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I need to replace the final and driver transistors for a KLH 765s subwoofer.

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  • lhyounger Nov 11, 2010

    What I was hoping for was a circuit schematic with part numbers or part informatiom.

    Looking at the circuit board there appears to be two large transistors on the heatsink that look to have been burned ( discoloration on the board. I think these are in a push pull configuration. It looks like there are two smaller transistors feeding these finals, but that is a guess. thes two smaller transistors also show some discoloration. Also do you have an easy way to determine if the speaker coil has shorted. Perhaps a nonimal resistance?




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Sorry there is no way to replace the drive transistors yourself. You will need to send in to have serviced.

Posted on Dec 07, 2010

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Well ok..

1.) locate and remove transistor (I guess you know which one is which)

2.) unsolder it,

3.) get replacement (the number of the part is the same one you need avoid substitutes)

4.) re solder it on the board.

Ok By final and driver transistor I'm guessing you meant the 3 pin output IC. Its actually a set of them for each channel has one, Its the largest IC (transistor looking) attached to the heat sinks..

Posted on Nov 11, 2010

  • Rishi Roshan Ali Nov 12, 2010

    actually yes there is a method i use..

    ok this is my personal way, its easy and it works. What I do is work backwards..

    you need a multimeter..

    FOR SPEAKER COIL..
    connect both leads to speaker connectors,, set the multimeter to 20 k resistance
    "gently" push up and down on speaker,, you shoulc see the multimeter move.. If not well speaker coils dead..

    Concerning your board..

    The two large transistors are the ones you need to replace ,, yes there can be other parts damaged as well,, what you do is take your multimeter and tracer the circuit from the burned up transistor all the way back until you find an unburnt part, connect your ground there and set the multimeter to Diode or (beep) now use the positive lead and work your way back touching each component along the circuit to make sure its fine,, If you got a beep its good, if no beep then change him..
    Normally a capacitor goes with the output IC or sometimes only the IC, If you dont see a cap leaking oil or burnt (right around the IC) then just change the IC.. the two small transistors are more than likely switches I dont think there burnt but test them and see..

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