From: Kevin McMurtrie
Subject: Re: Strange failure mode in switchmode power supplies: Followup
User-Agent: MT-NewsWatcher/3.2 (PPC Mac OS X)
Date: Fri, 20 Sep 2002 07:52:54 GMT
NNTP-Posting-Date: Fri, 20 Sep 2002 00:52:54 PDT
Put a sacrificial system on an extension cord and operate it at a
neighbor's house with your power. Now operate it at your house with a
neighbor's power. Anything?
Maybe your house is getting blasted with microwaves. They don't show up
on a scope but they rectify in some semiconductors to create a bias
current. How's your UHF TV reception?
Speaking of scopes, post a link to a picture of what the SMPS is doing.
In article ,
firstname.lastname@example.org (Peter Gutmann) wrote:
>A few months back I posted a message about strange failures in assorted
>switchmode power supplies in computers, printers, routers, etc etc. Various
>people offered suggestions, and I've been trying those out (along with
>anything else I can think of) to try and find the cause of the problem. Just
>to recap (from the original post, page down to get to the new stuff):
> The immediately obvious symptoms are that any SMPS plugged into the power in
> my house starts producing large amounts of high-frequency (ultrasonic)
> switching noise, both audibly and in its DC output. At 50W it's mostly
> inaudible (but enough to cause the usual unpleasant effects of ultrasonics
> if you sit next to it for awhile), at 100W you can sense it easily (although
> not necessarily directly hear it), and at 200W it's so bad you can't stand
> being in the room for more than a few minutes without feeling ill.
> What's bad for humans is even worse for any elecronics sitting downstream,
> so far this problem has caused about $2K of damage in assorted computers,
> routers, etc etc (the damage is pretty spectacular, one device which failed
> was an online UPS which I'd been using to protect the PC downstream, every
> high-speed switching component in it had been fried).
>The things I'd tried originally:
>- Check neighbour's houses (nothing, only this one).
>- Check times (it's present 24/7)
>- Check for wiring problems (eg ground & neutral reversed, nothing)
>- Check the power quality with a line analyser (nothing unusual apart from the
> expected irregular fluctuations, spikes, etc)
>- Check the (input) power with a scope (nothing, with the exception of about 5V
> p-p ripple at maybe 1kHz on the sinewave peaks which appears for about 5s and
> vanishes for 30-60s, it's not continuous so I doubt it's the problem)
>- Get the power company to check the power into the house. "OK, it's about
> 240V, everything looks fine, connections look OK, sorry, that's all we can
> do" (well, it was worth a try).
>- Assorted line filters, power conditioners, and anything else I could get my
> hands on (no effect).
>- Run a direct line from the power board where the power enters the house to
> the affected gear (no effect).
>- Physically disconnect the power to everything else in the house except the
> single line going straight to a sacrificial PC (no effect).
>- Get the same power company (after several months of arguing and a written
> complaint) to switch the house over to a different phase in case there's
> something like a large reactive load on the same phase causing problems (no
>- Get a new earth fitted in case the existing one (~25 years old) had corroded
> through about 10cm below the surface (no effect).
>- Connect a large linear load in parallel with the SMPS (no effect).
>- Took readings at various locations around the house and in neighbouring
> houses with a scope (much newer than the clunker I used earlier, and a
> portable LCD one you can hold in one hand... drool): A generally clean
> sinewave with some (very slight) odd-order harmonic distortion in the
> 150-300Hz range, but nothing serious, and not much different from either the
> neighbouring houses or the power in the house of the person I borrowed the
> scope from (which is miles from here). In other words, nothing obviously
> different from locations where there was no problem.
>- (I wanted to see what I could find on the line with a spectrum analyser, but
> the only one I could get my hands on starts at 50kHz and doesn't have a HV
> probe, and the owner wasn't at all enthusiastic about letting me put one
> together myself).
>- After much searching tracked down a ferroresonant transformer which is
> probably about the most you can do to filter (or regenerate the signal from)
> a power line (I know there's some folklore out there about these upsetting
> some SMPSes, but I never had any problems with several sacrificial systems
> I tried) (no effect).
>This means that either it's something incredibly insidious in the power which
>doesn't appear on a scope and can walk through a ferroresonant circuit, or it
>isn't anything related to the power at all. Unfortunately I can't even blame
>whatever's causing this on power problems any more now, and there's nothing
>left... at best I can handwave some sort of EMI issue, but (a) I'm nowhere
>near any source of this and (b) I'd have thought an earthed metal box (SMPS
>case) inside another earthed metal box (PC/router cases) would offer at least
>some amount of shielding (modulo the power cord and other impromptu aerials
>provide a means of access, obviously). I really don't want to sell the house
>to fix this... does anyone have any other ideas? Anything I missed? Exorcism?