Motherboard Design Assumption

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  • bigbeark
    Badcaps Veteran
    • Jan 2010
    • 661
    • Canada
    #1

    Motherboard Design Assumption

    I assume that Motherboard designers locate the capacitors on motherboards close to where the particular power is required.

    So I would expect to see caps close to the Ram slots, around the CPU socket etc.

    I note that on some boards there are very few, or low powered caps near the PCI slots.

    Older boards seem to have more caps in the immediate vicinity of the PCI slots. I would assume that server boards would have more caps around the PCI slots than a desktop as more devices are likely to be installed in those slots than in a home PC with say onboard video, sound and Lan.


    The problems I have been having with my Soyo boards not loading the OS
    could be becasue I'm using a SCSI card and Drive, and perhaps the PCI slots
    which appear to use very few and notably low-powered caps on these boards just don't put enough power there to run SCSI.

    I can load the OS if I use IDE Drives, and I know my SCSI card/drive are good.

    So perhaps modern boards were never intended to have a high PCI load, and hence, are unable to provide enough juice so that my card can see the SCSI drives.

    Does this make any sense? I noted that my SOYO KT333 has no provision at all for other boot devices, for that matter, it has no boot menu within the regular bios setting and that twigged me to this thought.

    Comments please.
    Last edited by bigbeark; 01-09-2010, 07:39 PM.
    Tags: None
    • i4004
      Badcaps Legend
      • Oct 2006
      • 2029
      #2
      Re: Motherboard Design Assumption

      >and notably low-powered caps on these boards just don't put enough power there to run SCSI.

      hard drives have their own power cables, you know.

      traffic on the pci bus is mainly low-power data traffic...yes, it powers the pci-boards that are located there, but that doesn't mean you need much power there...

      also soyo kt333 is from 2002...that's not new at all.

      not loading the os via pci controller card and drive attached to it is nothing weird...
      it has to do with the way mobo's bios is setup, wether it looks for other boot devices on pci bus, or not....

        Comment

        • hardwareguy
          Badcaps Veteran
          • Jun 2006
          • 405
          • USA
          #3
          Re: Motherboard Design Assumption

          The lower number of caps is due to the lower ESR of new caps and the lower ripple output of ATX power supplies.

          With that said...the caps on the motherboard have to be *good*, and Soyo was notorious for using poor capacitors.

          i4004 is right...its a BIOS setting. Set the boot device in the BIOS to "bootable add in card" or "SCSI"

            Comment

            • kaniki
              Badcaps Veteran
              • Dec 2009
              • 514
              #4
              Re: Motherboard Design Assumption

              agreed with what was said above, but are you 100% sure that it will support booting from a scsi card.. that may be the problem.. also, maybe hook the setup up to another PC to make sure that the card has not gone bad..

                Comment

                • bigbeark
                  Badcaps Veteran
                  • Jan 2010
                  • 661
                  • Canada
                  #5
                  Re: Motherboard Design Assumption

                  My bad - I was using a cable without active termination.

                  Lots of machines seem to work fine without a terminator, but I guess if there is any marginal component at all (or maybe no nearby caps), the card doesn't see the drive.

                  Soon as I switched to a terminated card, bootup proceeded normally.

                    Comment

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