I have a ax-550 and the input switch was not making proper connection for years. So I took the amp cover off and found the metal cover over the switch. I then pried the end cover up enough to spray a pile of contact cleaner inside as I moved the switch . After it was dry reassembled and voala...I now can listen to pink Floyd with out one side all static.
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if the time ever comes you can't see it, you can lay on your back and do it from underneath.
