Digitech GNX3 Guitar Effect

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  • mike123333
    Senior Member
    • Oct 2011
    • 196
    • USA
    #1

    Digitech GNX3 Guitar Effect

    Hello everyone, I am trying to repair a friends Digitech GNX3 Guitar Effect, that started with taking a long time to boot up. I found several bad caps that I replaced and still the problem was there. As I was probing voltages I accidentally slipped and either hit the 12 volt input from the voltage regulator to 3.3V output or hit the 3.3V output to ground. either case the LED light lit up and then when I powered down then back up, there was nothing the unit was completely dead. at that point in time I thought maybe that the microcontroller (U5) has been corrupted. The MNFR suggested downloading the software program and trying to update the firmware. The also supplied me with the schematics of the unit. I went thru the voltages and found nothing bad. I was unable to communicate with the micro controller the program would just time out.

    I purchased a scope for testing, as I was probing the midi in and out I noticed that the midi in was not sending any data bits, so I replaced the opto coupler 6N138 which gave me the data bits being sent tot he unit Micro controller. But nothing coming back from the unit Midi out. Probing with the scope showed nothing no data being sent out TX line. The midi usb cable I have is fully functional as I have tested it on my musical keyboards so it does send and receive.

    Thinking it may be a bad micro controller I replaced it with an Atmel which is comparable to the the Winbond micro controller ( I also replaced the caps for the crystal from 15 pF to 5pF), they note that using a higher crystal frequency one needs to replace the one capacitor with a 4-5M ohms resistors which I have not done yet I am not sure whether this would do anything as I probed the crystal and it is running at 24 Mhz. After replacing I do have several LEDs come on but nothing else, still no output from the controller TX and the software still times out and no signs of data bits from the micro controller using the scope. I am at a lost here and can't seem to get much help from Digitech.

    If anyone can help out here that would be great. Maybe a way of programming the microcontroller, which I am not sure whether the firmware resides in the chip or external to it. I have attached TDS and SM.
    Attached Files
    Last edited by mike123333; 02-10-2017, 09:08 PM.
    Tags: None
    • mike123333
      Senior Member
      • Oct 2011
      • 196
      • USA
      #2
      Re: Digitech GNX3 Guitar Effect

      Does anyone know whether the Atmel micro controller can be programmed in circuit after being installed or does it need to be programmed ahead of installation?

        Comment

        • CapLeaker
          Leaking Member
          • Dec 2014
          • 7991
          • Canada
          #3
          Re: Digitech GNX3 Guitar Effect

          depends on if there is a programming port available, like serial interface, jtag etc. I've flashed them either or before. The Atmel comes empty so one would have to flash it, otherwise it wont do anything at all. Usually with something like a first initialize.bin and then the what ever program.bin. Of course you can do that with a out of circuit programmer too.

            Comment

            • mike123333
              Senior Member
              • Oct 2011
              • 196
              • USA
              #4
              Re: Digitech GNX3 Guitar Effect

              Originally posted by CapLeaker
              depends on if there is a programming port available, like serial interface, jtag etc. I've flashed them either or before. The Atmel comes empty so one would have to flash it, otherwise it wont do anything at all. Usually with something like a first initialize.bin and then the what ever program.bin. Of course you can do that with a out of circuit programmer too.
              Thanks for the response, I did do more research and found that there is an ISP software for reading and flashing. I am in the process of building a parallel interface to communicate with the microcontroler. I have an older computer with XP in hwhich the software will talk with otherwise current OS are out of the question. I am not familiar with understanding bin folder and programming so my knowledge is very limited. here is the firmware zip file in text that needs to be flashed to the microcontroller. do You think this will cover everything that it needs to work? I also included the interface schematics.
              Attached Files

                Comment

                • mike123333
                  Senior Member
                  • Oct 2011
                  • 196
                  • USA
                  #5
                  Re: Digitech GNX3 Guitar Effect

                  Is there a standard initialize bin available or is that something unique for each device?

                    Comment

                    • CapLeaker
                      Leaking Member
                      • Dec 2014
                      • 7991
                      • Canada
                      #6
                      Re: Digitech GNX3 Guitar Effect

                      I am not sure if the firmware will take or not without the initialize.bin. For the Atmel's I use I have a initialize.bin and a firmware.bin and they are used in controllers. Try flashing the Atmel with the firmware only a couple of times back to back. Sometimes the flash will not take correctly the first time and it has to be done again.

                        Comment

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