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Speakers amplifier stopped working

Discussion in 'General Electronics Discussion' started by SiriusFx, Mar 20, 2015.

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  1. SiriusFx

    SiriusFx

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    Mar 20, 2015
    Hello
    I tried to make homemade speakers for my technology class in school. At first everything was running nicely and i listened to it about 2 hours thought whole day. Today i put everything back in place and suddenly it's not working. I attached 2 photos of my "system" and amplifier. I used 12V 1.5A and 12V 0.5A (both worked good) current as power source and 2x 4 ohms speakers if that matters.
    DSCN8328.JPG
    DSCN8329.JPG
     
  2. duke37

    duke37

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    769
    Jan 9, 2011
    The supply is labelled AC/DC so there should not be a problem with the power supply connected the wrong way round. If the rectifier has died, perhaps the TDA 7297 has the wrong polarity and will get hot and the led will not light.
     
  3. SiriusFx

    SiriusFx

    4
    0
    Mar 20, 2015
    So there is no way to get it working again?
     
  4. davenn

    davenn Moderator

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    Sep 5, 2009
    did that board come with a circuit diagram ? if so can you photo / scan it and upload to here

    Dave
     
  5. SiriusFx

    SiriusFx

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    Mar 20, 2015
  6. duke37

    duke37

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    Jan 9, 2011
    Are you using a AC or DC supply?

    The circuit looks quite simple, just a diode to protect the input from wrong polarity, a smoothing capacitor and a resistor to feed the led.

    Check the diode and see where the the voltage stops getting to the led. You could use a 100Ω resistor in the supply if things get hot to limit the current until the fault is found.
     
  7. davenn

    davenn Moderator

    13,798
    1,939
    Sep 5, 2009
    Pretty scary that it says AC or DC input and if AC is used its only a 1/2 rectifier
    the hum would be shocking !!

    don't use anything other than DC 12V and yeah you would need at least 1.5A

    As Duke said, check the diode first and see if it is OK
     
  8. SiriusFx

    SiriusFx

    4
    0
    Mar 20, 2015
    Thank you for your time dealing with newbies. I have this tester http://i00.i.aliimg.com/wsphoto/v1/...-font-b-MAS830L-b-font-Digital-Multimeter.jpg could you tell me what and how should i check if compenents are working (including diode you mentioned).

    And i used a DC adapter when i checked the voltage with tester it said 17,5V even though it says 12V on adapter could it be the reason my amplifier burned? Thank you in advance iam new in electronics and its getting exciting i think i will get some books about it.

    And sorry for bad english.
     
    Last edited: Mar 22, 2015
  9. duke37

    duke37

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    769
    Jan 9, 2011
    To check the diode, switch to the diode position and take a reading both ways round. One way should be open circuit and the other would probably show 0.7V.

    I think the overvoltage has damaged things, possibly blown the led. The amp may be all right, with luck, just make sure that it is not run on too high a voltage. The voltage should be measured across the big capacitor.

    Cheap power supplies are not regulated and are set to a high voltage so that they will still have enough voltage when they are supplying their full rated current.
     
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