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DX7II-D white noise problem

@mickeyratt All Messages By This Member #21014 Dear Friends I would like to ask for your help. I have recently purchased a faulty DX7II-D model, which is producing the problem you can hear in the YouTube video below.? The battery is 2.9V, I upgraded the ROM to v.:1.9 firmware, I don't have a cartridge for it, so I loaded the INTERNAL memory contents via MIDI, but unfortunately no change. What is worrying is that the noise also comes in test mode (as shown in the video) instead of the 880 Hz test tone. The power supply voltages are fine. Do you think this is the kind of error that could be produced by a PCM54 DAC failure? I'm afraid not. It is reacting to the pitch bender, this seems more like a structural fault, which unfortunately could probably be a fault in the EGM or OPS chips. What is your opinion? Thanks in advance! Greetings from Hungary!
Florian Anwander All Messages By This Member #21015 开云体育 Hello I cannot tell what is the cause of this behaviour, but it looks like there is an extremely high feedback on the operator 2 (I think it is operator 2, which allows feedback - I don't own a Mk2). At least your example with the tubular bells in the beginning of the video shows, that the sound becomes tonal in the release phase. I'd check to which value the feedback is set. Florian Am 26.05.24 um 16:37 schrieb csabi@...: toggle quoted message Show quoted text Dear Friends I would like to ask for your help. I have recently purchased a faulty DX7II-D model, which is producing the problem you can hear in the YouTube video below.? The battery is 2.9V, I upgraded the ROM to v.:1.9 firmware, I don't have a cartridge for it, so I loaded the INTERNAL memory contents via MIDI, but unfortunately no change. What is worrying is that the noise also comes in test mode (as shown in the video) instead of the 880 Hz test tone. The power supply voltages are fine. Do you think this is the kind of error that could be produced by a PCM54 DAC failure? I'm afraid not. It is reacting to the pitch bender, this seems more like a structural fault, which unfortunately could probably be a fault in the EGM or OPS chips. What is your opinion? Thanks in advance! Greetings from Hungary!
[email protected] All Messages By This Member #21016 You might find this thread I started a while back interesting: /g/YamahaDX/topic/tx802_troubleshooting/96731773 In that case it was a broken EGM IC. Yours sounds different but it could be the same problem. Op zo 26 mei 2024 om 16:37 schreef csabi via <csabi=[email protected]>: toggle quoted message Show quoted text Dear Friends I would like to ask for your help. I have recently purchased a faulty DX7II-D model, which is producing the problem you can hear in the YouTube video below.? The battery is 2.9V, I upgraded the ROM to v.:1.9 firmware, I don't have a cartridge for it, so I loaded the INTERNAL memory contents via MIDI, but unfortunately no change. What is worrying is that the noise also comes in test mode (as shown in the video) instead of the 880 Hz test tone. The power supply voltages are fine. Do you think this is the kind of error that could be produced by a PCM54 DAC failure? I'm afraid not. It is reacting to the pitch bender, this seems more like a structural fault, which unfortunately could probably be a fault in the EGM or OPS chips. What is your opinion? Thanks in advance! Greetings from Hungary!
@mickeyratt All Messages By This Member #21018 Thank you Florian for your reply. The error occurs even in test mode, when only the 880Hz sine wave sound should be on the output, which makes me think that it is definitely a hardware problem, not a software parameter problem. Thank you!
@mickeyratt All Messages By This Member #21019 Thanks for your suggestion, I read it, I also think there is a hardware problem. I have a good DX7S motherboard that uses the same chipset, I'll start comparing the signals around the two big chips with an oscilloscope to see if I can learn something. Thanks!
[email protected] All Messages By This Member #21020 The oscilloscope was fun but it did not teach me much in the end. It was mainly by carefully listening and editing patches that I convinced myself that the OPS2 was working and that the EGM had to be the problem. Use the init patch instead of presets, it is easier to reason about. Try varying the algorithm. Try low values for R1 (attack). Can you get clean sounds? (I.e. no noise.) Op ma 27 mei 2024 om 17:00 schreef csabi via Groups.Io <csabi=[email protected]>: toggle quoted message Show quoted text Thanks for your suggestion, I read it, I also think there is a hardware problem. I have a good DX7S motherboard that uses the same chipset, I'll start comparing the signals around the two big chips with an oscilloscope to see if I can learn something. Thanks!
@mickeyratt All Messages By This Member #21021 Thanks for the tip! To tell you the truth, I've never programmed an FM synthesizer before, so I'd need a serious learning curve :) With the oscilloscope, I thought that at least I could find out if the DAC is faulty. I looked at the signals on the good DX7S motherboard during the test tone generation (880Hz- same test program here) and even without a logic analyser you can see pretty well what is happening around the DAC (DA2-16 legs and SH1/2), you can definitely spot if there is a problem here. Of course, the communication between EGM - OPS and CPU is a whole other problem unfortunately.

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