asterisk users - Feb 2006 - Faint background noise/crackle on FXS port on TDM400P

Hi, I have had this issues for ages but have ignored it, but my handsets 
get  faint background crackle on the FXS port. When I connect the handset 
directly into my PSTN, it goes away complete, so I am generating this from 
somewhere in my asterisk box. I get it immediately when the phone goes 
off-hook and it stays through the dialing and call progress.

I can't think of any other devices generating any interference along the 
line anywhere between the FXS port and my phone handset.

Any ideas ?

regards

Mark
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> Hi, I have had this issues for ages but have ignored it, but my handsets
get  faint background
crackle on the FXS port. When I connect the
> handset directly into my PSTN, it goes away complete, so I am generating
this from somewhere in
my asterisk box. I get it immediately when the
> phone goes off-hook and it stays through the dialing and call progress.
> 
> I can't think of any other devices generating any interference along
the line anywhere between
the FXS port and my phone handset.
> 
> Any ideas ?
Some things to check........

- put a voltmeter across tip-ring on the phone connected to the TDM card
  to see if the 48 volt DC is varies.
- ensure the 12 volt connector for the card is solidly connected
- check for shared interrupts (TDM card should be on an interrupt by itself;
  hundreds of postings in the archives on how to check, etc.
- call digium support

Hi, more info, it seems that I am only getting the background noise on one 
of the two FXS ports on my TDM400P

One port is perfect, the other is crackly. I ran a bunch of tests, checked 
interrupts etc.

Anyone seen this issue before ? Both ports are configured identically.

Mark
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