NF325-A7 Biostar AMD 754 Processor Power On Problem

Discussion in 'PC Hardware' started by David Sontag, Oct 28, 2006.

  1. David Sontag

    David Sontag Guest

    I have a power on problem I do not understand. This board has a
    JATXPWR ... the "extra" 4 pin power connector... When I first powered
    up this build it would not post .. no beep nothing. After
    trouble shooting for some sort of short ... which I did not find ,,, I
    unpluged this "extre" 4 pin +12v connector. Now the board posts.

    I do not have it hooked up to a monitor yet so I do not know if it
    really works, but I am assuming since the connector is there the
    system will not work without it?

    The connector is keyed with two rounded female pins so I think I have
    connected it right.

    Now my thinking is the power supply is bad... it is an Ultra ... given
    the reviews it is the next thing I will change ... unless someone has
    a better idea.


    David Sontag, Oct 28, 2006
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  2. David Sontag

    Paul Guest

    I can propose a theory to explain it, but you'll have to prove
    or disprove it yourself. (bigger picture)

    The 2x2 connector powers the processor. It goes to the Vcore converter,
    which is next to the connectors.

    Most motherboard makers, separate the 2x2 12V rail, from the 12V pin on
    the main connector. On most motherboards, if you do not connect the 2x2
    connector, the motherboard will not POST.

    I believe I have heard of Biostar boards before, POSTing and booting
    with the 2x2 disconnected. This means that the 2x2 connector and the
    main connector, are both connected to +12V. (NOT a good idea.)

    This is how most motherboards are wired:

    2x2 ATX12V ---- +12V ---+-----------> Vcore (processor power only)
    showing ---- +12V ---+
    all four ---- GND
    pins ---- GND

    20 pin ---- +12V ---------------> fans, video slot, etc.
    (pin 10)

    This could be how your Biostar is wired:

    2x2 ATX12V ---- +12V ---+----+------> Vcore (processor power only)
    ---- +12V ---+ |
    ---- GND |
    ---- GND |
    20 pin ---- +12V --------+------> fans, video slot, etc.
    (pin 10)

    With the theoretical diagram above, if only the 20 pin is plugged
    in, the Vcore for the processor gets power, and the board boots.

    Now, the fun part. The part Biostar forgot. There are a number of
    new power supplies on the market, with dual 12V power rails.
    They are called 12V1 and 12V2. Now, many of the supplies internally,
    are actually powering both 12V1 and 12V2 from a common 12V source.
    A limited number of supplies, may have completely separate 12V
    outputs. I'm going to show the "pesky" case here - a supply with
    independent 12V1 and 12V2 connected to the Biostar board:

    12V2 ---- +12V ---+----+------> Vcore (processor power only)
    ---- +12V ---+ |
    ---- GND |
    ---- GND |
    12V1 ---- +12V --------+------> fans, video slot, etc.

    Notice in this case, that with the proposed Biostar wiring, that
    12V1 and 12V2 are shorted together. This is Not Nice if the
    supply has independent outputs. The supply may detect this
    connection, and shut off. You may see the fan "twitch" when
    you push the power button, and that is all. You may have to
    shut off the supply at the back, before you can switch on
    at the back again, push the power button, and get another
    "twitch" out of it.

    If you look carefully at the Biostar PCB layout, the 2x2 connector
    is very close to the 20 pin connector. Notice how the 2x2
    connector is pretty damn close to pin 10. It would be a
    cinch for them to wire the two outputs together.

    Your motherboard would not have had a problem with an older
    pre-ATX 2.0 type power supply. It is more modern and readily
    available power supplies that _could_ have a problem with
    the above proposed wiring. You could have got lucky, and
    used an ATX 2.0+ supply, and been unaware of what was
    happening (if the supply internally had joined 12V1 and
    12V2 together to the same rail).

