Asus Probe voltages fluctuate

Discussion in 'Asus' started by jimbo, Apr 4, 2005.

  1. jimbo

    jimbo Guest

    On my P4C800E-Deluxe, Asus probe shows the +3.3V line at 3.04V and every few
    minutes it drops to 2.96V, where it gives off some beeps. Then back up to
    3.04V. then 3.008.
    The 12V graph isn't straight over time but bumpy with dips. Vcore graph line
    & +5V line are solid.
    What does the +3.3V provide power for? I'am having big problems with this
    board, like no drives detected in bios on the southbridge, including SATA.
    I've got a new 500watt PSU coming in this week so I can test it out.

    Jimbo
     
    jimbo, Apr 4, 2005
    #1
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  2. jimbo

    Brad Clarke Guest

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  3. jimbo

    Paul Guest

    Quite true. I noticed the difference between the monitor chip
    readings and my voltmeter. The voltmeter readings looked
    to be very close to nominal and quite steady, while the Probe
    readings were wandering around.

    I still wouldn't ignore the 3.3V warning however. That could
    be indicating that your ATX 20 pin power connector is loose.
    Turn off and unplug the computer. Unplug the 20 pin connector
    and examine it carefully. Look for melted plastic or discolored
    metal on the connector pins. These could be signs of thermal
    damage.

    The original cause could be something as simple as
    the connector not being fully seated, which causes the
    resistance between the connector and motherboard to be
    higher than normal. The pins get hot, and the metal
    oxidizes. The plastic melts next to the pin, if they
    get hot enough.

    There was one model of Asus motherboard, where users noticed
    the connectors fit sloppy on all the boards, implying a
    quality control problem at the factory making the connectors.
    I have not heard of that problem being repeated, and presumably
    Asus no longer buys those connectors.

    Once the surface finish of the pins is damaged, the
    connection will never be the same again. Even if you
    somehow had a technology to clean the pins, they would
    still degrade further over time. The original finish of
    the pins is very important, as the metallurgy (layers of
    metal plating) are selected for long life, and if they
    are disturbed, all bets are off.

    If the finish of the connectors is damaged, the only way to
    guarantee a fix, is replace the connectors on both ends.
    That would mean soldering a new connector on the motherboard,
    and installing a new mating connector on the power supply.

    The other possibility, is the connectors are good, but the
    power supply is weak. You will know soon enough, when you
    get your 500W supply.

    I can't state positively, what devices feed off the 3.3V. I
    can tell you, that the board does have a number of linear
    regulators (designed low dropout style, to minimize the
    heat generated), constructed with MOSFETs and quad op amps.
    It is possible the 3.3V is used to power the RAM (via 3.3
    to 2.5V linear regulator), and then the 2.5V is further
    dropped to voltages like 1.8V or 1.5V, for other chip uses.

    Actually, I have some measurement data. DDR400 2-2-2-6 memory.
    P4C800E-Deluxe. 2.8Ghz Northwood.

    1 stick DRAM single channel - sitting idle in BIOS = 3.3V @ 8.1A
    2 sticks DRAM single channel - sitting idle in BIOS = 3.3V @ 9.0A
    2 sticks DRAM single channel - memtest86 = 3.3V @~10.5A
    2 sticks DRAM dual channel - memtest86 = 3.3V @~11.6A
    4 sticks DRAM dual channel - memtest86 (PAT on) = 3.3V @~14.4A
    ~ means approximate, as memtest current jumps around during
    the reading and writing of blocks of data.

    The 14.4 amps is spread over three connector pins. The pins
    are rated for 6 amps each or 18 amps total. There would only
    be a problem, if the currents were not shared fairly by the
    three connector pins. Which has happened on a Tyan motherboard...

    Paul
     
    Paul, Apr 5, 2005
    #3
  4. jimbo

    Larry Gagnon Guest

    Jimbo: never trust software voltage and temperature readings. They are
    notoriously unreliable. All you have to do is go back in history through
    this newsgroup and see the variation people report between various
    software monitor programs. The only true reading of voltages and voltage
    variations are made with a digital VOM at the motherboard power
    supply connector.

    Larry Gagnon, A+ certified tech.
     
    Larry Gagnon, Apr 5, 2005
    #4
  5. From: "jimbo" <>

    | On my P4C800E-Deluxe, Asus probe shows the +3.3V line at 3.04V and every few
    | minutes it drops to 2.96V, where it gives off some beeps. Then back up to
    | 3.04V. then 3.008.
    | The 12V graph isn't straight over time but bumpy with dips. Vcore graph line
    | & +5V line are solid.
    | What does the +3.3V provide power for? I'am having big problems with this
    | board, like no drives detected in bios on the southbridge, including SATA.
    | I've got a new 500watt PSU coming in this week so I can test it out.
    |
    | Jimbo
    |

    If it is supposed to be 3.3v anf you get a nominal 3v. Then that is a 10% less than the
    actual required volatge. If the volatage is 3.00v and drops to 2.96 and goes up to 3.04v
    That +/- 1.3% deviation. That is good for a regulated DC voltage and could actually be a
    AC ripple component. The real question is what are the voltages in both loaded and unloded
    conditions. If it is supposed to provide 3.3v and unloded it is a steady 3.3v but under
    load it drops to 3.0v with a +/- 1.3 varaiation, that may be out of spec.

    The reason a voltmeter and the chip might show a differences would be due to the internal
    impedance of the two different devices. The higher the impedance, the higher the accuracy
    of the voltage reading device. The lower the impendance the less accurate it will be and
    the ripple component may not show.
     
    David H. Lipman, Apr 5, 2005
    #5
  6. jimbo

    Peacekeeper Guest

    Jimbo out of interest what is the wattage and brand of your current supply?
    Peace
     
    Peacekeeper, Apr 6, 2005
    #6
  7. jimbo

    jimbo Guest

    It's a Leadman Powmax Ultra 500Watt.
    My new psu is due to arrive today.

    Jimbo
     
    jimbo, Apr 6, 2005
    #7
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