RFI from new PC

  • Thread starter Thread starter Thomas J. Andrews
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Thomas J. Andrews

I bought a new bargain-basement desktop PC online about six weeks ago.
It uses a Biostar M7VIG-Pro motherboard, 256M of PC2100 DDR RAM, Athlon
XP 1900+ processor, and a Maxtor 40G 7200rpm HD in a mid-tower ATX case
with a 400 watt power supply. I installed my own cd burner and another
HD, an old Maxtor 8.4 G.

From day 1 this outfit has produced RF on the AM radio band, injecting
it into the AC line and to the phone line through the serial port and my
external modem. The noise is bad enough to drown out a moderately-strong
AM station. The RF appears as soon as the power gets to the computer and
the master switch on the power supply is switched to "on". The computer
itself doesn't have to be "on" and the level of noise doesn't change
when it IS "on". Changing wall outlets and /or moving to a different
room make no difference. The computer seems to be working properly. My
old PC, an aging IBM PC300GL, produces NO noise, even when connected to
the same outlet and peripherals (modem, monitor, keyboard, mouse, etc.)
Oh, and the cd burner and second HD were pulled from the IBM, where they
produced no noise.

At first we thought it was the power supply, but a builder-provided
replacement made no difference. A replacement motherboard reduced the RF
by a very small amount, essentially making no difference. Running the
computer and preipherals through a surge suppressor with an RF filter
reduces the RFI heard in the radio, and placing a KY AM-1 filter in the
phone line reduces it even more. Even with all that the RF is still
quite audible in the AM radio, though now at (barely) tolerable levels.
I've just purchased a line conditioner on Ebay, and I hope that may
finish cleaning things up.

The filters are only a band-aid solution, at best. I'm still wondering
where that RF is coming from, and what it is doing to the various
components in the system, even with the filters in place. My prime
suspect is still the power supply, even though it's been replaced.

Does anybody have any ideas?
 
I bought a new bargain-basement desktop PC online about six weeks ago.
It uses a Biostar M7VIG-Pro motherboard, 256M of PC2100 DDR RAM, Athlon
XP 1900+ processor, and a Maxtor 40G 7200rpm HD in a mid-tower ATX case
with a 400 watt power supply. I installed my own cd burner and another
HD, an old Maxtor 8.4 G.

From day 1 this outfit has produced RF on the AM radio band, injecting
it into the AC line and to the phone line through the serial port and my
external modem. The noise is bad enough to drown out a moderately-strong
AM station. The RF appears as soon as the power gets to the computer and
the master switch on the power supply is switched to "on". The computer
itself doesn't have to be "on" and the level of noise doesn't change
when it IS "on". Changing wall outlets and /or moving to a different
room make no difference. The computer seems to be working properly. My
old PC, an aging IBM PC300GL, produces NO noise, even when connected to
the same outlet and peripherals (modem, monitor, keyboard, mouse, etc.)
Oh, and the cd burner and second HD were pulled from the IBM, where they
produced no noise.

At first we thought it was the power supply, but a builder-provided
replacement made no difference.
Click to expand...

.... but, was it the same make/model? Sometimes the same junk generic
models will wear different labels, even have slightly different
exterior metal casings. I suggest a name-brand quality unit with
Active PFC. Post the make/models of those you have/had please, so we
can be sure to avoid them.

A replacement motherboard reduced the RF
by a very small amount, essentially making no difference. Running the
computer and preipherals through a surge suppressor with an RF filter
reduces the RFI heard in the radio, and placing a KY AM-1 filter in the
phone line reduces it even more. Even with all that the RF is still
quite audible in the AM radio, though now at (barely) tolerable levels.
I've just purchased a line conditioner on Ebay, and I hope that may
finish cleaning things up.

The filters are only a band-aid solution, at best. I'm still wondering
where that RF is coming from, and what it is doing to the various
components in the system, even with the filters in place. My prime
suspect is still the power supply, even though it's been replaced.

Does anybody have any ideas?
Click to expand...

I wouldn't worry about that effecting the system as much as excessive
ripple or if/when the power supply fails, what safety & shutdown
features it has.
 
Thomas J. Andrews said:
I bought a new bargain-basement desktop PC online
Click to expand...
mid-tower ATX case with a 400 watt power supply.
Click to expand...
From day 1 this outfit has produced RF on the AM radio band,
Click to expand...
The RF appears as soon as the power gets to the computer and
the master switch on the power supply is switched to "on".
Click to expand...
Changing wall outlets and /or moving to a different room make no
difference.
My old PC, an aging IBM PC300GL, produces NO noise,
Click to expand...
At first we thought it was the power supply, but a builder-provided
replacement made no difference.
Click to expand...

What brands of PSUs are these?

