No signal into DJ mixer - Need help locating PCB with problem

Discussion in 'General Electronics Chat' started by mynamesalex, Jul 8, 2013.

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  1. mynamesalex

    Thread Starter Member

    Oct 4, 2012
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    Hey guys,

    I have a strange problem here. I just bought a damaged DJM 800 mixer with intentions of fixing it yet it seems to be a little more difficult to fix than I initially thought. I was wondering if you guys could help me out a little bit. The overall problem is that the board is getting no audio input signal anywhere. It powers up and functions just fine other than that. All faders and knobs work as well. I tested in all four channels and I'm getting no levels on any of them. I also tested a microphone and got no levels through that either. I have a feeling one of the cards isn't receiving signal and passing it to the board. I just have to figure out where that problem is.

    I was hoping someone would be able to help me trace the signal as I don't really know how to do that. I'm eager to learn all of this so I think this is a good project for me. If someone could point me on the right track as to how I should go about finding the problem that would be awesome. Also, I have the exploded views and other information on all the electronic aspects of the board I'm just not exactly sure how to read and utilize the information. I'll try to attach that to this post. I also have the service manual for the unit but it is too large to attach. I can send that to someone if needed. Thanks a lot guys.

    - alex
     
  2. wayneh

    Expert

    Sep 9, 2010
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    Pretty tough without a schematic. But what exactly do you mean about what you have observed? It sounds like there is no output at all and no indication of life except power, even with hot inputs? When the knobs and faders "work", you mean they move smoothly, not that they perform their expected function?
     
  3. MrChips

    Moderator

    Oct 2, 2009
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    Possibly doable but you will need a few items:

    1) camera so that you can post photos
    2) circuit schematic
    3) multimeter
    4) audio source such as mp3 player, microphone
     
  4. mynamesalex

    Thread Starter Member

    Oct 4, 2012
    53
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    There is a "test mode" on the mixer when powered on a certain way. It tells you which knobs are functioning and such when you move them and all turned out fine. That's how I know there's no general physical problems with the knobs and such. I'm very good with use of audio gear so I'm positive that this is an internal issue and not just me being silly and wiring incorrectly. I have tested the RCA inputs for each channel with a RCA to stereo plug going into an ipod and macbook and neither have produced a signal on any channel. Is the schematic I posted not detailed enough? I'm going to upload the service manual which has EVERYTHING on it. Thanks for the prompt responses, guys! Do you need me to take pictures of the inside of the mixer or will the schematics do? They're very detailed. Also, Can someone instruct me on how to correctly use the multimeter to test the current going in and out of the separate cards in the mixer once there is a better understanding? Thanks again.

    EDIT: Here's the link for the service manual with detailed schematics of everything. http://www1.zippyshare.com/v/89488021/file.html
     
    Last edited: Jul 8, 2013
  5. wayneh

    Expert

    Sep 9, 2010
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    Well, with the documentation your odds are going up.

    Have you run thru the diagnostics instructions?

    How about re-loading firmware?
     
  6. mynamesalex

    Thread Starter Member

    Oct 4, 2012
    53
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    Yeah I ran through the diagnosis steps but all that told me was that the knobs and faders were all functioning properly. Sadly consumers don't really have the equipment to re load firmware on this mixer. That really shouldn't be the problem though. I need to figure out where to test with a multimeter. So anxious to start using this!
     
  7. MrChips

    Moderator

    Oct 2, 2009
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    The good news is you have a complete Service Manual with schematics.
    The bad news is this is digitally controlled. Don't get your hopes too high as yet.

    Since you say the controls seem to work but you can't get any audio from any channel, then we want to look for a fault common to all channels.

    We begin with the power supply.

    Look on page 71 you will find a connector CN201. I have not had the time to look over the schematics completely. (My computer connected to the printer is on the blink so I can't get a good look at the schematics.)

    Your job is to locate all the power supply voltages both on the schematics and on physical connectors or test points. Then you will use the multimeter on a voltage scale and verify that all the voltages are present.

    Make notes. Write down the location of the test point, the test signal name and the measured voltage. At a glance I can see:

    +3.3V
    +5V
    +8V
    +12V
    +15V
    -15V
    -12V (maybe?)

    Of interest, there is a MUTE circuit and a MUTE voltage and a MUTE signal. Keep this in mind.

    Confirm the supply voltages first before jumping head on into the MUTE circuit.
     
