How to diagnose B&W speaker 'protect mode'

Discussion in 'Technical Repair' started by Elliott Balsley, Aug 31, 2016.

  1. Elliott Balsley

    Thread Starter New Member

    Aug 31, 2016
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    Someone gave me a Bowers & Wilkins A7 wireless speaker, and I'm trying to figure out how to diagnose and fix it. It works great for about 20 minutes, then starts flashing red, which means it's in "protect mode" and needs to be sent into the manufacturer for repair. Unplugging the power for a few seconds is enough to reset it, then it works again. I'm guessing maybe something is overheating? Visually inspecting the capacitors inside, I don't see anything wrong. What's the next step to find the problem?
     
  2. #12

    Expert

    Nov 30, 2010
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    Get the schematic and start measuring voltages.
     
  3. Elliott Balsley

    Thread Starter New Member

    Aug 31, 2016
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    I already asked the company for a schematic; it's not available. They want $180 for a repair.
     
  4. #12

    Expert

    Nov 30, 2010
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    Are you good enough to make your own schematic by tracing out the board?
    Without any sort of schematic there is nothing but guessing.
    We don't have any idea what the speaker is measuring to conclude that it should protect itself.
     
  5. RichardO

    Well-Known Member

    May 4, 2013
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    You can try cooling different sections of the circuit to see if it will reset without cycling power. I suspect that it will not.

    If that is the case then you will have to do it the hard way. Cool a section. Cycle power and see if it takes longer to fail. Repeat.

    A spray circuit cooler will work but you will use a lot of it. An alternative is to judiciously apply isopropyl alcohol using a small brush. Use alcohol with as little water as possible to keep from shorting out sensitive circuits.
     
  6. #12

    Expert

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    Cooling is better than nothing, but we don't know if it has an MPU or just some basic power measurements.
    Being a wireless speaker..does that mean is has its own power supply? Is it batteries or a wall plug?
     
  7. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    Does it have a fan? How long does it work after you unplug it for just a few seconds?
     
  8. RichardO

    Well-Known Member

    May 4, 2013
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    Lacking a schematic I think it is time for some good pictures to help answer these (and future) questions.
     
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  9. #12

    Expert

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    Right. Enough guessing.
    ps, the real world calls. I have to go do some chores now.
     
  10. KeepItSimpleStupid

    Well-Known Member

    Mar 4, 2014
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    "protect" for a typical amplifier means there is DC on the speaker terminals, but it can mean anything. The DC voltage should be no more than +-0.750 and usually very near zero.

    If this is a class AB amplifier, then the current across the emitter resistor is increasing over time and eventually reaches the "protect" threshold.

    Protect could mean many other things.
     
  11. Elliott Balsley

    Thread Starter New Member

    Aug 31, 2016
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    These are the two main boards, front and back. There is another board for the WiFi.
    This unit has AC power input. No batteries, no fan. It has WiFi and RJ-45 for AirPlay, and a combo input jack for 3.5mm analog and Mini Toslink.

    It enters protect mode even when there's no audio playing. These are high-res photos if you download them.

    IMG_2625.jpg IMG_2626.jpg IMG_2627.jpg IMG_2628.jpg
     
  12. #12

    Expert

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    No chance I can do that.
     
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  13. absf

    Senior Member

    Dec 29, 2010
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    You mean without a schematic?
    Looks like class-D Amp to me..

    Allen
     
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