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SWTPC 6800 Troubleshooting

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  • antiquekid4
    Hi folks, So I have had this SWTPC 6800 for about three years now. It worked great when I got it. I went to turn it on the other week and although the power
    Message 1 of 14 , Feb 15, 2012
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      Hi folks,

      So I have had this SWTPC 6800 for about three years now. It worked great when I got it. I went to turn it on the other week and although the power supply came right up, the prompt "$" via RS-232 did not. The computer had just been sitting in a low-dust climate-controlled environment for maybe six months. I reseated all of the ICs to no avail. Nothing changed from best I can tell while it was sitting, so I'm very confused as to why it all of a sudden stopped working. That typically doesn't happen.

      I'd love to get this computer running again. I see activity on the CPU with my 'scope, but I'm not seeing much of anything on the data lines on the bus. I'm going to try and check the individual ICs on the bus, but are there any other obvious things to check? All the 5V regulators check out, and the power supply is again quite healthy. The checkout guide from SWTPC (on Michael Holley's page, which seems down right now) was not very helpful.

      Thanks!

      Kyle
      W4GNU
    • Evan Koblentz
      ... Your email name looks familiar; are you on other vintage computing boards? Either way, please introduce yourself -- how you found us, where you live,
      Message 2 of 14 , Feb 16, 2012
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        >> So I have had this SWTPC 6800 for about three years now.

        Your email name looks familiar; are you on other vintage computing boards?

        Either way, please introduce yourself -- how you found us, where you live, collecting interests, etc.
      • jaevans@pcisys.net
        ... wh en I got it. ... Kyle, I am afraid that machine is a lost cause - you should ship it to me so I can put it out of its misery ;) 73 - john - n0hj ...
        Message 3 of 14 , Feb 16, 2012
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          > Hi folks,
          >
          > So I have had this SWTPC 6800 for about three years now. It worked great
          wh> en I got it. ...

          Kyle,

          I am afraid that machine is a lost cause - you should ship it to me so I
          can put it out of its misery ;)

          73 - john - n0hj


          ---------------------------------------------
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        • Bob Applegate
          ... But you re in 0-land... I m probably closer up here in 2-land, so it ll be cheaper for him to send it to me ;-) 73 Bob - K2UT
          Message 4 of 14 , Feb 16, 2012
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            > 73 - john - n0hj

            But you're in 0-land... I'm probably closer up here in 2-land, so it'll be
            cheaper for him to send it to me ;-)

            73
            Bob - K2UT
          • jaevans@pcisys.net
            ... I m sorry, I should ve mentioned that I would send him a sympathy payment that would more than cover shipping. ;) john ... This message was sent using
            Message 5 of 14 , Feb 16, 2012
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              > > 73 - john - n0hj
              >
              > But you're in 0-land... I'm probably closer up here in 2-land, so it'll be
              > cheaper for him to send it to me ;-)
              >
              > 73
              > Bob - K2UT

              I'm sorry, I should've mentioned that I would send him a sympathy payment
              that would more than cover shipping. ;)

              john

              ---------------------------------------------
              This message was sent using Endymion MailMan.
              http://www.endymion.com/products/mailman/
            • Evan Koblentz
              ... 73 - john - n0hj Lots of new members lately! John, please introduce yourself. Thanks.
              Message 6 of 14 , Feb 16, 2012
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                >> you should ship it to me so I can put it out of its misery ;)
                73 - john - n0hj

                Lots of new members lately! John, please introduce yourself. Thanks.
              • B Degnan
                ... I may have missed some messages, but where are you located? Can you be more specific about what no longer works? Did you have terminal I/O? Is it a disk
                Message 7 of 14 , Feb 16, 2012
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                  At 09:02 AM 2/16/2012, you wrote:
                  > >> you should ship it to me so I can put it out of its misery ;)
                  >73 - john - n0hj
                  >
                  >Lots of new members lately! John, please introduce yourself. Thanks.

