PSN-L Email List Message

Subject: Re: Noise problems
From: Bob Smith bobsmith5@........
Date: Mon, 07 Aug 2000 09:04:43 -0400

There have been a number of recent posts here regarding
noise problems with a new computer.

I am reminded of a problem years back with a trusty old
386SX system that had given me excellent service for a
number of years.  It was eventually replaced with a 486DX
system in the pursuit of improved performance (to carry all
the overhead of recent releases of WinDoze).

The old 386 was then pressed into service in my amateur
radio station to create a TCP/IP node and server system on
the local amateur packet radio links.

When I installed the packet radio modem card, I could not
get it to work because it thought that there was a signal on
the air all the time and, thus, would never switch to
transmit mode.

To make a long story short, I found that the +5V power in
the old 386SX was covered with random noise like crud that
was getting into the packet modem chip and creating false

A new orignal equipment power supply was purchased and
installed, same problem!

The problem was traced to lack of loading on the power
supply that was created when most of the peripheral boards
were removed and moved to the new 486DX system.

The solution was to install a couple of used peripheral
cards in spare slots untill sufficient load was created to
stabilize the power supply.

Therefore, I strongly recommend that the gentleman with the
noisy computer get a good scope on the power supply lines
and look for excess noise.  Expect to see some residual
switching noise, but anything excessive such as >100 mv P-P
should be suspect.

	Good luck, Bob Smith


---------  Avoid computer viruses  --  Practice safe hex 
 * * Specializing in small, cost effective embedded control
systems * *
Robert L. (Bob) Smith			Smith Machine Works, Inc.
internet   bobsmith5@.............. Lumlay Road
landline   804/745-1065	                Richmond, Virginia

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