11/73 (ba23) bringup after 12 years in deplorable storage conditions
jacob.ritorto at gmail.com
Sat Nov 22 16:33:06 CST 2014
Thanks for the replies. Hope to remember enough about electronics and
get enough guidance to be able to use the diagrams you've made, Rob.
Okay, I opened the power supply and checked for corrosion (none at all),
worked back and forth all of the push-on connectors thoroughly and replaced
the PSU into the chassis. I don't yet understand where to insert the
resistors, but I guess anywhere there's 12v and 5v would be sensible.
So now, with no boards at all in the chassis, I do at least get a few
lights on the little front panel but unfortunately not the "DC OK" light
and still no fans. To get them to stay on, I have to kind of 'trick' the
PSU by turning it off, waiting a second, then turning it back on.
While I'm not stickler for perfect authenticity, I do respect it to a
degree. So I'm wondering but am hesitant to ask: Would it be more sensible
to just buy a commodity PC power supply that has lots of 5v and some 12v,
find a way to bolt it in and rework the wiring to fit? Or do you think
it's likely I'll be able to bring this power supply back to safe, reliable
condition without getting in over my head?
Suggestions on where to begin tracing the thing would be most welcome,
please and thanks!
It's been some decades since I've dealt with electronics at this level of
detail and in the interim, someone has made off with my nice fluke meter,
so I don't even have anything to check volts with at the moment. Going to
find another now. Got lots to re-learn here; thanks for bearing with..
On Fri, Nov 21, 2014 at 2:33 AM, Robert Jarratt <robert.jarratt at ntlworld.com
> 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.
> > -----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
> > So I need to find power supply diagrams and start tracing things out,
> > 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
> > >>
> > >> 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
> > >> > 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
> > >> >
> > >>
> > >
> > >
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