SX-828 low filter

Discussion in 'Pioneer Audio' started by Matt Mincer, Dec 6, 2018.

  1. Matt Mincer

    Matt Mincer AK Subscriber Subscriber

    Hay All,

    I have an SX on the bench. Everything works great except the low filter toggle switch makes a horrendous pop when switched in either direction. It's so loud that it shuts the speaker protect relay off for a few seconds. Any thought on what could be causing this?



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  2. markthefixer

    markthefixer On Hiatus, dealing with Dad's estate full time Subscriber

    Looking in the BOM of the service manual, it lists CSSA type caps. These are the sky blue sanyo solid aluminum electrolytic caps. Sanyo tried to make solid aluminum "tantalum" type caps. The caps get electrically leaky over time.
    We derisively call them "cap-sistors", as they eventually fail shorted.

    C31 and C32 by the low filter switch are probably failing, although C37 and C38 probably haven't failed yet, and prevent the DC from affecting the biasing of Q7 or Q8.

    You saw "the ten worst transistors" thread, the sky blue Sanyo CSSA caps deserve to be in a "bad caps" thread.

    They are a guaranteed failure eventually.

    They are routinely preemptively replaced along with 2sc1451, 2sa725, 2sa726, 2sc1312, 2sc1313,
    Last edited: Dec 7, 2018
    Matt Mincer likes this.
  3. EastPoint

    EastPoint Factory Code No. 4200 Subscriber

    Milwaukee, WI
    It’s the blue caps on the preamp board. Almost all 828s do it. While you’re at it you might as well replace half the parts in there—plenty of bad transistors and blue caps.
    merlynski likes this.
  4. slayer44

    slayer44 AK Subscriber Subscriber

    Bethel, Vermont
    Agree with Eastpoint and Mark, my 828 did this exact same thing just the other day (popping with High and Low filters). Replace the Sanyo's and the 725's and you will be good. I lost the left channel also, which was due to bad 2sa725's. The JFETS I left alone and everything was back in working order. I recapped the entire board while I had it out just to be sure. Good luck!

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