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"waves" in circuit boards

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by jherman, Aug 19, 2006.

  1. jherman

    jherman Member

    Messages:
    62
    Joined:
    Jul 19, 2006
    Location:
    AZ
    Hello group. I have a Fender Showman that has been out of its cabinet for a while awaiting a recover. I noticed that the circuit board has pushed up between the mounting screws causing "waves" or "buckles" or whatever you'd like to call them. It seems to be putting undue stress on the bare wires that go towards the pots.
    I pulled the chassis fom my blackface Super and Deluxe (both in mid-project status) to compare. They both had some curving in beween the mounting screws, but nothing inside of them looked pulled or stretched like the Showman.
    I tried pushing down in the center of the raised area, but the board material is hard and I didn't want to risk breaking it.
    Every picture I could find of an AB763 chassis is straight down so it's hard to tell if this rolling between the screws is normal or something to be concerned about.
    These amps have been stored in the same bedroom. Right now is when we 're going from extremely dry and hot to rainy and humid. Could the weather have an effect on the board material?
    I appriciate any and all answers, comments, wise cracks, etc. Thanks
     
  2. bob-i

    bob-i Member

    Messages:
    7,810
    Joined:
    Oct 16, 2005
    Location:
    Central NJ
    The waves are normal, many of these eyelet boards do that with age, but the pulling on the wires is an issue. You may have to replace some wires if you can't adjust the board.
     
  3. TheAmpNerd

    TheAmpNerd Member

    Messages:
    1,062
    Joined:
    Sep 23, 2004
    Location:
    Tejas
    What Bob said.

    AND

    I wouldn't bother trying to flatten out the board.

    If you have a hot
    enough iron (100 watter) then replace those ground wires
    with longer buss wire.

    (While you may get by with a colder iron on this
    it isn't worth the hassle. You'll sit there and heat
    it up and heat it up and heat it up some more,
    it just may start to run and out comes the old wire.

    Then, you get the joy of installing the new wire
    and hope you do a proper gound joint on that
    chassis.

    It would be cheap insurance to drop it by your techs
    and have him do it with a proper iron.)

    If you don't have a hot enough iron,
    then you can rig it by doing the following:

    1. Desolder and clean from the eyelet.
    2. Splice in a short buss wire or standard wire to
    the desoldered side.
    3. Heat shrink the new joint.
    4. Then resolder it to the eyelet after cleaning out
    all the old solder from the eyelet joint.
    5. Plug and play.
     
  4. jherman

    jherman Member

    Messages:
    62
    Joined:
    Jul 19, 2006
    Location:
    AZ
    Thanks for your answers. I'll put longer ground wires on before it goes back in its cabinet. The others (to the pre-amp tubes) have lifted some but they still have plenty of slack.
     
  5. Fretts

    Fretts Member

    Messages:
    365
    Joined:
    Nov 20, 2003
    Location:
    Santa Monica, CA
    Yes, that buckling is an unfortunate side effect of that fiberboard material. My '64 BFSR did not work when I got it and it had curves in it that looked like the roller coaster at Magic Mountain. Eventually I found exactly what you are talking about... the curves had pulled one of the ground wires so hard that it had snapped in midair, but they were "almost" still touching. It looked fine if you were just looking things over. If you looked REALLY close, you could see that there was a tiny airgap where the wire had snapped. So I did try to press the board back again, no luck there.
    I did do just what The_Amp_Nerd says, I replaced the ground wire with a longer one. Now it works fine and sounds great thanks to that repair, a cap job and about 50 other little cleanup chores.
    I understand that the vulcanized fiberboard can absorb moisture and that's what causes it. In really humid places, like Florida where I grew up, it can get so bad that the amps will squeak, hiss, crackle and pop for no apparent reason and it is the fiberboard holding so much moisture that it is semi conductive which wreaks havoc with the circuitry.
     

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