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From: warren@cbnewsh.att.com (warren.a.montgomery)
Newsgroups: sci.electronics
Subject: Suggestions for an intermittent hum problem.
Keywords: 60 cycle noise audio
Message-ID: <1991Jan28.144723.16008@cbnewsh.att.com>
Date: 28 Jan 91 14:47:23 GMT
Distribution: na
Organization: AT&T Bell Laboratories
Lines: 21

My stereo receiver has developed an annoying problem.  Frequently,
when first turned on, it sounds a loud 60 cycle hum in the left
channel only.  Flipping the power on and off once or twice will
generally cure it.  Once or twice, the hum has appeared while the
equipment was on.  I have an undergraduate EE degree and have done
my share of amateur stereo repair, but hate problems like this
that are not repeatable and don't suggest anything obvious to me.
I also have no schematic and have been unable to locate the
manufacturer (Sherwood), but the unit is old enough that it's
built with discrete transistors and other parts and therefore
repairable.  60 cycle Hum suggests either a power supply problem
(ripple getting through a bad capacitor), but that would almost
certainly impact both channels, or noise on one of the input
signals (loose or improperly grounded plugs), but that should be
sensitive to the source of the audio (radio, tape, etc.), or the
volume control, which this noise isn't particularly.  Any suggestions?

-- 

	Warren Montgomery
	att!ihlpf!warren