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Re: [midatlanticretro] Re: Post-Trenton @ museum

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  • B Degnan
    Thanks Jack helpful info. Fortunately my 8e has never needed any power supply service, but I can compare and contrast them then. bd
    Message 1 of 7 , Mar 7, 2012
      Thanks Jack helpful info. Fortunately my 8e has never needed any
      power supply service, but I can compare and contrast them then.

      At 11:22 AM 3/7/2012, you wrote:

      >--- In midatlanticretro@yahoogroups.com, Evan Koblentz <evan@...> wrote:
      > >
      > >
      > > >> A few of us, led by Degnan, are coming back to the museum
      > after Trenton (this Saturday) to work on the exhibits, etc.
      > > >>
      > > >> Degnan: It's very important that I attend the Trenton evening
      > banquet, so I will give my museum keys to you with some
      > > >> instructions, and I'll arrive in Wall a couple of hours later.
      > > > OK. Anyone who knows about the following types of repairs is
      > welcome to join me
      > > >
      > > > CBM/PET (I will bring what power supplies I have, IIRC MARCH's
      > PET has a bad supply. I will at least determine if the 8V, etc is
      > working, maybe set up a temp supply for testing
      > > >
      > > > PDP 11/20 - power supply testing and checkout. I have been
      > working on H742 power supply systems in prep for this, assuming the 11/20 is
      > > > similar enough.
      > > >
      > > > There's a short in the SWTPc 6800, not sure if this is fixed.
      > > >
      > > > remind me of the priorities. I know we wanted to try to get a
      > mini running, I know most about DEC stuff so I will start there.
      > >
      > > Micros:
      > > - PET 2001
      > > - SWTPc (short in cassette interface, I think)
      > > - Xerox 820 / IBM 5100 -- both have memory trouble
      > >
      > > As for the minis: If the 11/20 can be disconnected from the rack's
      > > overall power supply and plugged into straightforward 110, then great.
      > > If not, then we'll reconsider what to do.
      > >
      > > But, on Herb's page (in the section titled, "How did MARCH acquire the
      > > PDP-11/20?," -- http://www.retrotechnology.com/pdp11/) he wrote:
      > >
      > > "Main chassis without power supply, in rack mounting .... Power supply
      > > for above, H720e .... The power supply (included) has been separated
      > > from the main chassis for convenience in handling."
      > >
      > > I'm not sure if he meant the HUGE power supply mounted to the bottom of
      > > the chassis, or a smaller, separate unit that we stored someplace else
      > > -- if he meant the latter, then the good news is we know which one it
      > > is, because Jeff J. and I just saw it last weekend.
      > >
      >The power supply for the 11/20 is single multi-voltage unit, more
      >like an 8/E than the later multi-supply 11's. You'll find all the
      >info you need on bitsavers. Power to the bus is supplied through
      >multiple paddles that insert into the backplane "above" the unibus,
      >so it's very easy to isolate the supply by removing the paddles.
      >This will still leave the fans (AC feed) hooked up to the main
      >switch so don't worry if the fans come up when you think the p/s is
      >isolated. The supply drops out of the chassis with a few screws and
      >is pretty heavy so it makes sense that it was removed for shipping.
      >It is approximately (from memory) 6x8x24 and sits in the side of the
      >chassis. It is _not_ separately mounted. Vince Slyngstad suggested a
      >nice way to start reforming the caps - grab a handful of 9v
      >transistor batteries and appropriate snap-on connectors and just set
      >up a battery on each cap for a while (I let mine sit for a week).
      >The good caps reform and charge right up; leaky ones drain the
      >battery. No muss, no fuss. Be sure to check for ripple - one of my
      >8/I supplies that seemed to be "about" right (voltage sort of close,
      >but varying up and down a few volts either side of nominal) turned
      >out to be mostly 120 Hz AC through a shorted rectifier leg. There's
      >a lot of 8/I - 8/e in the 11/20 - chassis and hardware are quite
      >similar, switches are the same, even though a different color, etc.
      >Have fun,
      >Yahoo! Groups Links
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