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820-2915-B 3 Beep RAM issue

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  • 820-2915-B 3 Beep RAM issue

    Hello,
    this time im working on an 820-2915-B that starts but wont boot up. The screen stays black and it beeps 3 times. I tried different RAM but it did not work. So i measured PP0V75_S0_DDRVTT which should be 0.75V i guess but is is 1.3V. Can this cause the problem? If yes i guess a resistor is blown somewhere because this would explain a higher voltage (a bad cap would short/lower it instead as far as i know). So i measured all resistors on this power rail and all seem to be fine. Just R3250 is 11OHM instead of 10 but i guess this is fine too. NO i dont know what to do next.
    Thank you for any help.
    Felix

  • #2
    Dead U7300 or something is pulling up 0V75 rail, like a short in the RAM slot.

    Comment


    • #3
      I replaced U7300 but still 1.3V on Pin 3 and on Pin 1 of C7360. Ram Slots look fine as far as i can tell.

      Comment


      • #4
        Voltage on C7350 and L7330?

        Comment


        • #5
          C7350: Pin1 1,476V , Pin2 0V

          L7330: Pin1 1,516V , Pin2 1,511V

          Comment


          • #6
            Voltages on pin 1 2 3 5 6 9 of U7300?

            Comment


            • #7
              Voltages on U7300:

              Pin 1: 1.3V
              Pin 2: 1.5V
              Pin 3: 1.3V
              Pin 5: 1.475V
              Pin 6: 1.8V
              Pin 9: 1.5V

              Sometimes the reading is 1.507V instead of 1.5V but i guess my multimeter is a little off and this wont effect anything either.

              Comment


              • #8
                theres SDA and SCL on LP8550. check if these are shorted to ground, check those lines also have 3.4V on them.

                Is it both slots that have the same issue?

                Comment


                • #9
                  SMBUS will be fine as there are 3 beeps. The obvious problem is overvoltage on the 0V75 bus.

                  I cannot find anything from your measurements explaining the issue. What is the resistance to GND on the 1.5V bus?

                  Comment


                  • ALB-Repairs
                    ALB-Repairs commented
                    Editing a comment
                    Yup sorry, i forget SMBUS is one beep not 3.

                • #10
                  Thanks for the help and sorry for my late response. It seems like i´m not able to do any more measurements this year. I´ll get back to this as soon as possible. Sorry for the dumb Question. When talking from the 1.5V bus you mean SMBUS? Should i replace all resistors on that line to be sure they are fine? And if something with my soldering / the new U7300 chip is wrong this should affect other signals on other Pins as well right?
                  Thanks for all your help and happy Holidays!

                  Comment


                  • #11
                    1.5V bus is the one fed by U7300. The problem is already clear and that is the wrong voltage on the 0V75 rail. I have no idea why right now, so check resistance to GND on L7330

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                    • #12
                      Diode mode reading on both pins of L7330 is 0.014V (I hope that is what you mean).
                      But if i plug the charger in i measure on both pins of L7330 1.5V.

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                      • #13
                        0.014 seems very low on this bus. I can compare with a good board tomorrow

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                        • #14
                          Hello,
                          sorry, that i disturb you again. Come back to this if you have time for it. Just want to ask how likely it is that this will work again because the customer asked me again.

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                          • #15
                            Measured L7330 on 3 different boards, 0.109, 0.273 and 0.457. So your 0.014 is way to low and would probably indicate a dead CPU.

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