antec 550w w/ LOW +5v rail

Discussion in 'Asus' started by OverKlocker, Jun 9, 2004.

  1. OverKlocker

    OverKlocker Guest

    i just noticed my +5v rail is running between 4.38 to 4.5 volts. not
    sure how long it has been doing this, but my system has been a little
    erratic over the last few weeks. normally my rig is rock solid. i
    dropped my fsb from 200 back to 166, lowered my voltages back to
    normal, disconnected all of my drives, and it is still on the low
    side. i've had my antec true power 550w for about 2 years (maybe a
    little longer). i thought i had a bad sata hdd or dvd burner, but
    nogo. also my 3.3 is about 3.28, and my 12 is 11.37. my system and my
    22"nec monitor are plugged into an APC Back-UPS Pro 1000. does this
    sound like an RMA issue? seems like it to me. thanks in advance.

    System Specs:
    Asus A7N8X Del 2.0 (1007 Uber bios)
    2500+ @3200+ (2.2 Ghz) 200 fsb
    Thermalright SLK-800(A) (with AS3 and 80mm Denki fan)
    1Gb Corsair pc3200 CL2 (2 sticks, with platnium heat spreaders)
    Radeon 9700 Pro retail w/Aluminum ram sinks
    22in NEC MultiSync FE1250
    160 gig Maxtor SATA 7200rpm 8mb (XP Home SP1)
    120 gig Maxtor PATA 7200rpm 8mb (data/backups)
    Optorite dd0203 DVD burner
    Artec 52x24x52 cdrw
    Lian-Li pc10 (with window and light mod)
    550W Antec True Power PSU
    Phoebe v.92 pci modem
    onboard sound
    onboard nic
    OverKlocker, Jun 9, 2004
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  2. Il Wed, 09 Jun 2004 04:30:37 -0500, OverKlocker ha scritto:
    Yes, that is the problem of your system instability.

    Definitely broken PSU, I think. Or do u maybe have electrical problem in
    the house?
    _P_e_ar_lALegend, Jun 9, 2004
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  3. OverKlocker

    Nero Guest

    Mine is at 4.84V and I have no problems.
    Is that reading taken accross the - and + 5Volt rail or just the reading
    your software tells you?
    The only way to take voltage readings is by connecting a volt/test meter
    directly to the leads/connectors on the PSU and not any other way.
    What you see is after the MB regulates the voltage and not off the PSU.
    Nero, Jun 9, 2004
  4. OverKlocker

    Nero Guest

    You will only get a proper reading by connecting a test/volt meter across
    the - and + 5 volt rail on the psu.
    You cannot get an accurate reading by software or by what it says anywhere
    Mine is 4.84V and never any problems or slowing down.
    The reading you see via windows or software is after the onboard regulation.
    Nero, Jun 9, 2004
  5. Il Wed, 09 Jun 2004 13:07:41 +0100, Nero ha scritto:
    Well, hardware monitor, especially the one implemented in the bios, is not
    perfect, but quietly accurated. If it say 4,3 and u have problem, it's
    becouse it really is 4,3.
    4.84 is acceptable. 4.5 or less it's not.

    the +5V is the most important reading for the stability and the
    performance of the system: it handle the cpu power and have to be
    perfectly stable and power enough.

    My Enermax is actually 5.01 and system run great.

    I had, in the past, low cost power supply with 4.7/4.8 reading and system
    never been so stable like it's now.

    I can say it's much more better to have a HIGH quality 250 PSU (I do have
    an old 250 AOpen, rock steady at 5,03 running a totally stable 333/2400+
    on an Abit board).
    _P_e_ar_lALegend, Jun 9, 2004
  6. OverKlocker

    Steve Birch Guest

    My 550W enermax gave some very strange voltages (including low outputs) when
    the +12V supply was not actually loaded hard enough.
    I noticed that when I added more disk drives, the voltages became perfect.
    If you read the specifications carefully, most power supplies have a minimum
    load requirement on some of the outputs.
    Just a thought....

    - Steve
    Steve Birch, Jun 9, 2004
  7. OverKlocker

    DaveW Guest

    Your power supply is failing.
    DaveW, Jun 10, 2004
  8. OverKlocker

    OverKlocker Guest

    power in the house is fine, plus my APC Back-UPS Pro 1000 should
    condition the power if it was off slightly. more than likely, i'm will
    be calling antec...LOL
    OverKlocker, Jun 10, 2004
  9. OverKlocker

    Nero Guest

    No it's not................
    like I said that reading is after onboard(MB)regulation.
    I connected mine to a different MB and got a different reading.
    Unload the 5v rail and then see.
    Nero, Jun 10, 2004
  10. OverKlocker

    Paul Guest

    What you are seeing, is not onboard regulation. The +5V from
    the PSU is connected directly to the monitor chip. It is not
    modified before it gets to that chip.

