Path: utzoo!censor!geac!torsqnt!news-server.csri.toronto.edu!cs.utexas.edu!samsung!rex!ames!dftsrv!chris
From: chris@endgame.gsfc.nasa.gov (Chris Shenton)
Newsgroups: comp.dcom.modems
Subject: T2500 has nasty hum
Message-ID: <CHRIS.91Jan29153400@endgame.gsfc.nasa.gov>
Date: 29 Jan 91 20:34:00 GMT
Sender: news@dftsrv.gsfc.nasa.gov
Reply-To: uunet!media!thanatos!steve=
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Lines: 31

My recently purchased a Telebit T2500 appears to put a nasty
hum   on the   phone   line.  Briefly, when    there  are no
connections to the modem except the phone line, all is fine.
If the  power xformer and/or the RS-232  cable is hooked up,
the hum appears.  Turning off the  power  switch on the back
of the modem does not change anything. If  I place the modem
on the line and  "listen  in" the  hum is  unbearable, which
makes me think that it  is coming from the  analog circuitry
inside.

Further  inspection  of   the [AC]  wiring  in the  vicinity
revealed that  the outlets in use  were  ungrounded. I moved
all of the line plugs from  the computer, modem, and monitor
into the same outler  strip, which helped a little. Plugging
the strip into a grounded outlet helped a bit more,  but did
not eliminate  the  problem. Telebit  tech  support [one day
turn-around by e-mail, BTW  ;-)] had no further  suggestions
beyond grounding.

Before  I make the assumption  that something is broken, I'd
like to hear the experiences of other  T2500 users. Does/did
yours have  this problem, and  if so, how did you  solve it?
Of course, any suggestions from telecom-guru-land are always
welcome.

Thanks in advance.

Steve

--
chris@asylum.gsfc.nasa.gov, ...!uunet!asylum.gsfc.nasa.gov!chris, PITCH::CHRIS