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Cheapest way to fix computer power supply RFI?

Discussion in 'General Technical Questions and Answers' started by KG9NZ, Jan 10, 2010.

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  1. KG9NZ

    KG9NZ Ham Member

    I have an old Celeron computer (2003 vintage) that I use for home automation. It is putting quite a bit of RFI on the power lines. I know the interference is coming through the power lines, because when I temporarily ran it off of a power inverter and 12V battery there was a substantial (20dB) drop in background noise in my SW receiver on the 80m band. I suspect the power supply in this computer has no RFI filtering.

    What is the cheapest and/or easiest way to solve this? I could buy an new PC power supply, but how would I know if the new power supply I bought would be any better? I did actually try a different power supply a friend had and it was almost identical as far as amount of noise. Is there some kind of filter I can plug the PC into that would be effective? Would a cheap UPS effectively isolate the computer from the line? Would wrapping the power cord around some type of ferrite core help, and if so where could I get such a core?

    Thanks,
    Frank Kienast KG9NZ
     
  2. G4LNA

    G4LNA Ham Member

    You could try buying a modern PSU for it, I dare say the PSU you borrowed from your friend was probably the same vintage, so it wasn't up to today's standards on EMC compliance. You could use a UPS but they would probably cost more than the computer PSU that would comply.
     
  3. N0SYA

    N0SYA Ham Member

    Spend some money on a good psu from a maker like OCZ, Sparkle, Enermax, or similar. And some ac power strips offer ac filtering. Also, I find it odd that the ups made for quieter rx, most ups are gigantic rfi generators.
     
  4. KG9NZ

    KG9NZ Ham Member

    Thanks for the replies.

    I actually used an automobile inverter connected to a large 12 volt gel cell battery, not a UPS, for my tests. That was significantly quieter than plugging the computer into the wall.

    The two power supplies that have high RFI:
    Original with PC: Codegen switching power supply, model 200XA1, 350W
    Borrowed: Blue Star Gold Mirror Edition 650W SATA fan ATX Power Supply

    Interference is approximately every 62kHz, but is so broad that is is practically continuous at HF.

    Anyone have any experience with either of the following two power supplies which I can get fairly inexpensively locally:
    Dynex 400W ATX Power Supply (DS400-WPS)
    BFG 450W ATX Power Supply(BFGR450WGSPSU)

    Thanks,
    Frank KG9NZ
     
  5. W9GB

    W9GB Ham Member

    Your local computer dealer can help here. Most of the local ones know JUNK from QUALITY -- However there are fraudulent companies slapping product stickers quality names on the same old junk that the Island of Taiwan continues to produce -- and local computer dealers who are clueless to RFI issues!!

    MY RECOMMENDATION? Use PC Power and Cooling (California) units --
    PRICES are the SAME as the Far East junk you are buying -- AND give you a FIVE YEAR WARRANTY !!
    Call them Monday, you will have a nice unit shipped to your door by end of the week - power supply RFI problem solved .
    Fry's Electronics was carrying this brand for awhile.
    http://www.pcpower.com/index.html

    I have purchased from this fine company when the IBM PC was NEW (circa 1982) and they produced some of the first larger wattage after-market power supplies.
    What other company would honor a long-expired warranty (1980s) for a model (AT power supply) that they now only build for custom orders?
    They did in 2002, and I only had to ship the unit back to them for rebuild and pick up the shipping charges/postage.

    I especially like their Silencer Series which reduces reduces audible noise by up to 90% (10 db)
    I have one in a larger desktop computer --- I can not hear the power supply (audible) --
    but I do hear the fans on the CPU and computer case!!
    http://www.pcpower.com/products/power_supplies/ultra-quiet/

    w9gb
     
    Last edited: Jan 12, 2010
  6. K4EEZ

    K4EEZ Ham Member

    Adding ferrite Rings, to the 115v Ac mains cable and adding smalled ferrite rings to all other wires that lead from the PSU to the main board and drives, also plug the pc in to another out let (other that the one your PSU is plugged in for the radios) will help

    of couse, if you like you can take the PC supply apart and locate the missing components

    coils L1, L2 and missing filter caps ceramic (0.03pf to 500pf @ 500v) also need to install chokes to the psu board the bigger the windings on the chokes the better filter you will make for stopping RFI

    73
     
  7. K4EEZ

    K4EEZ Ham Member

    Adding ferrite Rings, to the 115v Ac mains cable and adding smalled ferrite rings to all other wires that lead from the PSU to the main board and drives, also plug the pc in to another out let (other that the one your PSU is plugged in for the radios) will help

    of couse, if you like you can take the PC supply apart and locate the missing components

    coils L1, L2 and missing filter caps ceramic (0.03pf to 500pf @ 500v) also need to install chokes to the psu board the bigger the windings on the chokes the better filter you will make for stopping RFI

    http://etutorials.org/shared/images/tutorials/tutorial_114/fig128_01.jpg

    73 :D
     
  8. KG9NZ

    KG9NZ Ham Member

    Thanks for all the replies. I found a review for the Dynex DS400-WPS, and while they were not great, they did indicate that the supply had full RFI filtering components. I was able to get this power supply locally at a fairly cheap price. Installing it completely eliminated my RFI problem.

