Announcement

Collapse
No announcement yet.

Toshiba Satellite L750D - 19v missing on the main power rail

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

    Toshiba Satellite L750D - 19v missing on the main power rail

    Hi, i'm trying to fix this notebook with the 19v missing on the main power rail.

    It's an old Toshiba Satellite L750D.
    The CPU (an AMD Phenom II) can be removed but the GPU is soldered.
    Mainboard model: DABLCDMB8E0 REV E.

    The notebook isn't mine, and it was in pretty bad condition.
    Other than be full of dust and with broken parts, i also found this problems:

    1) the DDR3 ram was half-disconnected, and 1 smd capacitor near the memory chips seems burned (photo n1);
    2) in the mainboard another one smd capacitor was not soldered, but near the original position (n2).

    I cleaned all with IPA, soldered again the disconnected capacitor, removed the burned ram, the CPU (i don't know if still good or not) and all the other things.

    The power supply it's fine (19v when is not connected to the mainboard).
    Connected to the mainboard, i can hear the power supply "clicking", and the voltage drop at 2-2.5v (unstable).

    After many minutes, only the up-left part of the board become a bit hot (both sides A-B), and seems that is one of the big mosfet that heat the pcb.
    But still, nothing that is "burning hot".... ( photo n3 "mainboard zoom SIDE A").

    In that mosfet, the voltage is 2-2.5v in input (right), and 1-1.2v in the output (left).
    Around the board, stuffs near the cpu socket, gpu etc are cold, with 0v or 0.100-0.300v.

    In the photo n4 "plus signal SIDE B" (taked after i dismantled the notebook) i "painted" where the plus DC signal start in one side of the board (the PC24 capacitor was the one disconnected that i soldered again).

    So + +, PF2 fuse, then PL1/PL2, PD4, PC39, PD3, PD5, PR38, PQ2, and then other things until the ISL88731C battery chip.
    Other than the fuse that is good, i can't be sure about all the other parts.

    Starting from the right side of PD3, there is a resistance of about 200 ohms from the left side (and the plus start). Maybe is ok but again i'm not sure about it.

    I did a sort of "schematic" for both sides (n3 - n4), and also tested some capacitors with the ohms values to ground.
    Say me if more details is needed, or what tests i have to do.

    I'm new in the "component level repair" world, just watched some videos on yt, read of similar problems in the internet and also the beginner's guides here.

    Honestly, i learned few stuffs starting from 0, but still can't find the problem or how to test the main power rail correctly in this mainboard.

    I disconnected some capacitors near that battery chip and the two big mosfets in the other side of the board.
    The capacitors that i tested are all fine but i'm not sure about how to test the 2 big mosfet.

    The notebook is old and not important, but i really want try to fix it, like a personal challenge!

    Thanks for the help and sorry if i did any errors! ^^"
    Attached Files

    #2
    Re: Toshiba Satellite L750D - 19v missing on the main power rail

    Hi first thing what you must do is measure current resistor to ground how much resistance do you have thete. The resistance is measure without power, memory , cmos battery and etc...

    Comment


      #3
      Re: Toshiba Satellite L750D - 19v missing on the main power rail

      Originally posted by Stevedb View Post
      Hi first thing what you must do is measure current resistor to ground how much resistance do you have thete. The resistance is measure without power, memory , cmos battery and etc...
      Hello!
      All the ohms measures that i did in the photos was without anything connected other than the board itself!

      About what you asked, in this mainboard there are 2 current resistors...

      1) PR150 on side A, multimeter with - to ground and + to CR ---> 54k Ω

      2) PR38 on side B, multimeter like before ---> 289k Ω

      Thanks for the help!

      Comment


        #4
        Re: Toshiba Satellite L750D - 19v missing on the main power rail

        I desoldered the two big mosfet again (PQ18 and PQ17).
        They seems to work fine (i can close / open them). Also swapped them but nothing changed. The one that become hot is still in the PQ18 position.

        Also with the power on, the board is cold everywhere, except for that area (up-left) near the power connector and the ram slots (both sides).

        This means that the faulty component is located there or can also be in the other parts of the board?

        Comment


          #5
          Re: Toshiba Satellite L750D - 19v missing on the main power rail

          Your main (19V) power rail is shorted to ground. First check out of the circuit caps PC8, PC9, PC10, PC132, PC134.
          ----------------------------------------------------------------------------------------------------------------------------------------------------------
          All donations to Badcaps are welcome.
          Become a Badcaps supporter
          >>>>> click on this link to donate <<<<<
          Thanks to all supporters.
          ----------------------------------------------------------------------------------------------------------------------------------------------------------
          Doctrina est fructus dulcis, radicis amarae.
          .

          Comment


            #6
            Re: Toshiba Satellite L750D - 19v missing on the main power rail

            Originally posted by Vesko356 View Post
            Your main (19V) power rail is shorted to ground. First check out of the circuit caps PC8, PC9, PC10, PC132, PC134.
            Tested them disconnected from the pcb. All seems good, no beep from the multimeter, no "low resistence", and it's possible to read the farad value.

            But all that area is connected to ground also without the caps connected...
            Also PC123, PC126, PC127, and C559 are fine.

            The two little mosfets PQ14 and PQ16 didn't have source / drain / gate shorted.
            In diode mode there is like 0.450-0.500v from source (pin 1-2-3) to drain. Gate to drain (pin 4 with pin 5-6-7-8) is near 1v.

            That's fine right? Thanks for the help! ^^
            Last edited by AidenX; 05-30-2022, 12:22 AM.