                  I may have missed some messages, but where are you located? Can you
                  be more specific about what no longer works? Did you have terminal
                  I/O? Is it a disk system?

                  Bill
                • Bill Sudbrink
                  ... Having just restored a 6800 myself, I would recommend pulling everything except the CPU and the serial card. The RAM onboard the CPU card (unless it is
                  Message 8 of 14 , Feb 16, 2012
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                    antiquekid4 wrote:
                    > I'd love to get this computer running again. I see activity on the CPU
                    > with my 'scope, but I'm not seeing much of anything on the data lines
                    > on the bus. I'm going to try and check the individual ICs on the bus,
                    > but are there any other obvious things to check? All the 5V regulators
                    > check out, and the power supply is again quite healthy. The checkout
                    > guide from SWTPC (on Michael Holley's page, which seems down right now)
                    > was not very helpful.

                    Having just restored a 6800 myself, I would recommend pulling everything
                    except the CPU and the serial card. The RAM onboard the CPU card (unless
                    it is intentionally disabled) should be enough (and in the right place)
                    for SWTBUG or MKBUG to come up (giving you the $ prompt). If you don't
                    get anything there, I would suspect the UART on the serial card or the
                    "baud" clocks on the SS-30 bus. Possibly, the address decode logic on the
                    motherboard could be bad. My first suspect would simply be the pin
                    connections
                    to the cards, but since you say you reseated all of the ICs, I assume you
                    reseated all of the cards in that process. My 6800 is running SWTBUG, if
                    you want to compare scope traces and/or other behavior with a working
                    system,
                    let me know.

                    Bill Sudbrink
                  • J. Chris Hausler
                    Hi Kyle, This should be obvious but remove all boards from the system except the processor card and whatever serial interface card you are using (MP-S, MP-C,
                    Message 9 of 14 , Feb 16, 2012
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                      Hi Kyle,

                      This should be obvious but remove all boards from the system except the processor card and whatever serial interface card you are using (MP-S, MP-C, third party). I've had issues with marginal bus drivers on memory boards loading down the bus in the past. If you have more than one serial card available, swap those as I've seen the RS-232 driver go bad. One of my B2 motherboards is bad and I haven't been able to find the problem and although I haven't worked on it in quite a while I know it's the motherboard as I have another which works fine with the same daughter boards plugged in.

                      73, Chris Hausler


                      -----Original Message-----
                      >From: antiquekid4 <antiquekid3@...>
                      >Sent: Feb 16, 2012 2:43 AM
                      >To: midatlanticretro@yahoogroups.com
                      >Subject: [midatlanticretro] SWTPC 6800 Troubleshooting
                      >
                      >Hi folks,
                      >
                      >So I have had this SWTPC 6800 for about three years now. It worked great when I got it. I went to turn it on the other week and although the power supply came right up, the prompt "$" via RS-232 did not. The computer had just been sitting in a low-dust climate-controlled environment for maybe six months. I reseated all of the ICs to no avail. Nothing changed from best I can tell while it was sitting, so I'm very confused as to why it all of a sudden stopped working. That typically doesn't happen.
                      >
                      >I'd love to get this computer running again. I see activity on the CPU with my 'scope, but I'm not seeing much of anything on the data lines on the bus. I'm going to try and check the individual ICs on the bus, but are there any other obvious things to check? All the 5V regulators check out, and the power supply is again quite healthy. The checkout guide from SWTPC (on Michael Holley's page, which seems down right now) was not very helpful.
                      >
                      >Thanks!
                      >
                      >Kyle
                      >W4GNU
                      >
                      >
                      >
                      >------------------------------------
                      >
                      >Yahoo! Groups Links
                      >
                      >
                      >
                    • Bill Sudbrink
                      ... Ha! Great minds think alike!
                      Message 10 of 14 , Feb 16, 2012
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                        J. Chris Hausler wrote:
                        > This should be obvious but remove all boards from the system except the
                        > processor card and whatever serial interface card you are using (MP-S,
                        > MP-C, third party). I've had issues with marginal bus drivers on
                        > memory boards loading down the bus in the past. If you have more than
                        > one serial card available, swap those as I've seen the RS-232 driver go
                        > bad. One of my B2 motherboards is bad and I haven't been able to find
                        > the problem and although I haven't worked on it in quite a while I know
                        > it's the motherboard as I have another which works fine with the same
                        > daughter boards plugged in.

