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33941RE: [midatlanticretro] LA120 Destination^Wfaults unknown

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  • Brian Schenkenberger, VAXman-
    Jan 14, 2014
    • 0 Attachment
      Cory Smelosky <b4@...> writes:

      >On Tue, 14 Jan 2014, Brian Schenkenberger, VAXman- wrote:
      >
      >> Cory Smelosky <b4@...> writes:
      >>
      >>> Afternoon,
      >>>
      >>> I have the PSU operational again.
      >>>
      >>> 2 +12, 1 -12, and -5V are all present.
      >>>
      >>> These voltages could be wrong: (pin-wise) on J2.
      >>> Pin 6: 4.97VDC
      >>> Pin 5: GND
      >>> Pin 4: GND
      >>> Pin 3: -12.28VDC
      >>> Pin 2: about 12VDC
      >>> Pin 1: about 12VDC
      >>>
      >>> +/-24VDC are both present on J4 where they should be.
      >>> The motors do not run and there is no voltage present at fuse F2 (the fuse
      >>> OTHER than the line feed one. There is +24VDC present at the line feed
      >>> one.) There is continuity between the -24V pin and the non-line-feed
      >>> motor fuse. No fuses blow.
      >>>
      >>> With J2 disconnected, power draw drops from ~65W to ~42W. Several random
      >>> resistors checked (in-circuit) that should measure 540Ohms measure about
      >>> 588Ohms. No LEDs light up and there is no bell. No components are
      >>> particularly warm to the touch with power removed.
      >>>
      >>> Anything with this taste wrong to you? I'm completely stumped. The motor
      >>> ran before I started working on the PSU. When I was doing repair work on
      >>> the PSU (caused by my own mistakes -- oops) I had it disconnected from
      >>> the LA120 entirely save for a couple tests with test resistors. There was
      >>> no -12V present when these tests were performed and +5 would've measure
      >>> +4.77VDC.
      >>
      >> Are you aware of and or have copied of these?
      >>
      >> http://vt100.net/docs/la120-tm/la120tm1.pdf
      >> http://bitsavers.informatik.uni-stuttgart.de/pdf/dec/terminal/la120/MP00663_LA120_Oct79.pdf
      >>
      >
      >Yup. I have been browsing through them.
      >
      >> I have a fully functional LA120 if you need me to check voltages for you.
      >> However, I believe you have the appropriate voltages within tolerances.
      >>
      >
      >Yes please. Do check them in relation to which pin is which.
      >
      >> Are both fuses (carriage return and line feed) good? Are you sure that
      >> the ribbon cable from the logic board is connected to the keyboard logic
      >> board? Make sure pin 1 and pin 1 on each are correct. The cable has a
      >> marker to coincide with pin 1 on the main board. Check that whatever
      >> color coincides with pin 1 there is closest on the connection on the
      >> keyboard logic to the keys themselves. Do you have the carriage return
      >> motors sense wires connector properly oriented on the main logic board?
      >> The paper out (pins 1 & 4) and cover open (2 & 3) (note I may have them
      >> backward but it doesn't matter) won't matter if you connect ti upside
      >> down/backward.
      >
      >I'll need to look more closely at those pins. I could have any number of
      >them orinted wrong. Both fuses pass a basic continuity test.

      +-----+-----+-----+-----+
      (1) | +24 | 0 | -24 | N/C | J4
      +-----+-----+-----+-----+
      | +24 | 0 | -24 | N/C |
      +-----+-----+-----+-----+
      | +24 | 0 | -24 | N/C |
      +-----+-----+-----+-----+


      +-----+-----+
      (1) | 0 | 0 | J2
      +-----+-----+
      | +12 | 0 |
      +-----+-----+
      | -12 | +5 |
      +-----+-----+


      These voltages were measured with the power supply connected to the printer
      logic board. The printer was on but not actively outputting any characters.
      The +5 measured +5.2 which is within 5%. All other voltages were spot on!
      Measurements from common ground with meter's lead connected to the wire of
      C48's negative lead.
      --
      VAXman- A Bored Certified VMS Kernel Mode Hacker VAXman(at)TMESIS(dot)ORG

      Well I speak to machines with the voice of humanity.
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