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Asrock Fatal1ty B450 Gaming-ITX/ac wont boot, cpu phases turn off after a few seconds. Bios?

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    Asrock Fatal1ty B450 Gaming-ITX/ac wont boot, cpu phases turn off after a few seconds. Bios?

    Hi I'm working on that asrock motherboard. It had shoted mosfet on cpu phase(changed) and 1 cap on bottom side(changed). Led driver is probably shotted too because voltage on one leg of this chip is 0.5v to 5v (its in loop rising and falling) its's RT7905 and i cant find datasheet :/ But its only led driver so mb should work without it. When i desolder it on the same leg is 5v all the time.

    If i start mb on all cpu phases is 1v1 for a few seconds only. Other voltage are present. So i tried to flash bios with the newest on official site and it doesnt help. Its not normal extension so i have to rename file to bin to flash the bios. When i tried to read ic after flashing its looks ok but it behaves as I described.

    Maybe somone has this mb and can send me bios whichone is tested on newer cpus?
    I tried on two cpus 4650g and 5600g i dont have olders. Idk what to check now. For me its looklike bad bios. I tested memory slots with tester it looks normal. I have boardview forthis mb if somone need.
  • Answer selected by Grucha98 at 01-28-2025, 06:34 AM.

    For me it looks like a hardware issue around cpu vrm. Something forces the vrm to switch off, it might have to do with over/under voltage, overcurrent or temperature monitoring network, or the cpu-vrm data communication. It can be that one cpu is working, the other not, as through the generations the cpu's can use different control methods of the vrm. So bios is probably not the issue. I would examine with a scope all the phases looking on the signals between the chokes and the mosfets and also the phase control signals on the mosfet gates, as well as check all the gate resistances (they can be the same on all gates for low side respectively high side, but must not be the same). Else I would check the values of all smd resistors, especially all low ohm resistors like shunt resistors or eg. 0R-2R2 resistors and all other smd resistors up to 100R. Else check if there are no missing / ripped off smd devices. Check whether really all other voltages are coming up with the cpu's not working, eg. for RAM. Check if vrm asserts Power Good signal, if not it indicates/confirmes problem with the cpu vrm network. Generally this kind of issue is f...g difficult to diagnose as you have only the 1 second until the vrm shuts off, so this is quite irritating and time consuming.
    Last edited by DynaxSC; 01-27-2025, 08:52 PM.

    Comment


      #2
      RT7905 http://www.raffar.com.tw/product_detail/index/15 .No datasheet just a description and different part numbers for the different packages
      All donations to badcaps are welcome, click on this link to donate. Thanks to all supporters

      Comment


        #3
        i found that too but it's only description as you said. I cant find it on aliexpress for replace. But mb should work without it

        Comment


          #4
          Originally posted by Grucha98 View Post
          i found that too but it's only description as you said. I cant find it on aliexpress for replace. But mb should work without it
          For the bios you can get it from support https://www.asrock.com/mb/amd/fatal1...ng-itxac/#BIOS ,read all the yellow text they are warning about the different CPU support. Rename the file extension from whatever number it is to .bin

          If the boardview hasn`t already been posted on the forum please post it here https://www.badcaps.net/forum/troubl...matic-requests , then post a link to it from this thread.
          All donations to badcaps are welcome, click on this link to donate. Thanks to all supporters

          Comment


            #5
            Boardview is posted on forum. I flashed bios from official site and i described it....
            Warning is for ryzens 1000/2000 etc for olders generations

            Comment


              #6
              UPDATE
              I bought used ryzen 3600. Motherboard boots and everything is normal but it's work with 3600 and gpu it can't boot with 5600g and 4650g both of these CPUs are compatible! IDK how to solve that. I updated bios via uefi to the latest stable version (not beta etc)
              Do you know how to solve that? It should boot with all 3 CPUs

              Comment


                #7
                For me it looks like a hardware issue around cpu vrm. Something forces the vrm to switch off, it might have to do with over/under voltage, overcurrent or temperature monitoring network, or the cpu-vrm data communication. It can be that one cpu is working, the other not, as through the generations the cpu's can use different control methods of the vrm. So bios is probably not the issue. I would examine with a scope all the phases looking on the signals between the chokes and the mosfets and also the phase control signals on the mosfet gates, as well as check all the gate resistances (they can be the same on all gates for low side respectively high side, but must not be the same). Else I would check the values of all smd resistors, especially all low ohm resistors like shunt resistors or eg. 0R-2R2 resistors and all other smd resistors up to 100R. Else check if there are no missing / ripped off smd devices. Check whether really all other voltages are coming up with the cpu's not working, eg. for RAM. Check if vrm asserts Power Good signal, if not it indicates/confirmes problem with the cpu vrm network. Generally this kind of issue is f...g difficult to diagnose as you have only the 1 second until the vrm shuts off, so this is quite irritating and time consuming.
                Last edited by DynaxSC; 01-27-2025, 08:52 PM.

                Comment


                  #8
                  I talked with the client and he said that's for him it's fine for now. So he will test that board. This board was in really bad conditions, idk why, many damage in diffrent spots, but without client fault (i was first to trying repair that). Thx for help guys. I dont have osciloscope to check vrm more professional

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