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Weird problem with a PA head, any theories?

Discussion in 'Amp Central Station' started by Mr Perch, Oct 18, 2013.

  1. Mr Perch

    Mr Perch Tele-Afflicted

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    My band has an ancient Sunn PA head that has been very reliable. Last week, one of the clubs asked if they could play music on an Ipad through it during our breaks. We said "fine," and used the "tape in" RCA inputs. But then trouble started. We couldn't get sound from the PA when we resumed our set. We fiddled with the main volume and the thing began to work again.

    Then, last night, we turned it on and nothing happened. We thumped it and twisted knobs, and suddenly it began to work again. Then toward the end of the first set, it quit. We discovered that by turning it off and then back on, we could revive it. We had to do that again later in the night.

    This seems very mysterious. It doesn't seem to be a potentiometer problem. I sprayed contact cleaner into the main volume knob and it had no effect. Do you have any idea at all what might be causing this?
     
  2. chrisgblues

    chrisgblues Tele-Afflicted

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    If it has a fuse, try replacing it. Cheap first step.
     
  3. Jakedog

    Jakedog Telefied Ad Free Member

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    If it were mine...

    First step is buy a new, reliable PA head. Something with a warranty, that you can count on. They are more affordable than ever right now. You can probably get something with more, and cleaner power, pretty cheap.

    Step two - take the Sunn in for service. If the problem is more than a hundred bucks, junk it. It's a paper weight. If you can get it fixed cheap, keep it on hand as a backup / practice space PA.

    You might not want to hear this, but that's what I call a piece of " Bic lighter" gear. You use it til it stops working, enjoy it thoroughly, make money with it, then toss it out and get a new one.
     
  4. Mr Perch

    Mr Perch Tele-Afflicted

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    I sort of suspected that. I owned a Fender Super Champ XD that was under warranty. When it went south, the way they honored the warranty was to give me my money back.
     
    Last edited: Oct 19, 2013
  5. Mr Perch

    Mr Perch Tele-Afflicted

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    Could a bad fuse cause the behavior I described?
     
  6. RockerDuck

    RockerDuck Friend of Leo's

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    No. Sounds more like a faulty transistor that you let music pass thru, also shared with the output channel. Solid State components tend to wear out of their tolerances. Probably easy to repair, until the next one goes. I had Peavey PA over 30 yrs. I loved the tone and told everyone how reliable it was, then I turned it on one day and it bit the dirt that fast. Not worth the repair. Nor will I buy one that old used. Time for a new one. I had to get a 600 watt PA to do the same volume as that old 100 watt Peavey.
     
  7. syrynx

    syrynx Tele-Afflicted

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    Homing in on the words "ancient" and "very reliable," as well as the thumping and knob twisting, it sounds exactly like an intermittent/dirty spring tension connection. I'd clean all of those I could find before spending any money: All input/output jacks (including effects return), pots, reverb tank connections, etc.

    With any old electronic gear, this is always my first step.
     
  8. wetblankit

    wetblankit TDPRI Member

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    I agree with a few of the posters. Transistor or faulty connection is most likely since knob fiddling gets it working.
     
  9. gearhead63

    gearhead63 TDPRI Member

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    I'd be sure to clean the on/off switch also. May have a dirty contacts making intermittent contact or low voltage.
     
  10. jtees4

    jtees4 Tele-Afflicted

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    YES....most likely the cause. I'd open it and spray contact cleaner real heavy on all the pots and switches. Cheap and easy way to begin.
     
  11. Mr Perch

    Mr Perch Tele-Afflicted

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    Can anyone point me to an online resource that will guide me in doing that safely? I have seen references here on tdpri to the dangers of touching capacitors, etc. I wouldn't know a capacitor from a B-bar.
     
  12. GigsbyBoyUK

    GigsbyBoyUK Friend of Leo's

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    As long as it's a solid state amp and you turn it off and unplug it you will be safe. There is no real need to actually touch any components anyway.

    Don't use too much contact cleaner - just a little squirt in the pots and then rotate the knobs a few time is a good starting point. Ditto for switches.

    Also just look around inside the thing and gently touch components with a toothpick or something to see if there is an obvious broken resistor leg or something as simple.

    After that, see if an expert can take a look. I have had a few old bits of gear go glitchy like this and for not too much outlay an electrical engineer has been able to quickly find and fix it. Sometimes though they fall into the 'more trouble that it's worth' category.
     
  13. Mr Perch

    Mr Perch Tele-Afflicted

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    Do you think that plugging the Ipod into actually triggered the problem, or was it purely a coincidence? We never had a problem before that.
     
  14. buckfuzzard

    buckfuzzard Tele-Meister

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    Just coincidence.......

    maybe a bad solder joint
     
  15. String Tree

    String Tree Doctor of Teleocity Ad Free Member

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    I'm with Jakedog, get a new Board.

    This one has heat issues, one thing is going to lead to another until it fails for good.
     
  16. syrynx

    syrynx Tele-Afflicted

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    There is absolutely no evidence that this unit has heat issues.
     
  17. Mr Perch

    Mr Perch Tele-Afflicted

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    As a matter of fact, I just picked up a Carvin this morning. But I hope to squeeze a bit more life out of the Sunn.
     
  18. vjf1968

    vjf1968 Poster Extraordinaire

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    Obviously clean every contact and pot. Also get a can of compressed air and blow out any residue.
     
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