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    Asus X550LD - not turning on

    Hi all

    I have a Asus X550LD laptop (cpu intel i5 4200u, gpu nvidia 820M) here that refuses to turn on.

    No visible physical or water damage on the board.

    CMOS reset; coin battery is fine; plug is fine (gets 19,5v up until a certain point and 3,3v to the battery charging plug); power button discharge done; still nothing.

    The interesting things that I've noticed:

    -when power button is pressed, all the front LEDs flash once, in sequence and then only the far left one stays on for a second, then turns off as well.
    -i hear a pulsating (cca. once a second) high frequency "whine". when measured on a certain point (forgot which one exactly), the voltage jumps up and down.

    I have the boardview schematic and guide, but don't know how to use them ^^

    Thanks for the help
    Attached Files
    Last edited by krayz; 11-22-2021, 10:01 AM.

    #2
    Re: Asus X550LD - not turning on

    Measure and post the voltage values for:

    1) AC_BAT_SYS

    2) BAT_CON (3v3 is too low for this laptop). Is a known good battery connected?

    3) P_CHG_BATDRV_20

    4) P_CHG_PATH_19V_SHAPE

    5) P_CHG_AC_GATE_20

    6) P_CHG_LX_30

    7) P_CHG_LG_30

    8) P_CHG_HG_30

    9) P_CHG_ACDET_10

    10) P_CHG_ILIM_10

    Comment


      #3
      Re: Asus X550LD - not turning on

      this is all with battery connected

      1) AC_BAT_SYS - 19,5v
      2) BAT_CON - 16,8v
      3) P_CHG_BATDRV_20 - 16,8v
      4) P_CHG_PATH_19V_SHAPE - 19,5v
      5) P_CHG_AC_GATE_20 - 19,5v
      6) P_CHG_LX_30 - 16,8v
      7) P_CHG_LG_30 - 0,2v
      8) P_CHG_HG_30 - 20v
      9) P_CHG_ACDET_10 - 2,66v
      10) P_CHG_ILIM_10 - 0,01v

      Comment


        #4
        Re: Asus X550LD - not turning on

        also correction: whine pulses about three times a sec

        Comment


          #5
          Re: Asus X550LD - not turning on

          10) P_CHG_ILIM_10 - 0,01v
          This does not look correct for the operation.

          See attached. Based on the calculator, this ILIM value should be ~0.75V

          Reference:
          https://ohmslawcalculator.com/voltag...der-calculator

          Review the resistors PR8820 & PR8819. Are they the correct values on the logic board ?

          Confirm the voltage on PR8820 - is one pin truly 3v0 ?

          The +3VA rail is mated to +3VA0 using PSL8101 jumper. The +3VA0 rail is created by the LDO (fixed linear regulator) @ PU8100.

          Confirm that the +3V rail is working so that this voltage divider can create the 0V75 for the ILIM threshold. With the present low value, the charger IC will not enable the battery charging.
          Attached Files

          Comment


            #6
            Re: Asus X550LD - not turning on

            Continued...

            1) Remove all power to the laptop (no adapter & no battery).

            2) Meter in resistance mode.

            Measure & post the resistance for each mosfet
            for:

            source (pins 1-2-3) & drain (5-6-7-8) of PQ8801 (datasheet is attached)
            source (pins 1-2-3) & gate (4) of PQ8801
            gate (4) & drain (5-6-7-8)


            then repeat for PQ8802

            then repeat for PQ8803 (battery mosfet)

            Let us start with the above for the mosfet checks. The ILIM resistors are very important as well.

