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Class D "trouble" shooting

Discussion in 'Troubleshooting and Repair' started by Dustysnakes, Apr 5, 2013.

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  1. Dustysnakes

    Dustysnakes

    4
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    Apr 5, 2013
    Hi guys,
    First timer on this forum and I hope you can help me out. I have a powered PA subwoofer in my shop here. Class D 2 channel one powers the line array tops above it. TVI BT1200 is the amp model. Powers on and even amplifies and passes audio. I am not that familier with this amp type so im not really sure whats going on here. I have done physical check as well as some DMM component checks in the usual areas and did find a leaky cap in the power supply section. The noise that comes along with the audio however is not 60hz I put an RTA in front and actually got a fundemental of around 800hz. Could that be switching frequency passing through the output filter or should it be much higher. Any help you offer would be much appreciated.
    thanks
    Dusty
     
  2. Dustysnakes

    Dustysnakes

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    Apr 5, 2013
    did I say something wrong guys? I see 44 views and no replies. Also another thought and I hope it isn't the case, This thing has a very multiple coiled transformer and it was mentioned that it got a power surge. Any chance of noise being sent across those coils?
     
  3. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,271
    Nov 28, 2011
    Five hours is not long. Keep waiting; I think you will get more replies.

    What does "the line array tops above it" mean?

    You didn't describe the problem. You mentioned an extra noise... audible in the speaker?

    Have you looked at the waveform? It might be interesting to know what shape it is.

    The "multiple coiled transformer", is that in the power supply?

    Most importantly, do you have a link to a schematic?

    It could also be helpful to see a few photos, just to give us all some idea what we're dealing with. It's obvious enough to you, but we can't see it!

    I'm not saying I will be able to help - I have no experience with Class D. But you're likely to get more responses if you provide more information.
     
  4. Dustysnakes

    Dustysnakes

    4
    0
    Apr 5, 2013
    Sorry let me clarify a bit. This is a high end pa amplifier. It is mounted in a subwoofer enclosure but powers both the sub and 4 high frequency and mid frequency drivers that are externally connected. Unfortunately I have not been able to find a schematic or service manual for it (waiting on reply from tvi). I also due to the size have not taken it in my shop to scope it. I did check the output with the hz setting of my multi and got 60. I'm not sure if either my ears have become to bad to determain frequency or if I'm getting a faulty reading. Yes that output would be to the speaker and it does it on both sides of the amp which makes me immediately point to power supply. The transformer in this case appears to be at a few places although the ps being the main one. I was getting plus and minus 5, 15, and 160 v dc when I checked the regulators but there seems to also be some sort of inductor in it for the final stage of the amplifier.
     
  5. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,271
    Nov 28, 2011
    If you think the noise is 800 Hz it won't be the switching frequency of the power supply! Switching supplies run at 20 kHz and higher. You really need to find out more about the noise - the frequency and waveshape could be helpful to know, and check the power supply rails to see if it's coming in on them.

    Is there any circuitry that's common to both channels? I guess there's a single preamp then the signal is split using an active crossover for biamping?

    Does the noise vary with the volume control setting, if there is one? What about the tone controls?

    A schematic, or at least a few photos to start with, could be helpful.
     
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