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Data General Nova 2/10

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    Data General Nova 2/10

    Recently I have been debugging and fixing a Nova 2/10 I found in a barn.

    It has the following boards:
    • CPU
    • 16 K core
    • 8 K core
    • Cassette I/O
    Here is a short log of what I have done so far.
    • Cleaned out several decades worth of accumulated dust, spider webs, dead insects and other debris.
    • Fixed the +15V rail in the power supply.
    • Fixed the leaking filter capacitor issue which kept tripping the RCD.
    • Replaced the broken AC3 examine/deposit switch.
    • Replaced two of the broken console (front-panel) lights. I could only find 2 of the miniature lights locally but have more on order from both the US and China.
    • Debugged an apparent problem on the console board and proved to myself that it is not the culprit. The problem is with the AC0-AC3 deposit switches where switch settings don’t take (i.e. a deposit behaves like an examine).
    • After studying the CPU board schematics I gained a reasonable understanding of the processing for the ACx deposit machinery and finally traced the problem to a faulty "Console ROM 0" which does not assert the /1WEN when needed. I am not sure what the exact failure mode of this bipolar PROM is. It may be that the fuse "healed" or that the associated open-collector driver transistor has died.
    A tiny 2 word program incrementing AC0 runs successfully.

    Best regards
    Tom Hunter

    #2
    I have since replaced the faulty "Console ROM 0" so ACx deposits work perfectly.

    The TTY subsystem on the "Cassette I/O" board works perfectly after replacing a faulty N8H90 hex inverter shown as U113 in the schematics which is U109 on the actual PCB. I found it by tracing the SET_TTI_DONE signal from pin 19 of U40 (the LSI UART) following the tracks to locate the hex inverter. I replaced the faulty part with a socketed SN74F04 which is pin and speed compatible with the Signetics N8H90.

    I have added the "Program Load" option to the CPU board so that the "Program Load" switch loads and runs a bootstrap program (found in the schematics from Bitsavers).

    The 8 K core has a dead short between the +15V (VINHR) and GND and also between +5v and GND. There are a bunch of electrolytic and tantalom caps which might be causing this. To find the shorting compoent I am thinking of precision Ohm-meter or maybe applying current limited +15 V and then watch it with a thermal camera. Of course I have neither of these gadgets, but maybe there is a much simpler method I have not thought of.

    Any thoughts on how to find the short(s) short of unsoldering components starting with capacitors?

    Thanks
    Tom

    Comment


      #3
      Very cool
      Computers: Amiga 1200, DEC VAXStation 4000/60, DEC MicroPDP-11/73
      Synthesizers: Roland JX-10/SH-09/MT-32/D-50, Yamaha DX7-II/V50/TX7/TG33/FB-01, Korg MS-20 Mini/ARP Odyssey/DW-8000/X5DR, Ensoniq SQ-80, E-mu Proteus/2, Moog Satellite, Oberheim SEM
      "'Legacy code' often differs from its suggested alternative by actually working and scaling." - Bjarne Stroustrup

      Comment


        #4
        I forgot to mention in my earlier message that I have replaced all the front panel lights with "#2176 Miniature Bulb Wire Terminal Base" I bought from "Bulb Town". The originals were failing and also the old wire terminals have become very fragile. Some broke just looking at it.

        In the past two days I have replaced a faulty address bus driver (SN75453) so that /MAB3 is now fully functional and there is no longer the nasty wrap-around of addresses 010000 (octal) and above.

        I replaced a faulty Signetic N8H90 with a functionally identical SN7404 hex inverted where one of the inverters was bad causing the TTY Input done flag to not be set when a character was received from the TTY.

        I also replaced a faulty SN7474 which impmented the busy/done flags for TTY Output.

        Finally now all the diagnostics I have access to (and know how to run) work and pleasingly even BASIC runs perfectly.

        The last job will be the nasty dead short on the 8 K core board and maybe a cleanup of the "Cassette I/O" board badly butchered by a previous owner.

        Best regards
        Tom
        Last edited by thunter0512; November 16, 2021, 06:35 AM.

        Comment


          #5
          Here is a photo of the Nova 2/10 successfully running the mother of all DG Nova diagnostics: the Nova Multiprogramming Reliability Test (MORT).

          IMG_20211117_202859860.jpg

          Comment


            #6
            MORT, as a name for a diagnostic program, is perfect !
            Current fleet
            TRS80 Model 4 - BBC B - Tatung Einstein - PCW9512 - PET 3032 - C64 - ZX81 - Spectrum 48K - Amiga A500 - Apple II europlus - Apple iMAC G3. Sharp MZ-80K. - IBM 5160 XT - Multibus 286/10 - Micro PDP 11/73 - Rainbow PC100A - MicroVax II - MicroVAX 3100, 3300, VAX 4000 VLC & 4000 Model 96 - AlphaStation 225 Apricot PC - Apple Performa 6200 - Apple Mac IIcx - Osborne 1 - ACT Sirius 1

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              #7
              Where did you get your copy of Basic from? been looking for that for years for my systems.

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