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31000Re: [midatlanticretro] Acquired a PDP-8/E

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  • David Gesswein
    May 27, 2013
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      On Mon, May 27, 2013 at 12:47:21AM -0500, Kyle Owen wrote:
      > On Tue, May 21, 2013 at 11:09 AM, David Gesswein <djg@...> wrote:
      >
      > Measuring the voltages again, I see the 5V bus is 5.12V, 15V is 15.24V,
      > -15V is -15.12V, and V2 is 4.32V. V2 sounds pretty low...what should I
      > check for this bus?
      >
      V2 is power good. It isn't a voltage bus. The manual says 3.75-5 is good.
      Its just driving gate inputs to shut down core access when the power falls.
      8/E, 8/M processor maintenance manual volume 1 table 4-7.

      > Also, what's the fix for the melting fuse holder problem? I see that
      > there's a 10A fuse in the fuse holder, but the rating next to the holder
      > says 25A. I'd expect a 25A fuse to have a lower resistance, yes? Would that
      > help then?
      >
      Here's DEC's official information.
      http://www.pdp8online.com/bklatt/262.png

      Sounds like its the holder and not the fuse. Since your load is low if you
      have inspected it and didn't see any problems you should be ok. I have
      two heavily loaded backplanes and did have that faulure. I put another
      holder in and added an additional 5V power supply for the second backplane
      so I wouldn't be stressing my power supply.

      > I also noticed that my 8/E has only one Unibus. Did they not by default
      > come with two? Maybe that's why there's a 10A fuse?
      >
      It was an ordering option. I know of several systems with only one backplane.

      The wire contacts rating may be the limiting factor so with you only having
      one set connected that may be why your fuse is lower value.
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