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My old Philips AH848 amplifiers won't give sound anymore, i've removed the left channel power transistor and one of it is blown, what else should i check now?

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  • jetbot007 Sep 08, 2010

    Btw they are power transistors (darlington) with a big heat sink. 2 for left channel and 2 for right channel.
    I haven't checked it by re-joining the fuse again, should i start the amplifier and check if right channel gives any output?

  • jetbot007 Sep 08, 2010

    Got it, i'll go keep one pair which isn't blown, and reconnect the fuse.

  • jetbot007 Sep 08, 2010

    Okay, i'll check those transistors later, i have to go and i have a serious headache now.
    I'll reply, when i'll get back later.

  • jetbot007 Sep 09, 2010

    Okay, so I followed those small transistors, there are 4 of them. Each one for each darlington. Collector of two BDV64C and two BDV65C are connected to each other with a small capacitor. So it's yet not sure which pair is of left and which is of right. And the transistors are not insulated to heat sink. And yea those big resistors were connected to emitter.

  • jetbot007 Sep 09, 2010

    And all the four transistors Collector and Emmiter are short.

  • jetbot007 Sep 10, 2010

    Okay, rechecked the diode and transistor.
    Right heatsink's collecter are short to chasis.
    Left's collecter shows current around 70
    The emitter and base for all darlington transistors show approximately same current output.

  • jetbot007 Sep 10, 2010

    Okay, rechecked the diode and transistor. Right heatsink's collecter are short to chasis. Left's collecter shows current around 70 The emitter and base for all darlington transistors show approximately same current output.

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You may have a blown channel. Check for fuses inside but I don't think that it will help. Repair if the channel is dead is not worth doing as the amps value is probably lower than repair cost.

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Sounds like your Power FET's are gone. Take it to a shop that specializes in high end or vintage gear. ....good luck...Rob

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Look for low valued resistors that may look ok, but be open. Check the emitter resistors (.22 or .47 ohms). Check the transistors in the driver circuit as well.
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