PDP-11/34 PSU Yet Again

From: Tony Duell <ard_at_p850ug1.demon.co.uk>
Date: Tue Mar 4 17:56:17 2003

> Well, I finally got around to testing the PSU on my 11/34. I measured at the
> backplane connectors with no backplanes plugged in. Everything checks out
> except for the -5V and +20V. Accordingly, the LED at the bottom of the H745
> brick (regulator 1) does not light. However, some of the other voltages
> coming from the H745 (according to the BA11-K FMPS) seem to be OK.

I thought the H745 provided +20V and -5V only. What other voltage do you
think it's providing...

>
> Does anything in the machine even need -5V or +20V? If not, can I leave the

AFAIK it's only needed if you have core memory. Certainly I've run 11/34
machines without one, with MOS memory and a fair selection of interfaces.
Generally you only need the +5V, +15V, -15V lines.

> bad brick in place? I have: KD11-EA, KY11-LB, DL11-W, MS11-JP, M7850 parity,

I would unplug the 8 pin connector from any brick you're not actually
using, particularly if it seems to be defective. Since that's all the
connections to the brick, the defective brick can be left physically in
the chassis.

> DZ11-A, RK11-D. I'll be adding a RX11 at some point. Someone enlighten me,
> please. :-)
>
> I'm pretty sure I have a spare brick.
>
> Also: what are these signals on the 6-pin backplane mate-n-locks?
> - AC LO
> - DC LO

Power fail lines (like the Power Good line on a PC/AT PSU). Basically,
any device/mounting box can pull those lines low if it detects a power
failure, and the CPU (or other devices can then shut down in an orderly
fashion.

-tony
Received on Tue Mar 04 2003 - 17:56:17 GMT