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Get a board Xerox 820-II working fine

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  • enrlaz
    Hello everyone, I got a board Xerox 820-II without any other components and without disk controller. After changing the video sync and created a composite
    Message 1 of 4 , Mar 23, 2013
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      Hello everyone,
      I got a board Xerox 820-II without any other components and without disk controller.
      After changing the video sync and created a composite video on video i have the correct prompt.
      I made a keyboard interface to convert a PS2 keyboard in parallel with the same schematic that works well with my Ferguson Bigboard I and the other card Xerox 820-I.
      I saw that on the xerox 820-II board there are almost 2 ICs with the name Signetics 3341PC (U102 and U101) that are between the U65 (system and Keyboard PIO) and the 72LS74 (U96 and U97) that come to connect to the keyboard input (see sheet 7 of thsi schematic http://bitsavers.trailing-edge.com/pdf/xerox/820-II/Xerox820-II_Schematics.pdf).

      I come to requests:
      1) The keyboard does not write. I read on a post that I can not find anymore that without the inclusion of the disk controller card into its slot the keyboard would not write.
      Perhaps because there is not anymore the continuity of the chain interrupt (see at the bottom of sheet 8 close to U65 into this schematic http://bitsavers.trailing-edge.com/pdf/xerox/820-II/Xerox820-II_Schematics.pdf )?
      2) If i not find the disk controller card I was thinking about to self-build it on a bareboard hoping that the diagram at the bottom of the last pages at http://bitsavers.trailing-edge.com/pdf/xerox/820/Xerox820_ServiceMan.pdf is accurate. Where can I find a card edge connector male 72-pin 2.54mm pitch?
      3) You also have some suggestions for me?
      Thanks so much
      Enrico – Pisa – (Italy)
    • enrlaz
      Hello everyone, I got a board Xerox 820-II without any other components and without disk controller. After changing the video sync and created a composite
      Message 2 of 4 , Mar 24, 2013
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        Hello everyone,
        I got a board Xerox 820-II without any other components and without disk controller.
        After changing the video sync and created a composite video on video i have the correct prompt.
        I made a keyboard interface to convert a PS2 keyboard in parallel with the same schematic that works well with my Ferguson Bigboard I and the other card Xerox 820-I.
        I saw that on the xerox 820-II board there are almost 2 ICs with the name Signetics 3341PC (U102 and U101) that are between the U65 (system and Keyboard PIO) and the 72LS74 (U96 and U97) that come to connect to the keyboard input (see sheet 7 of thsi schematic http://bitsavers.trailing-edge.com/pdf/xerox/820-II/Xerox820-II_Schematics.pdf).

        I come to requests:
        1) The keyboard does not write. I read on a post that I can not find anymore that without the inclusion of the disk controller card into its slot the keyboard would not write.
        Perhaps because there is not anymore the continuity of the chain interrupt (see at the bottom of sheet 8 close to U65 into this schematic http://bitsavers.trailing-edge.com/pdf/xerox/820-II/Xerox820-II_Schematics.pdf )?
        2) If i not find the disk controller card I was thinking about to self-build it on a bareboard hoping that the diagram at the bottom of the last pages at http://bitsavers.trailing-edge.com/pdf/xerox/820/Xerox820_ServiceMan.pdf is accurate. Where can I find a card edge connector male 72-pin 2.54mm pitch?
        3) You also have some suggestions for me?
        Thanks so much
        Enrico – Pisa – (Italy)

        PS: This board not have 2 ICs just on the central http://cgi.ebay.it/ws/eBayISAPI.dll?VISuperSize&item=290885192545

        This one has 2 ICs U101 and U102 in the same postions http://www.ebay.com/itm/Xerox-820-II-Motherboard-Z80A-CPU-/150617117645?ViewItem=&item=150617117645&lgeo=1&vectorid=229466&nma=true&si=7VCHVvqGfhDvXOhHABsDRVUKnNY%253D&orig_cvip=true&rt=nc&_trksid=p2047675.l2557 no info on ist schematic about this differenze of ist release
      • Jeff Jonas
        ... Wow, just like me in the 80s. Perhaps it s the same kit ? Did it include the 3 EPROMS? I started gathering the parts but gave up because - just the cost
        Message 3 of 4 , Apr 7, 2013
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          --- In midatlanticretro@yahoogroups.com, enrlaz <no_reply@...> wrote:
          > I got a board Xerox 820-II without any other components and without disk controller.

          Wow, just like me in the 80s.
          Perhaps it's the same "kit"?
          Did it include the 3 EPROMS?

