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33943RE: [midatlanticretro] LA120 Destination^Wfaults unknown

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

      >On Tue, 14 Jan 2014, Brian Schenkenberger, VAXman- wrote:
      >
      >> 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.
      >>
      >
      >My J4:
      >
      >> +-----+-----+-----+-----+
      > (1) | +24 | 0 | -24 | UNK | J4 (all the below ones NC are same)
      > +-----+-----+-----+-----+
      > | NC | 0 | NC | UNK |
      > +-----+-----+-----+-----+
      > | NC | 0 | NC | UNK |
      > +-----+-----+-----+-----+
      >>
      >>
      >> +-----+-----+
      > (1) | +12 | 0 | J2
      > +-----+-----+
      > | +12 | 0 |
      > +-----+-----+
      > | -12 | +5 |
      > +-----+-----+
      >>
      >
      >Looking at this, I see a +12 in mine that is not in yours. I can make
      >that go away, however.

      I'd reconcile things with the schematics before you go making changes that
      might cause you problems. Also, I believe that there are fusable links or
      resistors on the power supply board. Have you checked that they're intact?

      --
      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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