FP6321A drop-in replacement

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  • SIDMX
    Senior Member
    • Nov 2010
    • 165
    • Mexico

    #1

    FP6321A drop-in replacement

    This is the board that was blown by the FSP F350-A, it's a Biostar 945GC-M4, finally get the time to give it a try at fixing it but with not so much hope, since this wasn't a badcaps issue I decided to post it here in case that someone find it useful.

    The board didn't power on, fan does not spin at all however 3VSB was present, found 3 mosfet (Nikos P0903BDG) and a SOP-8 IC (FP6321A) shorted, one of the mosfets was in cpu vrm and the other two in a DC-DC converter along with the FP6321A which is a 300Khz fixed-frequency synchronous buck controller, all shorted mosfets were replaced but couldn't find any FP6321A in my junk box however I found in some russian forums that APW7120, RT9214 and a few others could be suitable replacements, datasheets seems to back that, anyway I scrapped both (APW7210 and RT9214) from dead boards and tried the APW7120 first but that was a no-joy, maybe I just killed the chip during the scrapping because I don't own any SMD rework tool so soldering/desoldering was made with my soldering iron and the burnt marks in the pictures can confirm that.
    Next I replaced the APW7120 with the RT9214 and this time the board finally powered on, quick testing with a Prescott Celeron 2.26GHz and some DDR2 confirmed that the board was indeed alive and posting however my real surpise was the fact that this board DOES SUPPORT MOBILE P4's! I got 3 of them ranging from 2.8 to 3.2GHz like three years ago from old VAIO PCG-KxxF series laptops and none of the 478 boards that I have put my hands on ever posted with any of them, not even this one and then this cheapo board just works prefectly with any of them, although mosfets from CPU VRM gets somewhat hot at 78°C but that is thanks to the Mobile Pentium 4 538 that was used in the test.
    Back to topic the board passed 12hrs of Memtest and AIDA stability test (FPU stress), full install of Win 7 SP1 + some software and around 4hrs of normal use, email, tube, mp3 play and office suite so I can confirm that RT9214 is a possible drop-in replacement for FP6321A.
    Attached Files
    Last edited by SIDMX; 12-05-2013, 05:07 AM.
  • momaka
    master hoarder
    • May 2008
    • 12170
    • Bulgaria

    #2
    Re: FP6321A drop-in replacement

    Nice save!

    Yeah, this is the only reason why I keep old junk motherboards and hardware - MOSFETs and controllers (and occasionally some other SMD parts too). I sort-of fixed a P4IBMs last week that needed a P-channel SOT-23 MOSFET. It's amazing how something so simple can be actually so rare. None of my junk boards had one except for one ASUS board (and I DO have a lot of junk boards and electronics).

    Comment

    • SIDMX
      Senior Member
      • Nov 2010
      • 165
      • Mexico

      #3
      Re: FP6321A drop-in replacement

      Thanks, I too keep junk boards for the same reason, must have like 50 or something close to that number, sometimes the real problem for me is to actually ID the part (sot-23 and smaller) specially if the part is not silk-screened in the PCB.

      About your P4IBM why the "sort-of fixed"?

      Comment

      • momaka
        master hoarder
        • May 2008
        • 12170
        • Bulgaria

        #4
        Re: FP6321A drop-in replacement

        Yeah, SOT-23 component's that lack silk-screen on the board are extra hard to find because you don't know if the device is supposed to be a diode, a MOSFET, a BJT, or a 431 shunt. When it has a designator on the board, at least you have an idea what to look for.

        As for the P4IBMS, the board worked "okay" originally (more or less), but with the shorted SOT-23 P-channel FET, one of the linear regulators on the board was overheating badly, and the board wasn't very stable because of this. Replacing the FET fixed this. However, there is still this bug that, when the PC is plugged in the wall for the first time after power loss, that regulator still overheats. If I turn ON the motherboard, it stops overheating. If I then turn the motherboard OFF, it never overheats unless PSU looses power. So my fix for now is to enable the "Turn ON after power loss" option in BIOS.

        Comment

        • SIDMX
          Senior Member
          • Nov 2010
          • 165
          • Mexico

          #5
          Re: FP6321A drop-in replacement

          Very weird behavior , but it should be something non critical if the board works, what is supposed to feed that regulator's output?

          Comment

          • azou
            Member
            • Jun 2016
            • 15
            • alger

            #6
            Originally posted by SIDMX
            This is the board that was blown by the FSP F350-A, it's a Biostar 945GC-M4, finally get the time to give it a try at fixing it but with not so much hope, since this wasn't a badcaps issue I decided to post it here in case that someone find it useful.

            The board didn't power on, fan does not spin at all however 3VSB was present, found 3 mosfet (Nikos P0903BDG) and a SOP-8 IC (FP6321A) shorted, one of the mosfets was in cpu vrm and the other two in a DC-DC converter along with the FP6321A which is a 300Khz fixed-frequency synchronous buck controller, all shorted mosfets were replaced but couldn't find any FP6321A in my junk box however I found in some russian forums that APW7120, RT9214 and a few others could be suitable replacements, datasheets seems to back that, anyway I scrapped both (APW7210 and RT9214) from dead boards and tried the APW7120 first but that was a no-joy, maybe I just killed the chip during the scrapping because I don't own any SMD rework tool so soldering/desoldering was made with my soldering iron and the burnt marks in the pictures can confirm that.
            Next I replaced the APW7120 with the RT9214 and this time the board finally powered on, quick testing with a Prescott Celeron 2.26GHz and some DDR2 confirmed that the board was indeed alive and posting however my real surpise was the fact that this board DOES SUPPORT MOBILE P4's! I got 3 of them ranging from 2.8 to 3.2GHz like three years ago from old VAIO PCG-KxxF series laptops and none of the 478 boards that I have put my hands on ever posted with any of them, not even this one and then this cheapo board just works prefectly with any of them, although mosfets from CPU VRM gets somewhat hot at 78°C but that is thanks to the Mobile Pentium 4 538 that was used in the test.
            Back to topic the board passed 12hrs of Memtest and AIDA stability test (FPU stress), full install of Win 7 SP1 + some software and around 4hrs of normal use, email, tube, mp3 play and office suite so I can confirm that RT9214 is a possible drop-in replacement for FP6321A.
            Thank you.

            Comment

            • truclacicr
              Badcaps Veteran
              • Apr 2019
              • 296
              • australia

              #7
              https://www.richtek.com/assets/produ.../DS9214-15.pdf (RT9214)

              https://cwispy.com/wp-content/upload.../10/fp6321.pdf (FP6321)

              Comment

              • azou
                Member
                • Jun 2016
                • 15
                • alger

                #8
                finally i replaced FP6321A with APW7120 and worked for me .Thank you .

                Comment

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