  8. Relayer

    New Member

    Jan 1, 2013
    18
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    mynamesalex, does the unit have a master mute button or individual mute buttons for each channel?
    Regards,
    Relayer :D:D:D
     
  9. MrChips

    Moderator

    Oct 2, 2009
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    He said he was experienced with audio gear so one would assume that he had already looked into the MUTE control. But then again, never assume anything. We all make mistakes.
     
  10. MrChips

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    Oct 2, 2009
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    Reading your first post I assume that you are not getting any lights lit on the Channel Level Indicators when you have proper audio signal and even with the TRIM and FADER controls set to maximum.

    This would suggest that the MUTE signal is not the cause of the problem.
     
  11. mynamesalex

    Thread Starter Member

    Oct 4, 2012
    53
    1
    Thanks for taking the time to help me with this. I really appreciate it. Any chance you could break that down for me a tad more? I've never gone too in depth with circuitry as of yet. I'm a computer engineering major at school but I'm just starting so I haven't quite got into the crazy stuff I'm looking forward to yet. How would I locate the PS voltages on the schematics? Would I be calculating these or are they listed? I actually think all the voltages are listed towards the end of the manual. Also, where would I use the multimeter on the power supply to test? I know it sounds like I'm a complete idiot right now with all of this but don't lose hope in me yet! I just need a bit of a start as I'm still new to all of this. I learn fast though! Thanks again guys. As per the mute function, I'm not sure what that can be. There's no "mute" buttons on the mixer itself. The only mute function I could think of would be the "talk over" function that the microphone has. When the switch is set to talk over, the music will be muted and the microphone will activate until the switch is changed.
     
  12. mynamesalex

    Thread Starter Member

    Oct 4, 2012
    53
    1
    Yep. No signal with trim and fader at max either. Though once while I was testing at max volume there was sudden loud distortion/static for about a second and then it cut out.
     
  13. Relayer

    New Member

    Jan 1, 2013
    18
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    The reason I ask is that it cold be a muting circuitry problem and nothing to do with the mute button, as that could be a common factor.
    Regards,
    Relayer :D:D:D
     
  14. mynamesalex

    Thread Starter Member

    Oct 4, 2012
    53
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    That is a good point. Any way I could check this mute circuit?
     
  15. MrChips

    Moderator

    Oct 2, 2009
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    I think the mute circuitry only affects the audio output.
    If you are not getting any lights that could be a DSP problem.
    I would check for power on the analog chips first.

    Any more tips from me will have to wait until I can look over the schematics.
     
  16. mynamesalex

    Thread Starter Member

    Oct 4, 2012
    53
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    I'm going to attempt to check those voltages in the morning. Could ya give a tad bit more info on how I should go about finding and testing the voltages? I'm not entirely sure where to place the hot lead from the multimeter on the PSU board. Thanks!
     
  17. Relayer

    New Member

    Jan 1, 2013
    18
    1
    As MrChips has stated, check your voltage rails first. Its the easiest to do. :)

    The negative probe (Black) should go to a good ground point. Basically any metal part excluding heatsinks. You can always place it on the metal part of a pot.
    With your "Hot" Probe (Red), it should go to the voltage rails in turn. You're going to have to check the schematic on where to place the probe for each voltage rail.
    Regards,
    Relayer :D:D:D
     
  18. mynamesalex

    Thread Starter Member

    Oct 4, 2012
    53
    1
    So I think I'm starting to understand all of this as I just found the connector I'm supposed to test. It has twelve holes (rails?) just as the schematic said. Quick question. The holes seem to be a little too small to stick the probes in. Would it be bad to disconnect the cable from the PSU board and just test the metal prongs on the board where the cable was connected?
     
  19. MrChips

    Moderator

    Oct 2, 2009
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    Do not disconnect the cable to test voltages.
    You want to be able to measure the voltages when all loads are connected.
    You will have to compare the circuit schematic with the component layout in order to find suitable test points.

    I just don't have the time right now to look at this for you. Someone else might help out or do the best you can. Don't just go poking around with a probe carelessly. You don't want to short out something and make matters worse. The last time someone was doing this that is exactly what happened.
     
  20. mynamesalex

    Thread Starter Member

    Oct 4, 2012
    53
    1
    Gotcha. I have to follow the pinout on the schematic and find a point where each pin lands to test for voltage there, correct? Yeah I had a feeling it wouldn't be such a good thing to just poke around. Good thing I asked first. Thanks for the continuous help though. Let me know whenever you have some time.
     
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