pdp11/45

From: Jacob Ritorto <jritorto_at_nut.net>
Date: Sun Jun 20 19:43:57 1999

On Sun, 20 Jun 1999, Tony Duell wrote:

> It's either a short or something is tripping the crowbar in the H745. Do
> you have the printset for this power supply module? (It's in a lot of CPU
> printsets - the same module was used on the 11/40, 11/45, 11/34, etc).

I have it! In fact think I have all the prints for this machine. I just
don't know how to utilize them beyond setting dip switches. I checked out
the H745 printset and the one covering the PSU-to-backplane connections
and seemed to get the jist of it a bit. What is a crowbar?

> > > You mentioned that 'both -15V outputs are low' Which pins of which
> > > connectors are you measuring? At the PSU there are 3 -15V lines on my
> > > diagrams - pin one of P21 (top PSU rear slot H745), pin one of P25
> > > (bottom PSU, front slot, H745) and pin 4 of P22 (bottom PSU, 12 pin
> > > connector on transformer housing). Which (any/all?) of those are missing?
> >
> > I'm measuring pin 1 on the H745s. I also checked P22, pin4. It gave no
> > reading. Not even -2 volts like the other messed up -15 lines.
>
> Interesting. That could be worth checking first.

Yeah, I checked this again. Totally dead. Just to be sure I'm on the
right wire, are all these connectors on the transformer segments of the
PSUs oriented the same way? If there's any doubt, I'll just have to dig
in there and check the inside of it I guess...

> Silly question : Have you got mains to both PSUs and are all the
> breakers on.

Absolutely. They're both fanning and squealing away. Unfortunately the
red "on" lights seem to be spent. I should certainly replace those, but
haven't checked to see if they're a terribly special item..

> The lower PSU (normally plugged into the left power controller/stip) is
> on all the time. That power controller should be switched to 'local on'.
> The upper PSU is controlled by the panel key, and is plugged into the
> other (right) strip. That power controller is set to remote.

I only have one H860 at the bottom. The lower PSU is plugged into
unswitched and the upper is plugged into switched. I confirmed that the
panel key does engage the H860 and the top PSU, though.

> > 23
> > 24
> > 25
> > 26 |M9200---------| |G747A-|
> > 27 |M9200---------||M7800-------------------------|
>
>
> Bus jumper (to link the 2 Unibuses) and serial (console, I guess) port
>
that's pretty goofy. you'd think they'd have done that on the backplane
itself. It's not like a 920 where it spans 2 system units. oh well...

> It is safe, BTW, to run it with some boards pulled. The obvious things
> that need -15V are the CPU clock, serial port, one of the floating point
> boards (it has a clock on it), and maybe the memory.
>
> If you suspect a short, pull the M7800 and the floating point board set
> (all 4 boards) and see what happens.
>

Tried that, no change. Then I got crazy and kept pulling boards until
there was absolutely nothing left in the machine. I even removed the
power connectors from the core backplanes to be thorough. -15 line is
STILL hanging at -4v. GRRRR.

I deduced that the problem might have been in the backplane or CPU box
wiring, so I tried pulling the power cables off the CPU and rechecking,
but I must have done something different because now all the regulators
are lax (powered up and fanning but not producing). I want to see if the
-15 reg is still doing right when disconnected. It had been at the
outset.

Ugh.

> >
> >
> >
>
> -tony
>
>
>

-jake
Received on Sun Jun 20 1999 - 19:43:57 BST