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MGX7520 onboard graphics problem

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    MGX7520 onboard graphics problem

    Hello, I have a problem with this motherboard mgx 7520.
    This motherboard is from a pinball (revenge from mars); the problem is with the onboard graphics.
    After an inactivity period i can see the post screen but only for more or less one minute, than the screen goes grey, it stay powered on but nothing on the screen. If I use a pci vga card the pc works flawless.
    If I let the mobo without power for a while (i think something has to discarge) then the onboard graphics work again but again only for one minute and then grey monitor.
    I tried changing the power supply, the ram and also the processor, but nothings change.
    This motherboard has a known problem with some capacitors (number 1 to 5), 1000uF 10V, but mine looks good, after an inspection i notice that they was already been changed.
    I tested with the dmm the 5 capacitors and number 1 to 4 give me a value from 3 to 5 kohm, while number 5 only 25-30 ohm. Thinking it was shorted i decided to change all with panasonic FR caps.
    I tested the removed caps with the esr meter and all was good 1000uF and an ESR of 0,14 ohm, testing the pads of the numbered 5 cap on the mobo with the dmm again 25-30 ohm.
    What else can i do? that value is normal or there is a short on the board?
    I'm not an engenier nor a technician, but i have experience in electronics DIY, but without the schematics of the board i can't go further by myself.



    1) 1 to 5 Removed caps
    6) AIC1579CS
    7) 09N05
    8) L1084S
    9) PC97317 - IBW
    10) CX5520
    11) CPU Cyrix GXm-233GP
    Attached Files

    #2
    Re: MGX7520 onboard graphics problem

    Hello, i found another identical mobo, but this one is working.
    I check the number 5 caps with the DMM in ohm mode, and in this board the value is 350 ohm, so completely different from the non working one.
    I think the problem is in this line, but where?

    Comment


      #3
      Re: MGX7520 onboard graphics problem

      Now that you have two identical board a nice way could be to use a thermal camera to look for any hotspots that are not the same between the units.
      "The one who says it cannot be done should never interrupt the one who is doing it."

      Comment


        #4
        Re: MGX7520 onboard graphics problem

        Originally posted by Per Hansson View Post
        Now that you have two identical board a nice way could be to use a thermal camera to look for any hotspots that are not the same between the units.
        I was thinking the same, but i don't have a thermal camera, and i didn't found a cheap one.
        I tried to touch with the hand, but in this way i didn't found differences.

        Comment


          #5
          Re: MGX7520 onboard graphics problem

          I don't think 25 ohms would show up in temperature measurements.

          Can you see what that cap connects to? The CPU takes 2.9V and 3.3V, and I would guess that the Cx5520 runs off the same 3.3V supply. The 3.3V most likely comes from the L1084S.

          Also, check the voltages in both the working and non-working states.

          Comment

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