    Onboard regulation is used to create new voltages, that don't
    come from the power supply. Or to create voltages that can be
    programmed by the BIOS or in response to a hardware signal on
    the board. For example, +3.3V comes from the power supply,
    but won't be used directly to power AGP I/O. That comes from
    a separate regulated supply, but that supply needs the ability
    to generate either 3.3V or 1.5V, depending on the TYPEDET# signal
    on the AGP connector. So, that is an example of where a
    programmable feature is needed, so the PSU power cannot be
    used directly.

    The reason you see the PSU voltages change, as you move from
    motherboard to motherboard, has to do with the tolerances of
    the voltage measurement done by the monitor chip. The monitor
    chip on the motherboard is uncalibrated. If motherboard
    manufacturers cared, they could feed precise voltages to the
    circuit during manufacture, and work out compensating gain
    and offset values, to improve the accuracy of the readings.
    They don't do this, because there is no where to store the
    info (a BIOS flash would wipe it out).

    For example, the Winbond W83627THF has an eight bit ADC for
    voltage measurement, and a full scale value of 4.096V on
    input. The minimum step size is 0.016V. The converter is
    successive approximation type, so uses a DAC to make voltages
    and does a binary search at 22KHz to try and match the
    voltage it is measuring. The DAC is powered by an internal
    reference called Vref, and that will have an accuracy, as to
    how well it keeps its value. The DAC will use switched resistors,
    and they have to be well matched, for the voltages it creates
    to be smooth with respect to the eight bit number it is working
    with. A typical chip Vref is only good to maybe 2%, or lower
    tolerances are possible if devices are sorted according to
    how well they make a reference voltage. Like all fine quality
    datasheets, Winbond doesn't state how well the circuit works.

    So, you have maybe 2.5% accuracy to start with. For voltages
    outside the Winbond chip, requiring a voltage divider, to
    make the voltage fit within the 4.096V measurement range,
    two 1% resistors will be used. Their tolerances add, so now
    the accuracy of the measurement is around 4.5% worst case.

    Let us say you are interested in the voltage of +5V. On one
    motherboard, the reading could be 4.5% low, and read 4.775V
    On another motherboard, the reading could be 4.5% high, and
    read 5.225V. Even though it is the same voltage from the
    same PSU.

    If you buy a multimeter, the multimeter is calibrated at the
    factory, and that allows more accurate readings than the
    motherboard circuit. The cheap meters I own are good for
    2% plus 1 LSB or so. Multimeters have at least the equivalent
    of a 12 bit ADC, which has a much better step size than the
    8 bit SAR ADC of the Winbond chip. That is why measuring
    the power supply with a meter is so important, as the
    meter can read very accurately (the more money you have to
    spend, the better they get).

    "Homey", the guy who repairs motherboards, measures PSUs and
    finds them to be doing much better than the motherboard
    monitor would have you believe. I think he owns a good meter.

    So, find a multimeter, and measure the supply while it is
    under load. It is easy to get to the +5 and +12 voltages,
    by using a drive power connector. The +3.3V can be read
    from a 6 pin AUX power connector. The -5V and -12V don't
    matter, and the reading from the monitor chip is good
    enough, to at least determine they aren't grossly

    Also, try unplugging the ATX20 pin connector, and then
    replugging it (with PSU unplugged). Sometimes the contacts
    aren't making good contact, and reseating the connector
    will help for a while.

    Paul, Jun 10, 2004
  11. OverKlocker

    john Guest

    Yeah, and don't forget to put in a fresh battery.

    I hooked up a 9$ meter and read 16 volts on my 12 volt line.
    Blinked twice, figured it out, and haven't worried about it since.

    Gonna have to get a new battery in there someday ;)
    john, Jun 10, 2004
  12. OverKlocker

    OverKlocker Guest

    lots of good info here thanks, atx connector was already reseated,
    also bypassed the APC unit (just in case), removed my modem, my backup
    120gig hdd, and my dvd burner. so... running 1 hdd, 1 cd/rw, 9700pro,
    i'm still getting 4.48-4.57 on my +5v rail.
    OverKlocker, Jun 10, 2004
  13. lots of good info here thanks, atx connector was already reseated,
    Ask a friend for a new PSU to try or buy a new one: a system can't never
    run stable with that low +5.

    U need to check whats goin on.
    _P_e_ar_lALegend, Jun 11, 2004
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