Re: [midatlanticretro] Re: Post-Trenton @ museum
- 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 email@example.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.
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