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Asus X550LD - not turning on

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    #21
    Re: Asus X550LD - not turning on

    2) 100k
    3) cca 1k
    4) 4,6k
    5) 0,01v

    pr8820 pin 1 (0,01)
    pr8820 pin 2 (3,3v)

    side note: the pulsating sound is coming from around this area, if that is even important.

    thanks for your help so far

    Comment


      #22
      Re: Asus X550LD - not turning on

      According to the schematic, PR8820 should be a 300k resistor. So either the logic board has a defective resistor at this location or the assembly was made with this change and the schematic was not updated to reflect the new value.

      Locate any resistor that is available like 10k or similar (value is not very critical but try to be in the range of 4k7 to 47k). Solder in place for PR8820.

      Do not have a resistor @ PR8819 on the board.

      Then power up (no battery). What is the voltage reading for the new PR8820, pin # 1 ?

      This will be the same as the ILIM pin analog voltage. It should be ~ +3v but confirm it.

      Attaching a typical charger circuit for the same device that is onboard your logic board. The reference design is also using about 300k for the high side and 100k for the low side for the ILIM function. This equates to about 4A peak support.
      Attached Files
      Last edited by mon2; 11-29-2021, 03:36 PM.

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        #23
        Re: Asus X550LD - not turning on

        only had through hole resistors, so i used one of those - 14,7k

        new readings on pr8820: pin1 0,2v ; pin2 3,3v

        Comment


          #24
          Re: Asus X550LD - not turning on

          Something is wrong @ pin # 1 junction = ILIM pin of the charger.

          Are there any other parts that may be connected to pin # 1 of PR8820 ?

          Or is the charger IC, pin #10 the only other connection ?

          Specifically, pin # 1 of PR8820 should be ~ +3V0 and it is not. Some other factor is causing this pin to go to 0V which is not correct.

          If you are comfortable with the idea, you could desolder the charger IC and check pin # 1 voltage again. Perhaps the charger IC, pin #10 (ILIM) has a fault and is causing this issue.

          You could apply flux onto the charger IC and hot air to make the chip dance to reflow the IC. Use low air pressure but higher heat so that parts do not go flying off the PCB. Then check the voltage again for pin #1 of PR8820.

          Is there a capacitor @ PC8802 ? If yes, remove it and check again. The schematic shows '@' in the label suffix so usually this means the part is NOT stuffed during the PCB assembly process.

          Comment


            #25
            Re: Asus X550LD - not turning on

            I'll try reflowing the IC first. what temperature should i use?

            Comment


              #26
              Re: Asus X550LD - not turning on

              On our tool, due to the heavy ground plane (copper) on the PCB, we use 400-500C and 30-40% air pressure. Apply flux and use the tweezers to gently nudge the part. Never force the move. When the part is hot enough, it will move with a gently nudge of the tweezers and then bounce back to the pads, naturally. This should be enough to reflow the part. You can increase the air pressure if needed but keep the nozzle on top surface and around the perimeter of the part only. Again, so other parts do not go flying off the board.

              If you have kapton tape, apply it on the nearby parts for the same reason.

              Take your time and see if this fixes the ILIM fault. In the end, the single resistor you have in place should show ~ +3v, unless the part or the ILIM pin is somehow pulling this line down to 0V.

              ILIM is an INPUT to the charger IC so it should not be loading down the pin (unless it is defective).

              Comment


                #27
                Re: Asus X550LD - not turning on

                So I tried to reflow - no difference. Then I took the charger IC off the board.

                I remasured the two resistors PR8820 and PR8819 at 100k and 300k and put them back (on the board values change, which is normal as I understand?)

                Can the board be plugged in without it, since the IC controls the charging?

                Comment


                  #28
                  Re: Asus X550LD - not turning on

                  Yes, if you are comfortable with the reflow and soldering, you can power up again.

                  Post the voltage again for the ILIM junction (PR8820 & PR8819).

                  What is the voltage value?

                  Comment


                    #29
                    Re: Asus X550LD - not turning on

                    Welp, that didn't go according to plan (there was smoke involved )

                    I removed the battery immediately, hopefully no (serious) damage.

                    Checked continuity from each IC pin to immediate connections and everything was OK. So I have no idea what this is all about ^^

                    Comment


                      #30
                      Re: Asus X550LD - not turning on

                      https://www.badcaps.net/forum/showpo...02&postcount=2

                      2.7. Don't apply power to the board with missing components
                      As a general rule, if a component is on the board, it's because it's useful for something. Engineers don't like adding a bunch of useless components on the board, it's harder to draw the schematics and route on the PCB.
                      Some of them can be removed without creating problem if power is applied, but others can kill the board with no possibility of repair.
                      For example, if you remove a buck controller or a MOSFET driver, the MOSFET gates will be floating. They'll charge up enough so that the MOSFET turns on. Of course, you don't want the 19V from the main power rail to go straight through the CPU VCore MOSFET to the CPU.
                      OpenBoardView — https://github.com/OpenBoardView/OpenBoardView

                      Comment


                        #31
                        Re: Asus X550LD - not turning on

                        Suggest to replace:

                        a) the charger IC

                        b) the 2 resistors linked to the ILIM leg

                        Study each part connected to the charger IC to look for any possible damage. There should not have been any smoke from the work so far.

