11/73 (ba23) bringup after 12 years in deplorable storage conditions

[Robert Jarratt]

There is no printset that I am aware of the for the H7864 PSU. I have a dead one of these too, I do know which component failed but I don't know *why* it failed. As part of that diagnosis I have made a partial schematic of a couple of parts of the boards.

The schematic for the Primary Control Module is here: http://1drv.ms/1yBzYTN (png) or here: http://1drv.ms/1xFXUnR (Eagle schematic). I may not have drawn it logically, and may have some bits wrong, as it is quite difficult to derive the schematic and it is easy to make mistakes. I don’t know how to identify zener diodes, so all diodes are drawn as ordinary ones. I was also unable to draw the transformers correctly as I don't know their spec and pinout.

Regards

Rob

> -----Original Message-----
> From: cctech [mailto:cctech-bounces at classiccmp.org] On Behalf Of Jacob
> Ritorto
> Sent: 21 November 2014 05:46
> To: General Discussion: On-Topic Posts
> Subject: Re: 11/73 (ba23) bringup after 12 years in deplorable storage
> conditions
> 
>   Well, things inside were clean and pretty minimally configured, so, with all
> apologies, I jumped the gun and applied power, but I'm afraid the old girl just
> didn't survive the twelve years of temperature transients.
> 
>   The illuminated ba23 power rocker switch lights up, but that's absolutely it.
> No fans, no familiar power supply squeal, no drive spinup, nothing on the
> seven-segment CPU state display on the rear.  Seems thoroughly dead.
> 
>   I guess I need to start tearing it down and debugging the power supply as I
> recall that it was at least doing more than this before the years of bad storage.
> 
>   So I need to find power supply diagrams and start tracing things out, right?
> Any ideas as to where to begin?
> 
> 
> On Thu, Nov 20, 2014 at 4:34 PM, Jacob Ritorto <jacob.ritorto at gmail.com>
> wrote:
> 
> > Good deal.  I guess I'm just gonna go for it after a cursory
> > inspection and dusting.  It has stayed utterly dry; just the temp and
> > dust were concerns.  I'll report back in a while..  Thanks!
> >
> > On Thu, Nov 20, 2014 at 3:55 PM, Ian S. King <isking at uw.edu> wrote:
> >
> >> At the very least, take a good long look at the power supply and its caps.
> >>
> >> Has the storage, as bad as it's been, been dry?  If not, you'll
> >> almost certainly have corrosion all over the place, especially in the
> >> fastons ISTR run power to the backplane.  (I haven't looked at my own
> >> 11/73 in a few years, but it's in a dry, temperature-stable
> >> basement.)
> >>
> >> Best of luck! - Ian
> >> On Nov 20, 2014 12:32 PM, "Jacob Ritorto" <jacob.ritorto at gmail.com>
> >> wrote:
> >>
> >> > Hey all,
> >> >   I've been getting the bug worse and worse to start working on a
> >> > real pdp11.  The Raspberry Pi / simh emulation is fantastic, but my
> >> > hunger
> >> for
> >> > authenticity is becoming rampant.  I haven't run the youngest in my
> >> fleet
> >> > of pdp11s, the 11/73, since circa 2002 and if I recall correctly,
> >> > it was becoming flaky and popping out to ODT inexplicably from time
> >> > to time
> >> back
> >> > then (I think this is the one with the notoriously combustible
> >> > power
> >> supply
> >> > wires that probably haven't been ECO'd yet -- need to get to that too).
> >> > It's been lying in a warehouse in western Pennsylvania with no heat
> >> > and
> >> a
> >> > lot of dust.  So, worst case, we're talking temperature transients
> >> around
> >> > 110 F and -20 F with no protection.  It did stay quite dry.
> >> >
> >> >   Think it'd be bad to simply blow the dust off and fire it up?
> >> >
> >> > thx
> >> > jake
> >> >
> >>
> >
> >