                        Ha! Great minds think alike!
                      • Kyle Owen
                        Well, let me introduce myself then. I was active on the VCF for a while, a couple of years back. I moved on to other hobbies, but a class in assembly
                        Message 11 of 14 , Feb 16, 2012
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                          Well, let me introduce myself then. I was active on the VCF for a while, a couple of years back. I moved on to other hobbies, but a class in assembly programming for the HC12 microcontroller got my interest in the 6800 rekindled.

                          Other projects include a 1976 Fiat 124 Spider (read: money bucket), restoring and collecting fountain pens, and restoring/collecting antique radios and other tube electronics.

                          I have a couple of IBMs, including an XT and AT, as well as a Tandy CoCo and 200, a C64, a Compaq Deskpro/386, and I'm working on getting a CompuPro or two.

                          Yes, I am trying to start the computer with only the CPU and MP-S boards installed. I have four 8k RAM boards, an MP-C, the EPROM programmer, and a couple of other boards, but all were taken out for this.

                          I also have the tape interface and the CT-64, but the latter doesn't work. Project for another day, for sure. I picked up a Zenith Data Systems terminal, a slightly later unit with external keyboard, so that should work well if I'm trying to be slightly more authentic.

                          I am running SWTBUG, so I might take you up on the offer of 'scope shots, Bill. I'm first going to see about testing the motherboard by itself, but it that's not it, maybe you can send some bus line waveforms my way.

                          Thanks for all the tips, everyone. I'll see what I work out with the bus, but since exchanging the MP-S for the C didn't work, I think I can boil it down to the motherboard or CPU card.

                          Glad to see some fellow hams on here. Can't say I'm too surprised, though! :)

                          73!

                          Kyle
                          W4GNU
                        • Evan Koblentz
                          ... Keep in mind that VCF in these parts = Vintage Computer Festival, which has been around a lot longer than the unaffiliated VC Forum.
                          Message 12 of 14 , Feb 16, 2012
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                            >> I was active on the VCF for a while

                            Keep in mind that VCF in these parts = Vintage Computer Festival, which has been around a lot longer than the unaffiliated VC Forum.
                          • B Degnan
                            I have a couple of SWTPc s; The one I exhibited last year at VCF E with the teletype, and the other has a hacked MP-S serial card set to mystery purpose and
                            Message 13 of 14 , Feb 16, 2012
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                              I have a couple of SWTPc's; The one I exhibited last year at VCF E
                              with the teletype, and the other has a hacked MP-S serial card set to
                              "mystery purpose" and many IC's removed, so I plan to return to
                              standard 9600b. The 2nd unit's processor and RAM are fine. 8K. I
                              don't know about the motherboard. It's a work in progress, probably
                              for after the upcoming VCF.

                              Bill
                            • Christian Liendo
                              Hey AntiqueKid ya made it. I m the guy that talked to you on Reddit. To my fellow MARCHians... There is a vintagecomputing subgroup on Reddit and I have been
                              Message 14 of 14 , Feb 17, 2012
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                                Hey AntiqueKid ya made it.


                                I'm the guy that talked to you on Reddit.

                                To my fellow MARCHians...


                                There is a vintagecomputing subgroup on Reddit and I have been somewhat active on it:

                                http://www.reddit.com/r/vintagecomputing

                                I met AntiqueKid and he told me about the 6800 and I told him to come here, he would be a good fit. 

                                I also posted about VCFE and an article on why you want to go to VCFE

                                So welcome, maybe with luck you can pass around NJ and meet with us.
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