03-06-2009, 04:12 AM
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Deity
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Join Date: Jul 2004
Location: Saint Regis Falls, NY, USA.
Posts: 5,306
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Thanked 148 Times in 143 Posts
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Almost all the time a 60 cycle hum is due to a bad ground. Banging on the unit sets up a vibration to anything that's loose. Filter capacitors are next. They are connected from the power supply [positive] to ground. Look for a metal can with a bulge somewhere in the can. This indicates a gassing condition. A short would blow a hole in it. They are a large value at a "Working Volts D.C."
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