    Given that you keep this computer as it is currently configured
    (i.e. only the main power connected, and the 2x2 disconnected),
    the question would be, is it safe ? If you had an 89W processor,
    and a 6600GT video card, you could be drawing 13 amps through
    pin 10 on the main connector. That condition would exist, if
    you ran 3DMark on your new computer. (Don't run it yet!)
    If the hardware is sitting idle in the desktop, the power
    consumption is a lot lower, low enough in fact so that your
    may not have burned the connector pin yet. Pin 10 on the
    connector (or any pin on the main 20 pin connector) is
    rated for 6 amps, and if you ran 3DMark right now, the pin
    could start to overheat, at 13 amps.

    I cannot give a good recipe for getting out of this mess.

    If you are well equipped hardware wise, and have a multimeter,
    you could probe pin 10 on the motherboard when the power supply
    is disconnected. See if there is zero ohms (a short) between
    the two 12V pins on the 2x2 connector, and pin 10 on the main
    connector. That would confirm the theory, that Biostar connected
    them together (which they should not have done).

    You could rewire the harness from the Ultra, to suit the Biostar.
    It would require cutting the connection to pin 10, and splicing
    12V power from one of the two pins on the 2x2 connector. That
    way, the entire motherboard would be running from 12V2 on the
    Ultra. That is OK, assuming the current rating of the
    Ultra supply is high enough to power the load (like 13 amps in
    my quoted example). You can look at and look up
    the power rating of your processor. And if you state what video
    card you've got, I can look up on Xbitlabs, how much +12V it uses.

    A second alternative, is to find an older power supply. One that
    does not list "12V1 and 12V2", but just talks about a single 12V
    rating. Those older supplies join the 2x2 12V wires to the pin 10
    wire of the main connector. One of those older supplies would
    be compatible with what Biostar has done. For example, this one
    looks like an ATX 1.3 type supply, with common 12V output rail.
    The customer reviews note that the 24 pin connector, comes apart
    into a 20pin plus a 4 pin section, so you can convert it to
    20 pin format, by just sliding off the extra 4 pins. (To
    determine whether this has enough power, list all your hardware
    and I can do an estimate for you. Or look up one of my many
    other efforts at power estimation, to see the method to use.)

    ENERMAX EG365P-VE FMA 1.3 ATX 350W Power Supply 12V @ 26A $55

    Notice that if you sum voltage times current for all the rails,
    the total would be more than 350W. The idea is, power supplies
    have high ratings, assuming not all rails are heavily loaded
    at the same time. Most of your system power comes from +12V,
    and less from the others. Maybe your total system power would
    not be over 200W, which would fit within the 350W total

    (12*26 = 312 watts, and the other rails, the +3.3V and +5V,
    could only provide 38 watts, if the 12V goes to the max.
    They would use the "left over" capacity from the 350W total.
    But your system might be drawing at worst, 16 amps from +12V,
    leaving room for +3.3V and +5V. So while this supply may sound
    weak to you, it may power your system just fine.)

    If you aren't comfortable with the low total wattage rating,
    there are larger ones. This one is 550W, and has a 20+4
    main power connector (detaches):

    Paul, Oct 28, 2006
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  3. David Sontag

    David Sontag Guest

    Hi Paul,

    First I want to thank you for taking the time to type this all in and
    shed light on this kind of power supply issue.

    You were right the !2v-1 and the 12v-2 are tied together on this
    motherboard. The ultra 450w supply has two separate rails ....
    plugging them in to the board ties them together and thus no post as
    the power protection prevents the power supply from turning on.

    When I replace the Ultra Supply with a cheap A-Power 450 w ...
    with one +12 rail and the 4 "extra" pins it works just fine
    (considering I have not damaged the motherboard--- which I will know a
    little later today).

    All this said .... the A-Power only has 15A of +12v .... which may not
    be enough or as per your discussion it may be fine. This is not a
    gaming machine. Just a Radeon 9250 and some extra USB cards and a

    So ... now I have to find a supply that sources twice that ~ 30A on a
    signal rail like the ENERMAX EG365P-VE FMA 1.3 ATX 350W Power Supply.

    Thanks Again!

    David Sontag, Oct 28, 2006
  4. David Sontag

    Paul Guest

    The 9250 probably does not draw a lot of current. Still, I don't
    expect you'd have a problem with a 550W supply, in any case.

    Paul, Oct 28, 2006
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