike to power on but there's
What model?
no power switch that I can locate.
The power supply is a H750 and the A/C entry panel is a BC05t
with two separate lower power three pin connectors on it.
I pinned them both out as:
+33V, external red wire
0V, external white wire
gnd,external green wire
This sounds like the DEC power control bus. Don't assume the colour code
is 'normal' -- in particular, don't assume that green is chassis ground.
The 3 pins are common (0V), on/, and off/, Connecting on/ to common will
energise a contactor in the power control unit and apply mains to the
units in the rack. Disconnecting it will turn it off again (there is no
latching).
Connecting off/ to common will turn the system off, even if on/ is also
connected to common (i.e. off/ has priority).
Conventioally, the power switch (maybe a key-lock switch on the CPU
panel) connects on/ to common. Thermal switches, to detect overheating,
connect off/ to common.
They're the same shape&size connectors as the
four
pin 5v/12v ones used everywhere today.
Figured that two of these wires could go to an "on" switch but thought
it would be better to ask than to just go around shorting things to see
what happened.
You will do no harm by shorting these wires together in any combination.
-tony