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Unitron - Apple II clone

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    #16
    Try reseating the LS323 on your disk controller card location C3. The write protect logic is on pin 11.
    Or find another chip to try. Or even another controller card. They show up cheap on ebay. I would think a standard Disk II controller would work,
    just be careful to align the ribbons correctly on the pins

    Larry G

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      #17
      Originally posted by retrogear View Post
      Try reseating the LS323 on your disk controller card location C3. The write protect logic is on pin 11.
      I just noticed that the controller board is labelled 74LS232 at this location, but a 74LS323 is installed. Must be a typo on the board, since the link that snuci gave has a photo of a similar Unitron controller, and both the chip and the label at that location are 74LS323.

      Anyway, I tried reseating the 74LS323 and no luck. However, I checked the signal on pin 11 with a logic probe and there's nothing there. Must be a bad connection somewhere, maybe the cable or something in the drive. I'll do more testing later on.

      Thanks for the help.

      Comment


        #18
        Ok the drive has to be running. I just tested on mine.
        1) Boot up drive 1 with door open so motor is on.
        2) Put probe or meter on the LS323 pin 11.
        3) Just slide a floppy in. It will be 0 then 4V when disk pushes switch then back to 0 when falls in notch cutout

        Comment


          #19
          The cable is definitely the problem (or at least one of the problems): I checked connectivity on each wire between the controller end and the drive end, and wire 20 is broken (no connectivity). Wire 20 carries the write protect signal, which explains why I wasn't seeing a signal on pin 11 of the 74LS323. Now that I looked closely, I can actually see the break in wire 20 right at the controller connector.

          I managed to remove the IDC connector without damaging it, and cut the damaged portion off the cable. However, when I tried attaching the IDC connector again, all the pins were shorted (good thing I checked!). I removed it and tried a second time - same result. I broke the connector taking it off the third time.

          I'm guessing these IDC press connectors can't be re-used? Or is there a trick to installing them?

          Anyway, I'll get a couple more 20-pin IDC connectors and try again later.

          Comment


            #20
            people are reading too much into the brand name of these clone machines.during the peak of cloning in Taiwan, there were thousands of small mom-and-pop shops in Taipei alone assembling these machines under their own brand names from subassemblies sourced from a dozen or so factories. A few larger companies added some interesting twists to their own motherboard layouts, but by and large most are fairly unimaginative clones.

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              #21
              Well, I figured out why the re-attached IDC connector was shorted: the ribbon cable actually has second layer of plastic laminated on covering a copper mesh - some sort of shielding I guess, never seen that before. Anyway, after peeling off a bit of the mesh and plastic, I got the IDC connector on without any more problems, and the drive is now working 100%.

              Comment


                #22
                I've seen that before on genuine Apple Disk ][s, presumably from right around the time original ][s and ][+s came with makeshift shielding.
                Be polite and I may let you live.

                https://www.youtube.com/playlist?lis...5NBVfKX5471R9U

                Comment


                  #23
                  If its not using a mask programmed microcontroller then the eprom will be the same as the other clones of the day, I probably have one here that is the same.
                  Post a photo of your keyboard and I'll upload a suitable eprom image.

                  Originally posted by falter View Post
                  I have pretty much the same machine. Mine was branded a Linden and has different keycaps but the rest is identical. I have been trying to buy another one because the keyboard broke while I was using it to try to restore a real Apple II.. I suspect the eprom is toast. Hopefully one day I can find a dump of it somewhere.

                  Comment


                    #24
                    Originally posted by sid View Post
                    Since I got this machine, I've been keeping an eye on Ebay hoping I could upgrade to a real II+, but damn they are pricey.

                    Hah, I was going to ask you guys if it made sense to swap the eprom with real Apple ones. Are these clones usually 100% compatible, even with Apple brand hardware? I was thinking about getting an Apple Super Serial card for this.

                    (What the best part of owning these machines?)
                    You may want to reprogram the f8/f0 eprom so it displays "APPLE ][" unpatched version of prodos won't boot unless it says apple on the screen. Other than that the ROMS are identical.

                    Comment


                      #25
                      Good thing nothing for the C64 does that. I mean, the first thing one does when burning a custom KERNAL is change the READY. prompt. The second thing is the boot screen.
                      Be polite and I may let you live.

                      https://www.youtube.com/playlist?lis...5NBVfKX5471R9U

                      Comment


                        #26
                        Originally posted by David_M View Post
                        You may want to reprogram the f8/f0 eprom so it displays "APPLE ][" unpatched version of prodos won't boot unless it says apple on the screen. Other than that the ROMS are identical.
                        Ah, good to know. I guess I'll have to pick up a programmer one of these days.

                        Originally posted by KC9UDX View Post
                        Good thing nothing for the C64 does that. I mean, the first thing one does when burning a custom KERNAL is change the READY. prompt. The second thing is the boot screen.
                        Probably never a reason to - were any C64 clones ever made?

                        Comment


                          #27
                          Originally posted by David_M View Post
                          You may want to reprogram the f8/f0 eprom so it displays "APPLE ][" unpatched version of prodos won't boot unless it says apple on the screen. Other than that the ROMS are identical.
                          Or you can patch the ProDOS to ignore the failed ROM checksum and just boot.

                          Comment


                            #28
                            I wonder how ProDOS could do that. Different official ROMs say different things:

                            APPLE ][
                            APPLE ][+
                            Apple //

                            Are just three of the ones I have. I don't recall what the //c says, maybe Apple //c, and my GS doesn't boot anymore; maybe it says Apple ||?

                            Maybe it searches for any of those, or just Apple, in either case? I wonder how early versions would detect later ROMs.
                            Be polite and I may let you live.

                            https://www.youtube.com/playlist?lis...5NBVfKX5471R9U

                            Comment


                              #29
                              I am not aware of any version of ProDOS checking for the string "Apple". Even early versions determine model by looking at some id bytes at $FB1E, $FBB3 and $FBC0. There should be an RTS at $FE1F.

                              Larry G

                              Comment


                                #30
                                Back in the day when Prodos first came out I worked for a company selling apple clones, the only difference was the name string in the F8 ROM. Prodos would not boot past the title screen, simply changing those 8 bytes back to APPLE ][ solved the problem.
                                As far as I know it does a case insensitive check for the word "APPLE". You can easily test it yourself, from memory in an Apple 2+ the name is stored at FB09h with bit 7 set on all characters.

                                Edit: I found this on wikipedia, it confirms my recollection.
                                https://en.wikipedia.org/wiki/Apple_ProDOS

                                Originally posted by retrogear View Post
                                I am not aware of any version of ProDOS checking for the string "Apple". Even early versions determine model by looking at some id bytes at $FB1E, $FBB3 and $FBC0. There should be an RTS at $FE1F.

                                Larry G
                                Last edited by David_M; March 20, 2017, 08:48 AM.

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