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Looking for a CPU that is GEM specific?

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  • Looking for a CPU that is GEM specific?

    Hello everyone.

    I'm new in this forum.

    I recently "blew up" a CPU from a GEM Plenum Sound board. By mistake of course.
    It's an Intel P8052 AH. (1980)
    But the thing is, it is an OEM version and GEM-10711 is printed on the top.
    I can find replacement CPU's on the Internet but of course they are not the OEM version I'm looking for.

    Does anybody know if and where this kind of chips are still sold ? (Or a whole sound board, or a defective unit...)

    Thank you for any information.

    Rony H

  • #2
    It’s unlikely you’re going to find a replacement online, unless you find a replacement GEM Plenum to use for spares. You’re right a generic Intel P8502 AH won’t work, because you need the specific programming it would have received by GEM prior to being installed at the factory. GEM went bankrupt in 2011, so there is no way to get spares from the company.

    Another user may chime in with a source for a replacement, but failing that depending on what the chip did, you may be able to replace it in the circuit using an Arduino, or convert the organ into a MIDI organ.

    Current: Allen 225 RTC, W. Bell reed organ, Lowrey TGS, Singer upright grand
    Former: Yamaha E3R


    • #3
      Thanks for thinking along with me Larason2.

      My goal is to be able to revert to the situation before my stupid mistake.
      The organ has three sound boards so I'm missing some sounds at this moment. 2 are still working fine.
      I do have all the hardware diagrams of this device and even the internal structure of what GEM called the "Masked 8052 CPU".
      It's in fact a 8032 CPU, a PPI, a latch and 128k ROM.
      But unfortunately no code, no data. And I don't see (at this point) a way to read the data out of the 2 other working chips on the 2 other sound boards. The ROM can't be accessed directly.

      Thanks for any other further comment.


      • #4
        It is hard for me to believe that there wasn't 'collateral damage' when the Intel chip 'blew up'. Probably the best thing would be a replacement board.


        • #5
          If it is indeed and 8032 and not an 8052, you should be able to just replace the chip. The 8032 executes from external ROM. If it's an 8052, the code is in a masked ROM on the chip and there will be no way of replacing it other than the OEM part from GEM.

          Allen 965
          Zuma Group Midi Keyboard Encoder
          Zuma Group DM Midi Stop Controller
          Hauptwerk 4.2


          • #6
            ff Fortissimo
            Leisesturm, since the organ consists of three identical sound boards (with other sample data), I am 100 % sure that it's only the CPU that is defective.
            If I move just the cpu from one board to another, the problem moves along with it which means that I can get both boards to work with a same goodworking CPU.
            This doesn't mean that I don't want to buy a complete sound board if that is what it would take to fix the issue. So, if ever you know where such things are sold, please let me know.

            Admin, yes your last assumption is correct, the rom is embedded in the chip "emulating" a 8052. Since I can't read the rom as it is not accessible from the outside (I have the diagrams) there is in my opinion no other way than finding the OEM part from GEM.
            I'll continue searching.


            • #7
              Hello again everyone. Just sharing some information.

              I have found the chip, a genuine GEM10711.
              In Holland.

              It took some energy to find but it seems that they are still out there somewhere :)

              I'll post whether or not my organ is working again like it should, somewhere next week.



              • #8
                to check if is the processor on the "processor board" is alive when power is on, plug an oscilloscope probe on one of the data or address bus, you will see square waves.
                Also a common failure on this organ is a riboon cable connected to a wrong plug (I've seen that). So do some writing both on the plug & cable before unmouting. I've also done a test program (by replacing the prog EPROM to mine) to check the 8255 PPI (make the IO lines blinking) and it was ok. If the processor seems not to work, check if copper tracks are not dammaged AND test the tracks with a bip-ohmmeter (some cuts are not obviously visible).
                Then check the clock generator (remember it clocks the processor board + 3 slaves boards at about 12 MHz)....

                this is the link to the GEM plenum video that had been fixed :


                • #9
                  As said, here's an update.
                  After having taken a trip to Holland last Friday, I came home with the right chip :)
                  Organ is completely functional again!

                  If ever someone is looking for (older) specific spare parts, I bought this one at "Music Service Center" in "Beegden" NL. It's a repair center with still some stock for (older) musical instruments.

                  Thanks for all contributions.


                  • #10
                    So this is nice!
                    On the first and 3th pic are the process board repaired with "new wires" to fix the cutted tracks. The melted battery has been removed off and is now attached with 2 wires.
                    The 2nd pic shows the rack (without the process board) where you can see the 3 slave boards with a ribbon attached to the "daugther board" with 8032+eprom, it is plug where was the 8052.
                    Attached Files
                    ppp Pianississmo
                    Last edited by f1iwq; 01-17-2022, 09:34 AM.


                    • #11
                      When i converted a friend's Galanti Plenum to a VPO some years ago, I ripped out all the innards. I kept a few boards because they looked "pretty."
                      My friend may still have some others. I can check.

                      I have three smaller boards labelled Plenum each with what looks like an Intel P8032 CPU, a P8255 and an EPROM. Chip dates: '81 and'82.
                      A larger board labelled Slave Board Sounds Generator has four 28627 each accompanied with an EPROM.

                      Could these chips have any value to anybody or should I just chuck the lot?


                      • #12
                        Hello Coenraads, The chips (8032 eprom 8255) are easy to get (I published the file Eprom), but the board may be hard to find, so keep them and let know you have them. 😁


                        • #13
                          Put whatever you wish to sell or give away in the Forum Classifieds. Thanks.

                          Allen 965
                          Zuma Group Midi Keyboard Encoder
                          Zuma Group DM Midi Stop Controller
                          Hauptwerk 4.2