            Reference (see table):
            http://electronicsbeliever.com/how-t...-is-defective/
            Attached Files

            Comment


              #7
              Re: Asus X550LD - not turning on

              remeasured the resistors

              pr8820 gets 3v on one pin, the rest are 0,01v
              i measured this with voltage mode, one probe on common gnd, and one on the pin

              is diode mode necessary for this?
              i tried to measure with the multimeter on diode(v) mode and i got 0,75v on those test points.

              sorry, i'm still a beginner at this


              another question: is the battery necessary for the laptop to turn on?


              thanks for all your help so far

              Comment


                #8
                Re: Asus X550LD - not turning on

                pr8820 gets 3v on one pin, the rest are 0,01v
                i measured this with voltage mode, one probe on common gnd, and one on the pin
                You are measuring this properly. Be sure that you are in DC volts mode.

                Use the lowest DC volts setting on your meter.

                Given that you can measure 3V, this resistor divider is messed up for some reason.

                Try the following:

                1) Remove all power. Meter in resistance mode.

                2) Place one meter probe at the common junction of these 2 resistors = ILIM pin on the charger IC. The other meter probe to ground.

                What resistance value is being read by the meter ? Based on the very low voltage of 0V01 = 0.01 volts at this resistor based voltage divider, guessing that the charger IC or the resistor @ PR8819 is shorting to ground (or is a very low resistance that is not the required 100k value = 100,000 ohms).

                BTW - Is there a capacitor near this resistor to ground @ PC8802 ?

                Do you have hot air tools for soldering / desoldering ? If you see a capacitor @ PC8802 - remove it and then check the voltage again for the ILIM pin.

                Something linked to the ILIM is tanking the voltage down to this very low value of 0v01.

                is diode mode necessary for this?
                i tried to measure with the multimeter on diode(v) mode and i got 0,75v on those test points.

                another question: is the battery necessary for the laptop to turn on?
                Personally use resistance mode more often to diagnose such cases. Do not believe the battery is required. I know that my son has an Asus where the battery died literally the week after the warranty expired. It was a key fault with the Asus ROG751 model (brick but is a fast unit). Yet, he uses the laptop daily and has been for the past few years for school work.

                Proceed to check the mosfets. I think you have some issues there as well.

                Comment


                  #9
                  Re: Asus X550LD - not turning on

                  Originally posted by mon2 View Post
                  Personally use resistance mode more often to diagnose such cases. Do not believe the battery is required. I know that my son has an Asus where the battery died literally the week after the warranty expired. It was a key fault with the Asus ROG751 model (brick but is a fast unit). Yet, he uses the laptop daily and has been for the past few years for school work.

                  Proceed to check the mosfets. I think you have some issues there as well.
                  Dying batteries in gaming laptops is normal, because of high current drain
                  Last edited by SMDFlea; 11-23-2021, 11:02 AM.

                  Comment


                    #10
                    Re: Asus X550LD - not turning on

                    Dying batteries in gaming laptops is normal, because of high current drain
                    The batteries used by Asus were crap. Many complaints on the net about the battery on the same model. Our son kept the laptop always plugged in so did not expect this fault so 'early'. About to replace the LCD panel on the same - gone pink. Recently arrived from Shenzhen. May just replace the battery now while it is open.

                    Comment


                      #11
                      Re: Asus X550LD - not turning on

                      Originally posted by mon2 View Post
                      The batteries used by Asus were crap. Many complaints on the net about the battery on the same model. Our son kept the laptop always plugged in so did not expect this fault so 'early'. About to replace the LCD panel on the same - gone pink. Recently arrived from Shenzhen. May just replace the battery now while it is open.
                      Having laptop with battery always on charger is best way to short life of battery

                      Comment


                        #12
                        Re: Asus X550LD - not turning on

                        --- mosfets
                        PQ8801
                        source to drain - 6,6 MOhm
                        gate to source - 1 MOhm
                        gate to drain - 560 kOhm

                        PQ8802
                        source to drain - 460kOhm
                        gate to source - 1 MOhm
                        gate to drain - 8 MOhm

                        PQ8803 - behaves strangely, different values on multiple measurements
                        source to drain - 62kOhm (on first measurement 12kOhm, subsequent 62kOhm)
                        gate to source - 0,5 MOhm, 1 MOhm, 0L)
                        gate to drain - 0,5 MOhm, 0L

                        i've measured also the voltage drops between sources and drains on these mosfets, all of them were 0,5v
                        ---

                        - pc8802 cap spot is vacant, i do have air soldering tools though

                        - ILIM pin to GND -> 2,5kOhm

                        edit: nevermind about the pq8803, just saw the resistance section of the guide you posted.
                        Last edited by krayz; 11-24-2021, 09:24 AM.