    Frank KG9NZ
     
  9. AG3Y

    AG3Y Ham Member

    Glad you fixed your problem. But I would like to add that there are several filtered sockets that will fit in the same place as the original unfiltered one, that will drop the buzz coming from inside the power supply down to almost insignificant levels. They incorporate coils and capacitors in a Pi filter arrangement, and are only a few inches long, while dropping into the same hole provided on the case for the original socket. You may have to move some components around on the circuit board to allow for some additional depth, but that will usually not be that much of a problem.

    Look at Mouser, or some other component catalogs and you should be able to find them.

    Again, this will not help in your case, but others might be able to benefit in the future!

    73, Jim
     
  10. KB3TYW

    KB3TYW Ham Member

    Supply RFI

    W9GB is correct. There are many JUNK builders of PSU's out there.:(
    A site I found a few years ago, badcaps.com is almost as good as this one as far as the technical expertise is concerned.:eek: They taught me a lot about caps. The site is mostly for motherboard repair but they discuss almost anything espically about bad caps, what manufs. make good ones and what to do about fixing audio,computer,video equipment that has failed. Good troubleshooting site also.:rolleyes: So what does this have to do with RFI. Those who go to the site have vast experience in, among other things, PSU's. Just go there and ask or read their forum section on PSU's.
    BTW, if you whant to experiment then the previous post covered all the bases that I could think of. A Corcom line filter and some ferrite material might just do the job. But, after all that's said and done do you want to fix a supply with bad design and parts?
    73
    KB3TKW

     
  11. KA5S

    KA5S Subscriber

    4 of 6 computers exceeded limit

    A recent posting on the IEEE emc-pstc list noted that of 6 computers an independent test lab checked for conducted emissions, FOUR failed to meet the FCC Part 15 reqiuirements -- and when he opened the 'hottest" one he found the on-board EMC filter components provided for -- but absent or replaced with jumpers.

    I have permission to quote from his message:

    I should note that turning in violators wasn't his objective; he was LOOKING for a quiet computer to test client equipment with.

    I'd also like to suggest that just because you can hear a power supply is no assurance it is in violation of FCC requirements. If you own it, you're supposed to turn it off! A flood of complaints where only a few turn out to be well founded would make the FCC less willing to entertain even well documented ones.


    Cortland
    KA5S
     
  12. N5YPJ

    N5YPJ QRZ Moderator

    I had an eMachine PC for several years supposedly one of the cheapest quality PCs onthe market and not a bit of RFI. The PS died and I replaced it with a Universal PS and had RFI all over the place. I opened up both PS and took a toroid off of the dead one and put it on the good one's AC input that quietened things down a bit. Eventually though I still had more noise than I liked so I bought a case with a PC because the old case had no room for a more modern PS and things got nice and quiet again. Check if your case has space for one of the modern supplies and if so change it out, if not and the PC is worth it to you then get a case / PS combo.
     
  13. W9GB

    W9GB Ham Member

    There are a LARGE number of PC power supply sizes .. even RFI quiet ones for the eMachine cases.

    The ATX Power Supply Design standard is written and published by Intel.
    The original ATX power supply specification remained mostly unrevised from 1995 until 2000.
    http://en.wikipedia.org/wiki/ATX#ATX_power_supply_revisions

    This should be educational for those that are converting these supplies for amateur radio usage -- specifically read the ATX12V 2.0 (February 2003) changes.
    Although the ATX power supply specifications are mostly vertically compatible in both ways (both electrically and physically), there are potential issues with mixing old motherboards/systems with new PSUs, and vice versa. The main issues to consider are the following:

    * The power distribution biases across 3.3 V, 5 V, and 12 V rails are very different between older and newer ATX PSU designs, as well as between older and newer PC system designs.
    * Older PSUs may not have connectors which are required for newer PC systems to properly operate.
    * Newer systems generally require larger power supplies than older systems.

    For example, Older Dell computers, particularly those from the Pentium II and III times, are notable for using proprietary power wiring on their power supplies and motherboards. While the motherboard connectors appear to be standard ATX, and will actually fit a standard power supply, they are not compatible. Not only have wires been switched from one location to another, but the number of wires for a given voltage has been changed. Thus, the pins cannot simply be rearranged.
    PC Power & Cooling makes specific power supply replacements ONLY for usage in these Dell computers.

    w9gb
     
    Last edited: Jan 13, 2010
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