Path: utzoo!news-server.csri.toronto.edu!cs.utexas.edu!uunet!mcsun!ukc!ox-prg!mason
From: mason@robots.ox.ac.uk (Ian Mason)
Newsgroups: comp.sys.ibm.pc.hardware
Subject: XT Power supply high-frequency noise?
Message-ID: <1463@culhua.prg.ox.ac.uk>
Date: 14 Mar 91 12:01:18 GMT
Sender: news@prg.ox.ac.uk
Organization: Engineering Science Dept, Oxford, UK.
Lines: 30
Originator: mason@cymbeline.robots

I am posting this for someone. However he reads this
(comp.sys.ibm.pc.hardware) newsgroup.

-------------------forwarded message--------------------

I have bought a 2nd hand XT with a 135W power supply, and then
upgraded the motherboard to a 386SX-20MHz. At the moment it is running
in a configuration of a Hercules-compatible graphics hard, a floppy
disk controller (5.25in 360k drive), and a MFM 20M Seagate hard drive.

The problem is that the power supply is giving out high-frequency
noise when idle. i.e. when neither the hard disk or the floppy disk
are in use. e.g. The noise dies when I do a dir on a:. [There was no
such noise with the XT board.]

Can anybody tell me what is the problem and cure? I understand that
the noise could well be from the switching elements of the switch-mode
power supply. It doesn't seem like a not-enough-power problem, since
it only happens when idle. Any hints welcome.

Thanks in advance.

Delman.
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   Delman Lee
   Dept. of Engineering Science,
   Oxford University,
   Parks Road,                   Internet & BITNET: delman@sun.eng.ox.ac.uk
   Oxford, OX1 3PJ, U.K..                    JANET: delman@uk.ac.ox.eng.sun
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