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inno3D GTX780 no picture, not recognized

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    inno3D GTX780 no picture, not recognized

    Hi guys,

    I have a inno3D GTX780 on my bench which has a defective GPU VRM Mosfet Sic780. I removed this and wanted to test the card. The card doesn't give any picture and is not recognized by windows. So I measured the main voltages and there I saw the culprit. Some voltages are missing as you can see in the attached images. The two PWM-Controllers do not have an enable voltage. Now my question. Does anybody know where the enable voltages are generated?

    Best regards
    Attached Files

    #2
    Re: inno3D GTX780 no picture, not recognized

    Yes
    One of the three GTX780s I looked at had no EN signal like yours, The EN voltage is derived from the 3.3V or 12V on the PCI-e connector. On mine, once I fixed that by fitting a patch wire because I could not find where the faulty track or resistor was, I got the card to boot but had artifacts on screen.

    Sorry it was quite some time ago and I do not remember the exact details now, but read this thread through and you will probably find the info to help you

    https://www.badcaps.net/forum/showthread.php?t=83970

    Rich
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      #3
      Re: inno3D GTX780 no picture, not recognized

      Thanks for your answer. The linked thread I do know. So I will try to find out the faulty component. I think this will be difficult because till now I can't trace back where the signal comes from or should come from. I will test again and keep you informed.

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        #4
        Re: inno3D GTX780 no picture, not recognized

        In my case it was a broken PCB trace or via I think.

        You have to have the power coming in from the PCI 12V/3.3V to the GPU before anything of the other VRMs will start up. I think the 3.3V acts as a standby supply to the GPU BGA itself.

        On mine, I had to bridge it out with a piece of wire, then the card powered up. There were also some missing capacitors behind the GPU


        it was the Phantom board that had this problem - these posts are relevant

        PHANTOM
        This is the one with a short on VCC3 supply from the PCIe connector
        I was just going to use my bench supply to send 3.2V into that supply (as per the the voltage I measured on the Palit) when I noticed a bit of a mess in a similar area to where I found the shorted Vcore cap on the Gigabyte. It looked like some spare solder blobs and a probable solder bridge. I cleaned that up with flux and braid and the Short on VCC3 had gone I didn't try replace the six missing components I just powered it up - and it still does not detect. Then I found I still have no VCC3 I can compare with the Palit to work out what components are missing.

        A quick check to see why I still have no VCC3 after removing the short - I found on the Palit where I do have VCC3 I have 0 ohms from Pin 7 PCIe to that voltage rail. But on the Phantom I have 47 ohms. I couldn't see that before because of the short.

        This is now looking like I have an open circuit fuse or a fusible resistor (or just a low value resistor gone high) somewhere connected between pin 7 PCIe and that voltage rail!!

        However at this point I had well and truly had enough of these hateful graphics cards! Why are they giving me so much hassle Fix one thing and then it's another bloody thing aarrrghh!

        So I will look tomorrow when I calmed down. Could be this one will be fixed.


        PHANTOM
        The Phantom GTX 780 I've had something of a result. Despite spending a couple of hours on this, I just could not find why I have 25 ohms (was 47 ohms but it changed for some reason) between pin 7 of PCIe (VCC3) and the voltage rail it should supply on the graphics card. I have a direct connection from PCIi pin 7 to one capacitor on the graphics card but to everywhere else I can see it goes, I have 25 ohms.

        As hard as I looked I can't find a resistor or similar that accounts for the resistance. My best guess is a faulty via causing some resistance???

        So I decided to cobble it. I soldered a wire from the MLCC which was connecting to pin 7 PCIe and soldered the other end to another capacitor on the 3.3V voltage rail on the graphics card - thus 'bypassing' (or shorting out) the 25 ohms.

        I then powered up the card and could tell straight away (because the GPU now warmed up) that I have Vcore!! But the graphics card was still not detecting I was getting the usual beeep bip bip bip same as before That was enough for yesterday.

        Anyway it occurred to me later that really by now I should be getting a picture but maybe the old MSI motherboard I was using as a test rig (MS-7293 which came out of an old Fujitsu tower server PC) was not compatible with the graphics card - like the BIOS couldn't detect it or something. This despite the same test motherboard working OK with a Geforce 7600GS I have.

        The reason for this thought is because I have had problems in the past with machines like Dell and HP not detecting some graphics card when you fit them.

        I had used that motherboard because I had it lying around and it does not have onboard graphics. So anyway I got another old board I have that also has no onboard graphics, an Asus P5B Deluxe.

        I put the Phantom in that - and it detects!!! BUT..... although I now have Vcore (0.94V) and Vram (1.5V) and I get a picture - there are little white dashed lines on it See attached pics.

        Only thing I am thinking now is maybe the six little SMDs on the rear behind the GPU that were missing and/or someone had bodged up with solder (see pic) are actually necessary and causing the messed up video output. I could take these from the Palit and see what the parts should be.

        Or maybe the GPU or RAM are screwed up
        Last edited by dicky96; 04-13-2021, 02:28 AM.
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          #5
          Re: inno3D GTX780 no picture, not recognized

          Originally posted by dicky96 View Post
          I think the 3.3V acts as a standby supply to the GPU BGA itself.
          the 3.3v more of acts as the vcc power for the video bios eprom chip, as u need power to the eprom chip to read the video bios firmware to start the gpu and video card.

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            #6
            Re: inno3D GTX780 no picture, not recognized

            @Chaos..
            From what I've seen looking at Nvidea cards, all the x16 traces from the PCIe slot (the differential signals ones, LVDS?) go directly to the GPU

            So I would expect the only way the PC BIOS can read the Video BIOS is via the GPU - or at least part of the GPU.

            They have at least 4 supply rails and one would be the 3.3V STBY or some voltage, 1.8V or whatever, derived from 3.3V STBY.

            I'm pretty sure this is also the voltage that needs to be present so you get EN asserted on the VRMs... but I could be wrong.
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              #7
              Re: inno3D GTX780 no picture, not recognized

              Video cards don't really have "standby" rails. However, they do have at least one secondary Vcc for the GPU chip, which is responsible for powering the sections of GPU that read the EEPROM/flash chip. This (or these) secondary rail(s) is also what allows video cards to display simple messages, such as "power cable not connected" if the user forgets to plug in the power cable. The secondary Vcc rail(s) is typically powered from 3.3V on the PCI-E connector.

              So essentially, 3.3V is needed for both the card's EEPROM/flash chip and secondary rail for the GPU chip (typically generated from an LDO or two.) Once the GPU chip has read its EEPROM/flash and initialized and communicated with the PC, only then it may send a power signal to its VRM controllers to start all of the main power rails (GPU V_core, RAM V_dd, GPU V_tt.)

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                #8
                Re: inno3D GTX780 no picture, not recognized

                I found the failure. The NCP4206/4208 does not start if there is a missing driver mosfet. I wanted to start the card with just 5 of 6 phases but the phasecontroller doesn't start. So I soldered in a working mosfet and the card is running again.

                Summary: 1 defective SIC780.

                Best regards

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                  #9
                  Re: inno3D GTX780 no picture, not recognized

                  Originally posted by Schorsch87 View Post
                  I found the failure. The NCP4206/4208 does not start if there is a missing driver mosfet. I wanted to start the card with just 5 of 6 phases but the phasecontroller doesn't start. So I soldered in a working mosfet and the card is running again.

                  Summary: 1 defective SIC780.

                  Best regards
                  Nice work! thanks for the update
                  Successfully completed Repairs:


                  Current repairs:

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