Strange resistance readings on Radeon RX6800 VRM

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  • dicky96
    Sun Seeker
    • Mar 2017
    • 1825
    • Spain
    #1

    Strange resistance readings on Radeon RX6800 VRM

    Hi guys
    I can't quite get my head around the resistance readings on this GPU

    On phase of Vcore VRM reads higher resistance than the others

    This 3 mins video shows exactly what I mean
    https://www.youtube.com/watch?v=NZR4otU77VE

    I can't think any way this could happen unelss one phase is not directly connected to the others, but is conetced via a low value resistance

    Can someone unconfuse me please

    Cheers
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    • momaka
      master hoarder
      • May 2008
      • 12164
      • Bulgaria
      #2
      Re: Strange resistance readings on Radeon RX6800 VRM

      TBH, I'm not too familiar with these newer gen GPUs, so perhaps it is possible that this one phase is not connected to the others. Have you traced the MOSFETs for that phase to see if they are exactly connected like the MOSFETs on the other phases (and to the same controller)? I think that might be the first clue in telling if that's part of the GPU VRM or some secondary GPU VRM. I do agree that it's strange that only this one coil reads higher resistance, though. I'd expect to see at least another phase in parallel with it, if it was to be some secondary GPU VRM rail. On the other hand, if all of these phases were to be connected together, then the only way that higher resistance would be there is if the copper trace from the coil to the GPU chip has burned and gone high resistance... which I think would be highly unlikely.

        Comment

        • dicky96
          Sun Seeker
          • Mar 2017
          • 1825
          • Spain
          #3
          Re: Strange resistance readings on Radeon RX6800 VRM

          Hi Momaka
          Thanks. It shouldn't be too difficult to see if this phase goes to the same controller as the other phases, for example if there is an 8 phase VRM controller

          But I couldn't find a datasheet for the coil driver IC either so that does not exactly help

          Because this one phase still has a very low resistance to ground it also seems odd to me that it would be a singleton as you mentioned.

          I could just try powering the card up and measure the voltage on this and other inductors on the VRM - but I really would like to understand what I am looking at first.
          Last edited by dicky96; 09-12-2021, 10:55 AM.
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            Comment

            • dicky96
              Sun Seeker
              • Mar 2017
              • 1825
              • Spain
              #4
              Re: Strange resistance readings on Radeon RX6800 VRM

              OK I pretty much got to the bottom of this - at least I have a plausible theory for the odd resistance readings on the VRM

              The fault on this card appears to be elsewhere

              It's easier to watch than for me to explain in detail what I worked out

              https://www.youtube.com/watch?v=ooefNfC8Lxg

              Rich
              Follow me on YouTube
              ------------------
              Learn Electronics Repair
              https://www.youtube.com/channel/UCFX...R8UZ2vg/videos

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