                        Comment


                          #13
                          Re: Asus X550LD - not turning on

                          i have almost same asus laptop with same problem, mboard: x550lc rev 2.0, x550lb with pulsating coil whining and also indicator lights do the same flash pattern, does it sometimes start but no picture on screen? i managed to get laptop working somehow when bios battery was removed and just plugged the charger in, it posted normally but symptoms came back after 3 or 4 restarts, i repeated the process and it was working again 3 - 4 restarts, try can you start the board like that

                          Comment


                            #14
                            Re: Asus X550LD - not turning on

                            ill give it a shot

                            Comment


                              #15
                              Re: Asus X550LD - not turning on

                              Tried a few times, no go, sadly

                              Comment


                                #16
                                Re: Asus X550LD - not turning on

                                Let's check the USB ports, if there isn't bend pin, shorting 5V to the ground. I'm using USB male connector with a red and black wires, you can measure for the short, and also inject 5V when troubleshooting the short on 5V rail.

                                Comment


                                  #17
                                  Re: Asus X550LD - not turning on

                                  On the use of the repair guide, remove all power (no adapter / no battery).

                                  Review sheets # 6 & 7 of the repair guide. These are DIODE value readings on a known good logic board.

                                  Configure your multimeter to DIODE mode.

                                  Then place RED (yes RED) meter probe to GROUND on the logic board.

                                  Measure each location shown on pages 6 & 7 with the BLACK meter probe.

                                  Compare the values against the document. When you find a severe mismatch on the value(s), post the details here.

                                  Comment


                                    #18
                                    Re: Asus X550LD - not turning on

                                    So I've measured the values of the points in the guide and they are on average cca 0,05v lower than in the guide (this should be within spec right?).

                                    There are only two values that have a larger mismatch:

                                    41. U7002 BUF_PLT_RST#: 0,315v (should be 0,486v)
                                    24. Q3002 SUSWARN#: 0.285v (should be 0,405v)

                                    thats about it.

                                    Comment


                                      #19
                                      Re: Asus X550LD - not turning on

                                      Could it be a superio problem? how does one test it?

                                      Comment


                                        #20
                                        Re: Asus X550LD - not turning on

                                        See attached.

                                        1) Remove PR8819 off the logic board.

                                        2) After the resistor is removed, confirm the resistance of this component while it is off the logic board. It should be ~100k ohms. Post the value.

                                        3) Leave this part off the logic board. Check the resistance to ground of the ILIM pin of PU8800 (charger IC). You can check this at the common junction of PR8819 & PR8820 (point #2 in the attached boardview pic). Post the value.

                                        4) Next, check the resistance of PR8820. Use the meter probes and check the resistance across the 2 pads of PR8820. Your meter should be in a scale higher than 300k to measure this component. This part should be ~300k ohms. Post the value.

                                        5) Remove the battery. Meter in DC volts mode. Power up with adapter. Check the voltage on PR8820, pin # 2. It should be about +3v0. Post the value.

                                        Check the voltage on PR8820, pin # 1. It should also be about +3v0 since the pull-down resistor @ PR8819 is still off the logic board. Post the value.

                                        Only if PR8819 & PR8820 are of the correct value and PR8820 is mated to +3v0, then these 2 resistors will work together to offer a lower voltage than the source +3v0 but certainly should be a non-zero value.
                                        Attached Files

                                        Comment

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