car amplifier repair

Discussion in 'Technical Repair' started by Jason87, Jun 27, 2012.

  1. Jason87

    Thread Starter Member

    Dec 10, 2009
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    Basically my friend had just had his amplifier repaired (he is a bit careless)

    He was placing the amplifier in the car, and basically he was giving power to the amplifier while the car was on...

    I don't know what he exactly did but he is saying that he by mistake touched or overchanged the plus or negative terminals.

    The amplifier fell in protect mode and is stuck there.

    So basically i have a situation where no RCA or speaker cables are attached and the amplifier is still in protect mode.

    The amplifier is a 2channel amplifier branded Boschmann.

    Now i opened up the unit and figured out the various power supply transistors and output transistors with the other various components.

    If i understood well in such situation it is most like that the output transistors are shorted.

    Thus i tested with the multimeter set as diode check.

    The output transistors type is BD912 and complementary BD911.

    The ohmage between the legs of the transistors 1-3, 1-2, 2-3 are all in the megaohm range while regarding the voltages achieved in diode check,

    between legs 1-2 and 1-3 it is 0.481v while between legs 2-3 it is 0.745v

    These are the values that read for the output transistors, can anyone describe me what they mean?


    I also gave a look to the power supply transistors type IRFZ24N

    between legs 1-2 it is in the kohm range, between legs 1-3 it is 320ohm, while between legs 2-3 it shows 0ohm.

    Can anyone give me a help what shall i do to repair it?
     
  2. praondevou

    AAC Fanatic!

    Jul 9, 2011
    2,936
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    Can you post the model # of the amp? Maybe we can find a schematic.
     
  3. Jason87

    Thread Starter Member

    Dec 10, 2009
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    on the board i have written AP-2300TB, the model of the amp is PCH-2600SX

    Thanks
     
  4. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,986
    745
    The IRFZ24N is a power mosfet N-type with an internal diode across the drain and source (pins 2-3) so should read 0.7 volts on diode test one way and open circuit other way

    if its short circuit it may be blown, you need to unsolder it and test it.

    as for the bd911/ bd912 these are a "matched pair" of transistors one is PNP the other is NPN, (these must be changed together,) so you need to reverse your meter leads to get the same results on the PNP as you do on the NPN.
     
  5. Jason87

    Thread Starter Member

    Dec 10, 2009
    39
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    i got one of the power mosfets of from the board, it is giving me 0.539volt between pins 2 and 3 and giving me OL when i reverse the probes. Is that ok? Should i take one of the bd912 transistors off the board to test them correctly?
     
  6. Jason87

    Thread Starter Member

    Dec 10, 2009
    39
    0
    i took the BD912 off, i am getting OL between pins 2 and 3 now, while on the board i read a voltage output of 0.745v
     
  7. Jason87

    Thread Starter Member

    Dec 10, 2009
    39
    0
    any help????
     
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