Help diagnosing intermittant hum/buzz?

Discussion in 'AV Receivers' started by MikeHerbst, Feb 6, 2005.

  1. MikeHerbst

    MikeHerbst Stunt Coordinator

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    Hey everyone, hope someone can help me diagnose a problem I'm having recently with my Pioneer VSX-D509S receiver.

    Periodically (but not always), after the receiver has been on for some time, I get a buzz or hum throught the speakers.

    Based on all of the searching/reading I've done through the forum, I don't think its a ground loop. I'm guessing that (unfortunately) its a problem with my receiver that until recently has been perfectly reliable.

    Possibly pertinent facts about the behavior:

    1) This only seems to happen when the receiver is "warm" (i.e. been on for a while). The receiver itself has ample distance from other components, so it shouldn't be "overhot".

    2) It doesn't happen EVERYTIME the receiver is warm. (Not 100% repeatable)

    3) Happens on every input: TV, VCR, DVD, etc.

    4) Muting or changing the volume does not affect the level of the buzz. Whatever it is, its post-power stage in the amp.

    5) I've had the receiver for years, this only started happening recently, and there've been no changes in the wiring or setup of the media niche that correspond to the arrival of this problem.

    6) The first month or so of this problem, power cycling the receiver made it go away (for a while). Now once the hum starts, it mostly returns right away after the power cycle.

    7) The problem has been hard to troubleshoot because it doesn't happen all of the time, so unplugging components, etc. is hard to test cause/effect.

    8) The receiver is plugged into the surge protected but not-battery backed section of a UPS along with the DirecTiVo, DVD, VCR, and playstation. (Only the TiVo is battery backed). TV is on its own plug, but I believe its on the same circuit as the UPS.

    Do people even repair solid state amps anymore? Or is SOP just to junk it and replace these days?

    Thanks.
     
  2. Grant B

    Grant B Producer

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    Next time it starts buzzing
    1st try turning off the TV , unplugging and then disconnecting.
    No luck try all other components thats on.

    Is the buzz coming from all or 1 speakers.
    If one speaker try switching speakers and see if it goes with the buzz.
    Goes with the buzz it might be a speaker problem
    Those steps should narrow it down
     
  3. MikeHerbst

    MikeHerbst Stunt Coordinator

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    OK, been pretty busy so I haven't been watching much TV, so I haven't been able to play with this too much.

    Here's what I've found:

    1) Buzz is not actually through the SPEAKERS. It actually seems to be coming from inside the unit itself. Maybe a transformer going bad?

    2) The ONE time its done this since Grant B's post, I turned off the TV and the buzz seemed to FADE away. (i.e. it didn't click off with the TV, sort of faded out). Didn't come back right away when I turned the TV back on. Only one cycle of this test, so I hate to draw any conclusions yet.

    Then I had to go to work. I'll play with it more, but I'm starting to think there's maybe a Capacitor going bad that's coupling a transformer to ground or something. Had this happen a lot on old tube amps I use for playing guitar...

    As I said, I'll play with it more.
     
  4. Chu Gai

    Chu Gai Lead Actor

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    So it seems as if the buzzing is coming from within the receiver. There's a couple of approaches you can take Mike, with the usual caveats of being careful working around electricity. You can remove the cover of the receiver and then attempt to get the buzz to come back. You might find then that it's easy to locate the origin. If not, you can try putting one end of a flexible tube to one ear and then moving the open end around the receiver to identify the origin. You might even be able to find a kid's plastic stethoscope! The tube approach is sometimes used by mechanics to locate a sticking valve on a car. Anyways, if it's the transformer, then it probably has screws or nuts to keep it in place. Those might be loose and a slight turn (turn the unit off and wait for things to discharge!!) will make all well again. OTOH, there might be rubber washers or grommets that have gotten hard or just simply decomposed due to the prolonged exposure to heat and just replacing them does the trick.
     
  5. Grant B

    Grant B Producer

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    Does it have a grounding post on the back?
    What about the power cord and the outlet it plugs into?
    The old 3 pin adapter into a 2 prong socket could be a culprit
     
  6. TjienPing

    TjienPing Auditioning

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    Is there any update to this issue?
    I have the same exact problem, except that my D509S buzzes very often now, pretty much everytime I turn it on. It used to be intermittent like the original problem described..

    The cost of fixing it via service repair guy is quite expensive.. so I'm thinking of fixing it myself, but not sure what I'd be looking at.. By the way, I found the service manual. Just google for "d509s service manual", found the link from eserviceinfo

    Does buzzing sound typically comes from a bad capacitor?
    Thanks guys!
     
  7. CraigF

    CraigF Cinematographer

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    If the buzz is electronic, and it wasn't there before, then yes it's probably a dying/dead cap, electolytics can/do go bad over time.

    If it's a mechanical buzz, then likely you just need to tighten some transformer mounting screws LOL. I don't know the guts of your model, but toroidal transformers are typically held by just one center bolt and it's not too unusual for them to buzz after some time...if you have one of those.

    I think the previous guys covered everything I could think of. Need more exact details for "remote servicing"...
     
  8. TjienPing

    TjienPing Auditioning

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    Thanks a bunch for the reply Craig. I think I fixed the problem. It was the big power transformer (part no: ATS7264) inside the receiver that was vibrating. The buzzing was mechanical afterall. The transformer is tied down using 4 screws securely.. but somehow, the bottom part of the transformer was vibrating against the case, causing the buzzing noise. I fixed it by inserting a couple of layer of teflon tape, which should be non-flammable and can withstand high temperature, at the bottom of the transformer.
    If I listen carefully close to the receiver now I can hear a slight hum, but much better than the loud buzzing sound from before.

    I have a couple more questions:
    1. Is transformer humming "normal" ? Or do I have something to worry about like it's going to die or catch fire?
    2. Are there better ways to fix this?
     
  9. CraigF

    CraigF Cinematographer

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    Well, all large transformers will hum to some degree when loaded. Generally it's not noticeable with HT gear like amps and AVRs, but I have never stuck my head right in when they're well loaded. What you don't want is the plate/case the tranny is mounted on to resonate and amplify it. So an isolated mounting should do it, but as others said they can dry out/harden from heat over time. I have even heard a rack shelf resonating from a transformer vibrating somewhere before.

    The only time I have noticed an HT tranny really buzzing *loudly* is when it was assymetrically loaded. This means the whole core was not loaded evenly, perhaps one winding being unloaded due to a failure, or to another winding being overloaded...depends how the windings are spaced on the core. This type of buzzing will NOT be removed by simple mounting isolation, it is eddy currents in the core etc. causing it, so I think you are free from a more serious problem.

    If the tranny is easy to remove, some rubber or softish plastic mounting bushings should last a while.
     

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