How do i check speaker ohm from this digital multimeter

Discussion in 'General Electronics Chat' started by kevinkhan, Dec 3, 2010.

  1. kevinkhan

    Thread Starter New Member

    Dec 3, 2010
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    Im new to electronics and dont have a clue how to use a multimeter

    this is the one i have
    http://www.sinometer.com/jpg/MS8230B.jpg

    One of my speakers is not working properly. only a slight sound is coming from it. I dont think its the speaker driver or sub woofer.

    I had the same problem with another speaker before and when i brought it to the repair shop they said "there was a dry circuit and one of the circuits needed to be re soldered. I think this is they same problem with my current speaker.

    Any ideas where i could look on the circuit board to see if i can trouble shoot the fault.

    Here is the circuit board diagram

    http://www.jblproservice.com/pdf/MRX...ies/MRX515.pdf

    Thanks
     
  2. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    you can check the operation of the speaker with a nine volt battery( not on very very small speakers). touching it with one polarity should make the cone extend and reversing that should make the cone draw in.

    There should be no scratchy sound or rubbing detected when you gently push the cone down by hand.

    A dc Ohm meter set to the low ohm scale should read about 6 ohms for most speakers( very close to the stated impedance of the speaker).

    If the speaker coil has been overheated, you will feel or hear the scratchy sound when you move the cone, and if not you may also detect a subtle difference in cone response with the nine volt battery, when you compare it to a known good speaker.
     
  3. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    Couldn't you just switch wires from one channel to the other and see if the problem moves with the swap? If the problem moves to the other speaker it's the amp/driver, if the same speaker is still not working it's the speaker thats at fault. No meter needed!
     
  4. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    The speakers are probably ok unless they are scratching/crackling.

    The bad solder joint they were speaking of was most likely in the crossover unit, the one with the inductors and capacitors on it.

    Switching outputs between woofer and tweeter won't hurt the woofer, but may destroy the tweeter, as they aren't built to withstand low frequencies at any useful power level.
     
  5. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    thatoneguy - I based my reply on this in the first post - ''One of my speakers is not working properly. only a slight sound is coming from it. I dont think its the speaker driver or sub woofer.''
     
  6. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    The inductors should measure very low resistance, the capacitors should read open circuit. It would be hard to test the caps in circuit due to the inductors and other caps in parallel and series. Check continuity across the board inductors, look for any loose solder joints, etc. Make sure both speakers measure continuity from the wires to the crossover.

    Good photos of the board top and bottom may help us to give pointers.
     
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