power switch causing crackling sound

Discussion in 'Amps and Cabs [BG]' started by billoetjen, Feb 18, 2010.

  1. Ampeg BA110 combo.
    After at least six years of daily use, my practice combo is having some minor annoying, persistent problems. The main one is a crackling sound that goes away entirely if I press lightly down on the power switch (rocker switch mounted on the top side of the amp chassis). All the knobs and switches are mounted on the top, which is a long-term problem as far as collecting dust, etc. Here's a pic


    the power switch is all the way on the right. :help:

    Anyway, can anyone recommend a fix such as a cleaning solution or something that can save me from having to replace the switch? I really need this amp, it's my daily workhorse and even holds its own in band practice.

    Thanks in advance,

  2. fdeck

    fdeck Supporting Member Commercial User

    Mar 20, 2004
    Madison WI
    HPF Technology LLC
    Whatever you do, make sure you replace the switch soon. If a power switch is dodgy, it will heat up and eventually give out altogether. That's a process called "thermal runaway."

    A rocker switch is unlikely to be fixable by contact cleaner. It might be a snap-in unit that is relatively easy to replace. But don't attempt this unless you are qualified to do it safely.
  3. Hey, thanks Fdeck.

    It seems to be getting worser and worser.
    Gonna look up where I can get a switch to replace that.
  4. BassmanPaul

    BassmanPaul Inactive

    Sorry Fdeck but that's not thermal runaway. Thermal runaway happens when a SS device is run outside of its safe operating area. As it passes current the device heats up and its internal resistance drops. This causes it to pass more current which means it gets even hotter. This cycle continues until the device fails.

    In a power switch with bad contacts the resistance increases causing a voltage drop. this will eventually burn out the switch. I agree fully that the switch needs to be replaced before it can cause burning.

  5. Went to Radio Shack tonight, barely made it in time before they locked the door. Found a similarly spec'd switch but its base was thread-on, therefore a little wider than the original narrow, bayonet mount switch. Also the lugs were too small to fit the original connectors so I had to solder directly. The most anxious moment was using my Dremel with sanding wheel to make the existing opening fit the new base.
    While at it, I disassembled the power cord through-chassis stress relief because the outer insulation was pretty far gone. Pulled about 3/4" of original cord into the housing before reassembling.
    Everything went back together with no parts left over.
    Still a trace of hum, but gone is the crackling!

    Tanks, Everyone