DEC 872-A power controller docs?

Chris Elmquist chrise at
Mon Mar 21 10:34:50 CDT 2011

On Sunday (03/20/2011 at 07:44PM +0000), Tony Duell wrote:
> All power cotnollers after a certain date (early 1970s, IIRC) use the 
> same 'power control bus', os the manual and/or printset for any of them 
> would be a good start.
> >From what I rememebr, the 3 pins are ground, ground-for-on, and
> ground-for off, 'off' taking priority over 'on' if both are grouded. 
> There is no lartching in the power controllers.
> You interconnect all the power controllrs in the system with 
> straight-through cables. The power swtich on the CPU box is connected 
> betweem the ground and ground-fro-on wires, so that turning this on 
> acrviates all the controllers and powers up everythjing. Over-temperature 
> swtiches and the like are connected betweem ground and ground-for-off, so 
> thatr if any device overheats, the whole system shuts down.
> Thes signals are not TTL level. They may be up to 24V, nd you may have to 
> sink enough currnet to operate a reed relay. Just in case you want to 
> design your own swithcing units...

Thanks Tony.  I plan to put a rocker switch between ground and
ground-for-on and use that to power up my entire "corporate" rack.

Someone has already cut a square hole in the bottom front kick plate
of this rack and so I was looking for something to fill that hole--
plastic plugs, body putty, and then a nice rocker switch came to mind.

With that I won't have to crawl behind the rack to power it all up...
and so this will connect nicely to one of the Power Control Bus connectors
with just two wires and fill the void (so to speak) that someone put in
this panel.


Chris Elmquist

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