I had two cheap PSUs that did the same thing, and just as in your case
it didn't help to move the computer or try different wall outlets.
But the problem was definitely caused by RF coming out the AC cord
because after I installed choke-capacitor RF filters in them they
became dead silent, even when used only a few feet from the AM radio
and plugged into the same wall outlet. I had tried a Belkin surge
protector labelled as containing an RF filter, but it didn't help at
all, probably because its filter was nothing but a single capacitor,
with no chokes to actually block the RF. In one of the PSUs I was
able to simply add the missing filter capacitors and chokes to the
circuit board because it had been designed for them, but with the
other PSU I had to remove the power cord receptacle and replace it
with a combination receptacle/filter. Adding the latter may be
impossible to do safely because it's 2-3" long and may not clear other
components.
 
Thomas J. Andrews said:
I bought a new bargain-basement desktop PC online about six weeks ago.
It uses a Biostar M7VIG-Pro motherboard, 256M of PC2100 DDR RAM, Athlon
XP 1900+ processor, and a Maxtor 40G 7200rpm HD in a mid-tower ATX case
with a 400 watt power supply. I installed my own cd burner and another
HD, an old Maxtor 8.4 G.

From day 1 this outfit has produced RF on the AM radio band, injecting
it into the AC line and to the phone line through the serial port and my
Click to expand...
<snip>

Confirm that it's grounded propery...is your outlet *really* grounded?
 
philo said:
Confirm that it's grounded propery...is your outlet *really* grounded?
Click to expand...
I even tried running a seperate wire from the ground tab of an adapter
to a galvanized water pipe that leads out underground. That actually
made the RF worse.
 
Thomas J. Andrews said:
I even tried running a seperate wire from the ground tab of an adapter
to a galvanized water pipe that leads out underground. That actually
made the RF worse.
Click to expand...

Try disconnecting the powersupply from *all* devices...motherboard,
harddrive, floppy, cdrom etc.
then plug just the powersupply into your AC outlet and turn the switch to
"on"

if you get RF noise now...the problem is definatly with the supply...
however...if there is no RFI ...then start connecting devices one at a time
to see which one is emitting RFI
 
philo said:
Try disconnecting the powersupply from *all* devices...motherboard,
harddrive, floppy, cdrom etc.
then plug just the powersupply into your AC outlet and turn the switch to
"on"

if you get RF noise now...the problem is definatly with the supply...
however...if there is no RFI ...then start connecting devices one at a time
to see which one is emitting RFI
Click to expand...
I did that before. The RF is there when the supply is disconnected.
 
I did that before. The RF is there when the supply is disconnected.
Click to expand...

Aha...so it has to be from the two supplies you've already tried.
If they are putting noise into the line...a line conditioner or UPS should
cure it...
but if they are directly radiating...then you will still have trouble...

You may want to try your radio in a different location
 
kony said:
Post the make/models of those you have/had please, so we
can be sure to avoid them.
Click to expand...
The one I have now, according to the sticker, is a Raidmax Technology
model PM-S400W.

Well, that explains it. My new computer has PM-S. <Grin>

I don't remember the info for the original supply, but I have reason to
think it may have been trouble before. When doing the replacement I
noticed the sealing sticker, the one that shows the case hasn't been
opened, was cut. That case had been opened sometime before I got it, for
SOME reason.
 
philo said:
<snip>

Confirm that it's grounded propery...is your outlet *really* grounded?
Click to expand...

Most countries have regulations against unwanted emissions. Get
the vendor to replace it with a satisfactory machine, or you can
sue in small claims court in many locales. Enforcing a judgement
would be up to you.

After all, that is what those regulations are for.
 
The one I have now, according to the sticker, is a Raidmax Technology
model PM-S400W.
Click to expand...

Yep, those are horrible.
I still suggest a decent name-brand with Active PFC.


Well, that explains it. My new computer has PM-S. <Grin>

I don't remember the info for the original supply, but I have reason to
think it may have been trouble before. When doing the replacement I
noticed the sealing sticker, the one that shows the case hasn't been
opened, was cut. That case had been opened sometime before I got it, for
SOME reason.
Click to expand...

A cut sticker doesn't mean too much though, I often open 'em up to see
what's inside, particularly on new/unknown generic labels.

I'd replace it with this:
http://www.newegg.com/app/ViewProductDesc.asp?description=17-103-476
 
RFI protection must be designed internally. Any plug-in solution
that is effective will be far more expensive than having bought another
and correct supply. Power supplies, as was defacto standard even 30
years ago and is required by Intel specs, must contain effective RFI
protection. Yours did not. Why? Its called forgetting to install many
essential functions so that the power supply can be sold at even greater
profits; cusomter be damned. They count on too many computer store
repairman to be bean counters; not technical literates. If your supply
is missing essential RFI protection, then it probably is also missing
other essential functions that, for example, make it not possible for a
power supply to damage other computer parts.

Note what was just posted. Many power supplies selling for less than
a retail list price of $80 are missing functions. Another often
missing function makes it possible for supply to damage disk drives and
motherboard. Still another missing function makes it possible for a
drive failure to damage power supply. RFI is but a precursor to all
kinds of other, potential, problems. That RFI is a symptom of the bean
counter mentality common in the clone computer business.

Get rid of the crappy power supplies and start buying minimally
acceptable computer components. Do not expect any plug-in solution to
fix your problem.
 
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