          I started gathering the parts but gave up because
          - just the cost of the sockets would've been prohibitive
          - the entire unit in cabinet with keyboard, CRT
          went surplus so cheap that even I valued my time enough
          to get one and just give up.

          I'm unsure where the bare board & instructions went
          because it changed hands a few times by now.

          > After changing the video sync
          > and created a composite video on video i have the correct prompt.

          YAY! Good going!

          > I made a keyboard interface
          > to convert a PS2 keyboard in parallel

          Which one? PIC based?
          I'd love to see the schematic & firmware.

          -- jeff jonas
        • enrlaz
          Some answers first: Wow, just like me in the 80s. Perhaps it s the same kit ? Did it include the 3 EPROMS? A: I not know: I bought this one:
          Message 4 of 4 , Apr 11, 2013
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            Some answers first:
            Wow, just like me in the 80s.
            Perhaps it's the same "kit"?
            Did it include the 3 EPROMS?
            A: I not know: I bought this one: http://www.ebay.it/itm/Vintage-Xerox-820-II-Motherboard-/330719705046

            I started gathering the parts but gave up because
            - just the cost of the sockets would've been prohibitive
            - the entire unit in cabinet with keyboard, CRT
            went surplus so cheap that even I valued my time enough
            to get one and just give up.
            A: I'd love to buy a complete system, but in Italy that appears rarely on internet and it cost SOOOOOO much AND buying in USA and adding its shipping it would cost SOOOOOO MUCH

            Well below what it happens from the last my post:

            I sent the post at least 10 days ago, but I saw that it was only released today.
            Since then there have been other more events with VCF.

            1) how to convert ps2 to parallel interface: look here http://www.vintage-computer.com/vcforum/showthread.php?32129-Ferguson-Big-Board-1-monitor-rom&highlight=kyeakel i attached the schematic and the pic 16f84 code. here it assembled for my xerox 820-I board i put in a classic PC case http://www.flickr.com/photos/67772736@N07/7419081302/in/set-72157630233712582/

            2) xerox 820-II Floppy disk controller card: as i told i bought an ALONE xerox 820-II motherboard. i discovered that i need a FDC card. It's not easy to find. It's schematic is at the end of the xerox 820-II service manual here: http://classiccmp.org/dunfield/miscpm/x820serv.pdf (it is not much readabe). Then i find some pics on Internet of this FDC card: http://www.vintage-computer.com/vcforum/attachment.php?attachmentid=12294&d=1363516923 AND , I discovered the presence of an IC named 733w01522 (U1) on the photo of the original PCB i can't idenfiy and also i cannot read on the schematic not very readable
            reported at the end of xerox820-II service manual.

            Thanks for contribution of Chuck Guzis from the VCF he told me that the 733w01522 is a PROM and it is equivalent at 74S288 but also to others IC as reported here http://www.hobbyroms.com/proms.html.

            U1 (74S288) and U2 (74S174) together constitute a "finite state machine" (so they told to me cause I'm not so expert) whose purpose is to provide a read clock and a read data to the chip WD1797 from raw data received from the drive.

            Then I need to discover the code to insert into that chip (without having the original chip programmed with me!).

            Upon the recommendation of Chuck Guzis I found the code listing on page 12 of the manual of the FDC1797's application notes http://bitsavers.informatik.uni-stuttgart.de/pdf/westernDigital/FD179X_Application_Notes_Jun80.pdf . At this point, trusting to this code I'd need to buy a programmed 74S288 (or equivalent).

            After all this I was finally trying to figure out if it sould be better to use of a schematic published on an old issue of Microcornucopia: https://www.dropbox.com/s/4f8kblogrlzdr9m/FDC_from_Micro_Cornucopia_%2322_Feb85.pdf Who so far wrote that article decided to build himself a FDC controller card for his xerox 820-II extracting a block of its schematic from a Kaypro-II's
            schematic really making very few changes and using a FDC WD1793 + WD9216 for external separator data.

            Due to its small number of components, and having already a spare kaypro II working board with WD1793 and its WD9216 all seems a bit more simple buying a connector like this http://www.futureelectronics.com/en/technologies/interconnect/connectors-pcb/header-plug-board-mount/Pages/9795113-EBM36MMNN.aspx , a perfboard an mounting components lie shown in the pic on the microcornucopia's article. Of course i'll look for the FDC on Internet, but a people told me: If you know what this thing is, you probably need it and i added: if you NOT know what it is you'll throw it away easly.

            Regards
            Enrico - Pisa (ITALY)
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