DEC power control? How do it know?

From: Jay Jaeger <>
Date: Sun Jun 4 17:54:48 2000

On my older systems you also needed "loopback" plugs at each end (at least
I have that on my 11/20, where one of the two connectors on the 11/20 has a
plug connecting pins 2 and 3, and at the far end is a plug connecting pins
1 and 2.

I just did a little test. I checked my Microvax, a BA23. It puts 555 ohms
between pins 1 and 3.
Also, if I short pins 1 and 3 on the BA11K holding my 11/34, (or an H720
power supply), it turns it on.

So, maybe you can try anyway -- probably would not hurt to try running the
3 wire cable between the BA23 (my MicroVAX BA23's have nothing in pin 2, by
the way) and the BA11 (top connector).

As an initial test, you could plug your BA11 in, and connect pin 1 to pin 3
and see if it turns it on.

Of course, you would not get the "Ground for Off" automatic shutdown
capability, but it looks like the BA23 wasn't set up for that anyway, at
least on mine.


At 06:51 PM 6/3/00 +0100, you wrote:
> >
> >
> > Ok, I'm cobbling together a PDP-11 and I ran out of slots on my BA11 so I
> > put a bus extender into it and plugged that into a BA23. The system works
> > fine (thank you micronotes!) but I'd like to figure out how I could set it
> > up so that powering up the 11 powered up both the BA11 and the BA23. Now I
> > know the little 3 plug do-hickey (I think it is a mate-n-lock) normally
> > connects to a power sequencer in the rack, but I don't have one of those.
> > Is there any way to make it work otherwise?
>At one time the DEC power controllers (they're not really sequencers)
>were easy enough to find at radio rallies, etc. They're pretty generic
>(there are no Unibus or Qbus versions :-)), so something like an 861 or
>an 871 would work fine. Have these units now attracted E-overpay prices?
>The other possibility is to make your own power controller. They're not
>that complex. The 3 pins on the connector are :
>The 'truth table' is :
>Ground-for-off Ground-for-on Power controller relay
>Floating Floating Off
>Floating Grounded On
>Grounded Floating Off
>Grounded Grounded Off
>Oh yes, these signals can be at up to 24V, and the supply is sourced by
>the power controller.
>Conventionally, in the CPU box, a contact on the power switch, or a
>transistor in the PSU, is connected between Ground and Ground-for-on.
>Turning on the CPU grounds Ground-for-on and turns on the power
>controller relay. This then powers up the rest of the system.
>Overheat-protection switches are wired between Ground and Ground-for-off.
>If any one of those trips, it turns off every power controller in the system.
>A few mounting boxes (the BA11-K is the most common one) have their own
>built-in mini-power-controller for just that box. If you string the
>3-wire cables between them, set the toggle switch on the back to
>'remote' and plug them all into the mains then turning on the CPU will
>turn on the other boxes. But most mounting boxes don't work like this :-(
>I notice Bob Davis has posted some schematics of a power controller, so I'll
>comment further there.

Jay R. Jaeger The Computer Collection visit
Received on Sun Jun 04 2000 - 17:54:48 BST

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