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Dell Latitude E5450 LA-A901P no BIOS voltage

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    #1

    Dell Latitude E5450 LA-A901P no BIOS voltage

    Hello.

    I'm trying to toubleshoot a Dell Latitude E5450 that, at first, did not have any sign of life.
    Charger would go into protection mode and I was able to find a bad cap (PC717 in the boardview file attached). I removed it and now I have a white light on power button, but it turns on and off, after about 15 seconds.
    I can find 19V, 5V and 3.3V coils but I could not find 3.3V in the BIOS chip (this model has just one).
    In the schematic (also attached) I can see the BIOS is component UC2 and 3.3V should come from +3.3V_SPI. Is that right?



    But I cannot find 3.3V on any of the connected points the boardview shows me.

    Also I have no voltage on the following components.



    These SPI_PCH_DO2 and SPI_PCH_DO3 are on the component JSPI1, which has no voltage on any PIN also, neither on those RC components.



    Well... after that I managed to trace the component UZ8, where I cannot find 3.3V on pins 13 and 14.



    So... what should I look for, now?
    What did I miss and what did I do wrong?
    ANY help is much appreciated.
    Thank you.
    Attached Files
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    #2
    Re: Dell Latitude E5450 LA-A901P no BIOS voltage

    Hi, what voltages do you have on pins 1, 3 and 4 of UZ8?

    Comment

      #3
      Re: Dell Latitude E5450 LA-A901P no BIOS voltage

      Besides pins mentioned by#jarotech,measure voltage on pin5 also. Resistance to GND on pin13-14 of UZ8?

      Comment

        #4
        Re: Dell Latitude E5450 LA-A901P no BIOS voltage

        Originally posted by jarotech View Post
        hi, what voltages do you have on pins 1, 3 and 4 of uz8?
        1 - 3.3v
        2 - 3.3v
        3 -
        4 - 5
        5 - 3.3v
        6 - 3.3v
        7 - 3.3v
        8 - 3.3v
        9 - 3.3v
        10 - 8.9v
        11 -
        12 -
        13 -
        14 -

        Comment

          #5
          Re: Dell Latitude E5450 LA-A901P no BIOS voltage

          Originally posted by mcplslg123 View Post
          Besides pins mentioned by#jarotech,measure voltage on pin5 also. Resistance to GND on pin13-14 of UZ8?
          340k, on both pins.

          Comment

            #6
            Re: Dell Latitude E5450 LA-A901P no BIOS voltage

            You have 0V on pin 3 (ON1), so UZ8 is not enabled for output at pins 13 and 14 (VOUT1). Measure the resistance to ground on pin 3.

            Comment

              #7
              Re: Dell Latitude E5450 LA-A901P no BIOS voltage

              Originally posted by jarotech View Post
              you have 0v on pin 3 (on1), so uz8 is not enabled for output at pins 13 and 14 (vout1). Measure the resistance to ground on pin 3.
              93k.

              Comment

                #8
                Re: Dell Latitude E5450 LA-A901P no BIOS voltage

                You should have the same resistance on pin 5.

                Comment

                  #9
                  Re: Dell Latitude E5450 LA-A901P no BIOS voltage

                  Originally posted by JaroTech View Post
                  You should have the same resistance on pin 5.
                  A little higher. 99.3K.

                  Comment

                    #10
                    Re: Dell Latitude E5450 LA-A901P no BIOS voltage

                    Sorry but it's bedtime for me, I'll continue tomorrow.

                    Comment

                      #11
                      Re: Dell Latitude E5450 LA-A901P no BIOS voltage

                      Pin 5 is connected to RPE10 pin 4. And I have 3.3V on it.
                      Pin 3 is connected to RPE10 pin 3 and I have nothing on it.

                      Comment

                        #12
                        Re: Dell Latitude E5450 LA-A901P no BIOS voltage

                        Originally posted by JaroTech View Post
                        Sorry but it's bedtime for me, I'll continue tomorrow.
                        No problem.
                        Thanx.

                        Comment

                          #13
                          Re: Dell Latitude E5450 LA-A901P no BIOS voltage

                          Check resistance between pin 6 & 3 of RPE10. Should be 100K. If the resistance between these pins is fine, then you need to head towards SIO's basic requiremnts as A_ON comes from SIO. Remove UZ8 and see if you get voltage on pin3-This will give us an idea whether problem lies in +3.3V_M rail or not.

                          Comment

                            #14
                            Re: Dell Latitude E5450 LA-A901P no BIOS voltage

                            Originally posted by mcplslg123 View Post
                            Check resistance between pin 6 & 3 of RPE10. Should be 100K. If the resistance between these pins is fine, then you need to head towards SIO's basic requiremnts as A_ON comes from SIO. Remove UZ8 and see if you get voltage on pin3-This will give us an idea whether problem lies in +3.3V_M rail or not.
                            91.4K. Would say it's fine? Should I proceed to remove UZ8 and check?

                            Comment

                              #15
                              Re: Dell Latitude E5450 LA-A901P no BIOS voltage

                              Yes, it is close to 100k and is fine.

                              Comment

                                #16
                                Re: Dell Latitude E5450 LA-A901P no BIOS voltage

                                Removed it and now I have 3V on pin 3, on component RPE10.

                                Comment

                                  #17
                                  Re: Dell Latitude E5450 LA-A901P no BIOS voltage

                                  Alright, so you found the short, UZ8 pin 3 is shorted to ground, you need to replace the chip. You have two options, you can replace with APE8990GN3B on page 38 or with TPS22966 on page 4, they are equivalent.

                                  Comment

                                    #18
                                    Re: Dell Latitude E5450 LA-A901P no BIOS voltage

                                    Originally posted by JaroTech View Post
                                    Alright, so you found the short, UZ8 pin 3 is shorted to ground, you need to replace the chip. You have two options, you can replace with APE8990GN3B on page 38 or with TPS22966 on page 4, they are equivalent.
                                    Could I replace it for a EM5209? I found it on an Acer board and this site says it has "similar description".
                                    https://www.alldatasheet.net/datashe.../EM5209VF.html

                                    Comment

                                      #19
                                      Re: Dell Latitude E5450 LA-A901P no BIOS voltage

                                      The general description seems to be similar, you can try it.

                                      Comment

                                        #20
                                        Re: Dell Latitude E5450 LA-A901P no BIOS voltage

                                        Originally posted by JaroTech View Post
                                        The general description seems to be similar, you can try it.
                                        Done it. Exact same readings.
                                        No voltage on pin 3, no voltage on BIOS. And lost the voltage that appeared on RPE after removing the other one.

                                        Comment

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