                        Case # 1:

                        The resistors for ILIM are onboard. The charger will continue behave like before.

                        Case # 2:

                        The resistors for ILIM are removed. That was not this case but ILIM is an analog voltage where a positive voltage translates to higher current for the battery charging. Respectively, without resistors, there would be 0V = no charging current = nothing to do.
                        Last edited by mon2; 12-01-2021, 04:41 PM.

                        Comment


                          #32
                          Re: Asus X550LD - not turning on

                          OK, I've ordered a new charging IC (cheap, but it will take some time to get here i suspect).

                          In the meantime I'll browse around the forum and try to learn more about charging/power circuits and how they function.

                          One question: you said ILIM is an input. What would happen if voltage was injected to ILIM pin with a lab. pow. supply?

                          Comment


                            #33
                            Re: Asus X550LD - not turning on

                            Me again, got the components and restarted my work.

                            I've replaced the PU8800 IC. Checked the continuity, looked good. Also replaced the surrounding resistors with new ones (with correct values).

                            I plugged in the battery and charger - now it wasn't only smoke ... a MOSFET burned, literally (i instantly unplugged and checked around with the microscope - no other damage visible). The MOSFET was PQ8805.

                            I reconnected the charger and I checked the voltage on P_CHG_ILIM_10 and it showed ~3V (without the battery), and about 0,7v voltage drop to ground, so at least there is progress here. Voltage to PQ8805 source is 19,5V.

                            LEDs come on as before, but laptop doesn't want to boot.

                            I'm thinking about shorting drain and source on PQ8005 to see if it really was to blame.

                            Comment


                              #34
                              Re: Asus X550LD - not turning on

                              OK... so I bridged the MOSFET (temporarily, I'll order a new one) and plugged in the charger - the laptop would still not power on.

                              Then I removed the CMOS battery, pressed the power button and the laptop powered on: first and last LED power on and stay on, and the fans start spinning (yay). It works like this with the CMOS battery back in as well. I'm doing all this without the laptop battery plugged in for now.

                              Voltages look normal (the problem is I don't really know what did it - the charger IC replacement or the MOSFET removal).

                              I still have no picture / boot sadly. Now I'm thinking there really is something up with the 'superIO' or BIOS IC...

                              Luckily, when I ordered the charger IC, I ordered the super IO as well, just in case, cause it was pretty cheap (2$). But soldering it on the motherboard seems like a nightmare, so I'll leave that for last.

                              Any tips or help would be appreciated

                              thanks

                              Comment


                                #35
                                Re: Asus X550LD - not turning on

                                What are the missing voltage on the big Gray coils? On the ram slot check the voltage pin 30 with the ram

                                Comment


                                  #36
                                  Re: Asus X550LD - not turning on

                                  big coils:
                                  18,5v
                                  1v
                                  1,5v
                                  1,7v
                                  1,3v

                                  i have onboard ram only

                                  pin 30 on ram slot: 0,4v

                                  Comment


                                    #37
                                    Re: Asus X550LD - not turning on

                                    Originally posted by krayz View Post
                                    big coils:
                                    18,5v
                                    1v
                                    1,5v
                                    1,7v
                                    1,3v

                                    i have onboard ram only

                                    pin 30 on ram slot: 0,4v
                                    In your MB they are 8 Gray coils note the voltage near the coils , so you don’t have a extra ram to check? Q602 voltage?
                                    Attached Files
                                    Last edited by Techtiger; 03-18-2022, 04:04 AM.

                                    Comment


                                      #38
                                      Re: Asus X550LD - not turning on

                                      No extra RAM modules sadly

                                      Here are the measurements in picture form

                                      Comment


                                        #39
                                        Re: Asus X550LD - not turning on

                                        Originally posted by krayz View Post
                                        No extra RAM modules sadly

                                        Here are the measurements in picture form
                                        Do you have a USB key board if so attached the screen power and see if the
                                        num lock is working or not ? Check the voltage U7002 BUF_PLT_RST# H DRAM PWRGOOD
                                        Last edited by Techtiger; 03-19-2022, 04:32 AM.

                                        Comment


                                          #40
                                          Re: Asus X550LD - not turning on

                                          Num lock doesn't work on usb keyboard when connected and powered on.
                                          I can't seem to find H_DRAM_PWRGOOD on the schematic. Is it called by some other name?

                                          U7002:


                                          The hottest part of the board are the RAM modules...

                                          Thanks so far
                                          Last edited by krayz; 03-19-2022, 01:29 PM. Reason: img link fix

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