H750 (PDP-11) power on?

From: Tony Duell <ard_at_p850ug1.demon.co.uk>
Date: Wed May 26 18:19:42 2004

>
> 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
Received on Wed May 26 2004 - 18:19:42 BST