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Pioneer SX434 receiver amp

Discussion in 'Vintage Analog Gear' started by PhantomBox, Oct 1, 2009.

  1. PhantomBox

    PhantomBox Active Member

    This might not be the most indicated place, but I'll give it a shot anyway:

    I have a Pioneer SX434 receiver amp (schematics at http://fileshare.eshop.bg/downloadsm/36776/Pioneer_SX-434.html). This is a great sounding amp so I'd like to keep it.
    Here's the thing:
    Right channel sounds ok but left channel doesn't. On the AWK-034 (power amp section) I replaced Q16 (2SC1318), Q20 (2SD131) and Q22 (2SB507) - all transistors went short - as well as R73 (18ohm 1/2W) - burnt out. I also checked R83 / R85 and R79 / R81 and they are fine.
    But I still got no output. Instead it makes a harsh hum sound.

    Am I missing something?

  2. Kev

    Kev Well-Known Member

    compare things to the working channel

    check the power supply rails

    work your way through the signal path
    find the spot where things change

    that pdf file you pointed to is a PCB layout and not a schematic
    makes things a little hard to visualise the topology
  3. PhantomBox

    PhantomBox Active Member

    Now that you mention it, I had a hard time with the pcb layout, also. With a REAL schematic it would be a lot easier to separate both channels. You don't happen to know where I could get the "schematic" schematic?
  4. djmukilteo

    djmukilteo Well-Known Member

    Did you check each of the capacitors in that channel? Caps are the first thing to go!
  5. Kev

    Kev Well-Known Member

    power supply rails
    and electro caps

    get an ESR meter

    I can't find a schematic ... I see you posted at diyaudio.com also with no luck
  6. djmukilteo

    djmukilteo Well-Known Member

    If you buy higher quality caps to replace....it will sound better too....

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