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HELP! Used QSC PLX making noises ...

Discussion in 'Amps and Cabs [BG]' started by misterk73, Oct 22, 2003.


  1. misterk73

    misterk73

    Apr 11, 2002
    Flagstaff, AZ
    I just picked up a used QSC PLX sight unseen and am unfortunately having some problems. Basically, I want to know if I should be pissed and try to get some or all of my money back or if I can deal with these things on my own. Any ideas for diagnosing and fixing would be appreciated.

    1) Problem #1: Channel 1 crackles when I turn the control knob and there's a bass signal present.

    2) Problem #2: Every so often -- every 15 minutes or so? -- there's a sharp pop. It reminds me of the noise you get when plugging into a turned-on amp or maybe even the crackling of a cord. It's not especially loud -- there's no clipping or anything -- and it seems to happen whether there's a bass signal present or not.

    I didn't notice problem #2 until yesterday evening after having already used the amp for a few relatively trouble-free days both solo and at band practice. The only change I can think of is that I hung an afghan on the wall behind the rack case -- could this actually be a static electricity problem caused by the blanket and/or carpeting in the room? What else might be causing this? More importantly, what can I do about it?

    Thanks for your input...
     
  2. misterk73

    misterk73

    Apr 11, 2002
    Flagstaff, AZ
    Things that go bump in the morning...
     
  3. pbd

    pbd Commercial User

    Jul 17, 2003
    Metro Detroit
    owner Procables N Sound
    Sounds like dirty pots to me. Dependant on the last owner you could have anything floating around in there. Unplug it and open the case. get a small vacuum or can of compressed air (both need to be low volume of movement).When it's cleaned out put the cover back on. Pull your knobs and clean them with pot cleaner or isoprophl alcohol. Then run them back and forth a bunch of times to clean the debris off the internal parts. Clean the plugs/jacks with compressed air (low volume) and by running the jack in and out a few times to clean the contacts. A little cleaner can be used as well. Then try using it again. you may need to clean the pots a little more. Smoke and pet fur/dander are killers to equipment!
    good luck, and remember not to touch anything inside the amp case. Ouch!:D
     
  4. misterk73

    misterk73

    Apr 11, 2002
    Flagstaff, AZ
    Cool. Thanks. That's the kind of info I need. Do you think dirty pots could cause the intermittent popping as well as the cracklin when I turn the gain knob?

    What threw me about the popping noise is that is doesn't seem to have an action -- playing, turning a knob, etc. -- associated with it. (It's a glitch that doesn't seem to discriminate.) Weird...
     
  5. marc40a

    marc40a

    Mar 20, 2002
    Boston MA
    I'm not sure about the pot but the intermittent crackling noise is your ribbon cable. There was a defective run of them a few years ago.

    If you call QSC and give them your serial they'll take care of it.
     
  6. misterk73

    misterk73

    Apr 11, 2002
    Flagstaff, AZ
    Thanks for the input, guys. I'll definitely check the serial number when I get back to my practice space and try to deal directly with QSC -- I've been calling local shops about servicing and haven't liked their prices or turnaround times. (I've also contacted the guy who sold it to me and requested a small, partial refund to help defray servicing costs. Not sure if he'll bite, but it's worth a shot.) Thanks again for the tips and info ...
     
  7. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    If the amp was made before July 1999, it could have suspect ribbon cables. The first four digits of the serial indicate the month and year of manufacture--for example, 0401xxxxx = April 2001. So you would be looking to see if your amp is 0699 or earlier.

    If your amp falls in this time frame, we'll replace the ribbon cables free of charge and even pay the shipping to the factory. And we'll send you a free box if you don't have anything to ship it in.

    Just call 1-800 QSC AUDIO or e-mail tech_support@qscaudio.com and give your name, shipping address, phone number, and the amp's serial number, and mention that it's a ribbon cable update.
     
  8. misterk73

    misterk73

    Apr 11, 2002
    Flagstaff, AZ
    Thanks, Bob! I'll be checking the serial number tomorrow night and will probably be sending the amp in for servicing regardless...
     
  9. misterk73

    misterk73

    Apr 11, 2002
    Flagstaff, AZ
    Sweet! It looks like the serial number qualifies me for a ribbon-cable update.

    (Hopefully, QSC will be also be willing to take care of that dirty pot and maybe clean the amp out as long as they have it onsite.)

    Regardless, thanks to everyone for the input and assistance!

    This makes me happy ... :D
     
  10. Hey lushfreak, for future reference it's called "trouble shooting" not diagnosing....... that's what a doctor does.

    [​IMG]
    Treena
     
  11. misterk73

    misterk73

    Apr 11, 2002
    Flagstaff, AZ
    Right. Some of my best friends are doctors, so I've picked up all kinds of dirty language from them.

    Thanks for the tip. (Love your smilies, BTW!)
     
  12. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    No problem. We clean the amp out as a matter of course (it makes the amp easier to work on, besides). It would be a good idea to mention the dirty pot when you contact us for the RA, and also include a note mentioning it when you send the amp in. That'll alert the tech or engineer who works on it to take care of it; it probably just needs a shot of cleaner.

    Let us know also if you don't have the original factory box and packing material to ship the amp in; we'll send one to you for free.
     
  13. misterk73

    misterk73

    Apr 11, 2002
    Flagstaff, AZ
    Good to know! Thanks again, Bob!
     
  14. Sufenta

    Sufenta Trudging The Happy Road of Destiny

    Mar 14, 2002
    The Signpost Up Ahead.
    Ah, another happy TalkBass ending:)

    All of this happy talk is giving me GAS for a new PLX.
     
  15. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    It only applies in the USA, because we handle the warranty services for US-sold product ourselves. In other countries, our authorized distribution agents handle their own respective warranty arrangements. In Finland, that would be EM Nordic Oy (+358 9 825 45 60). Contact them about getting your ribbon cables updated.