            Comment


              #7
              Re: Toshiba Satellite L750D - 19v missing on the main power rail

              Do you have a schematic for your machine? Upload it here if you have one. There is no point in continuing to remove components at random, it's best to inject 1 volt / 1 amp into the main power rail, and find out which component is heating up. If you have a FLIR camera you can locate it very easily.
              ----------------------------------------------------------------------------------------------------------------------------------------------------------
              All donations to Badcaps are welcome.
              Become a Badcaps supporter
              >>>>> click on this link to donate <<<<<
              Thanks to all supporters.
              ----------------------------------------------------------------------------------------------------------------------------------------------------------
              Doctrina est fructus dulcis, radicis amarae.
              .

              Comment


                #8
                Re: Toshiba Satellite L750D - 19v missing on the main power rail

                Look like PQ18 is the first mosfet, when you removed PQ18, does the main connector and GND still shorted?

                Comment


                  #9
                  Re: Toshiba Satellite L750D - 19v missing on the main power rail

                  Originally posted by Vesko356 View Post
                  Do you have a schematic for your machine? Upload it here if you have one. There is no point in continuing to remove components at random, it's best to inject 1 volt / 1 amp into the main power rail, and find out which component is heating up. If you have a FLIR camera you can locate it very easily.
                  No schematic...Also as i said it's the first time that i try to fix a dead notebook motherboard so i don't have any FLIR camera (they aren't cheap! xD).

                  But i have a simple DC Power Supply. I already tried to inject 1V-1A but with just touching the board i didn't find any component that become too hot...
                  The only board area that is heating up a little is the same when the regular power supply is connected (post #4 and photo n3).

                  Maybe i tested it wrong. Can you say me where i have to put the plus of the DC power supply (like in the current resistor PR150 or another component) ?


                  Originally posted by z2168235 View Post
                  Look like PQ18 is the first mosfet, when you removed PQ18, does the main connector and GND still shorted?
                  Hi! The resistence between the + + pins of the power connector and the ground of the board is about 300k ohms with PQ18 soldered.

                  Do you mean this? If yes i can test again it without PQ18....but when i desoldered the two big mosfet (PQ18 and PQ17) both had the same values also in diode mode (and the open/close thing worked).

                  Thanks! ^^
                  Last edited by AidenX; 05-30-2022, 11:16 AM.

                  Comment


                    #10
                    Re: Toshiba Satellite L750D - 19v missing on the main power rail

                    Originally posted by AidenX View Post

                    Maybe i tested it wrong. Can you say me where i have to put the plus of the DC power supply (like in the current resistor PR150 or another component) ?
                    See the attached image:
                    Attached Files
                    ----------------------------------------------------------------------------------------------------------------------------------------------------------
                    All donations to Badcaps are welcome.
                    Become a Badcaps supporter
                    >>>>> click on this link to donate <<<<<
                    Thanks to all supporters.
                    ----------------------------------------------------------------------------------------------------------------------------------------------------------
                    Doctrina est fructus dulcis, radicis amarae.
                    .

                    Comment


                      #11
                      Re: Toshiba Satellite L750D - 19v missing on the main power rail

                      Originally posted by Vesko356 View Post
                      See the attached image
                      Mmm, that part of the mosfet is connected to the ground...so both sides of the DC power supply will be connect to ground O.o

                      Tested it, and the DC voltage drop at 0.03V, still 1A, but with C.C mode instead of C.V.

                      It's normal?

                      Comment


                        #12
                        Re: Toshiba Satellite L750D - 19v missing on the main power rail

                        Originally posted by AidenX View Post
                        i don't have any FLIR camera (they aren't cheap! xD).
                        If you like to play with electronic repair, FLIR camera is a must have tool, yes they are not cheap, but you can buy FLIR equipped phone as a CAT S60 for example, the price of these second hand is about 100-150 euro, and the built in thermal camera quality is pretty good. Meanwhile you can use alcohol to find the fault. The alcohol will evaporate first at the hot faulty component, so you can spot the fault easily this way.
                        ----------------------------------------------------------------------------------------------------------------------------------------------------------
                        All donations to Badcaps are welcome.
                        Become a Badcaps supporter
                        >>>>> click on this link to donate <<<<<
                        Thanks to all supporters.
                        ----------------------------------------------------------------------------------------------------------------------------------------------------------
                        Doctrina est fructus dulcis, radicis amarae.
                        .

                        Comment


                          #13
                          Re: Toshiba Satellite L750D - 19v missing on the main power rail

                          Originally posted by AidenX View Post
                          Mmm, that part of the mosfet is connected to the ground...
                          No, this is your (shorted) main power rail. Something is shorting the rail to ground, this is the reason for the problem in your case. Тhe input mosfet can never be connected to ground, so this is not the ground pad.
                          ----------------------------------------------------------------------------------------------------------------------------------------------------------
                          All donations to Badcaps are welcome.
                          Become a Badcaps supporter
                          >>>>> click on this link to donate <<<<<
                          Thanks to all supporters.
                          ----------------------------------------------------------------------------------------------------------------------------------------------------------
                          Doctrina est fructus dulcis, radicis amarae.
                          .

                          Comment


                            #14
                            Re: Toshiba Satellite L750D - 19v missing on the main power rail

                            Originally posted by Vesko356 View Post
                            If you like to play with electronic repair, FLIR camera is a must have tool, yes they are not cheap, but you can buy FLIR equipped phone as a CAT S60 for example, the price of these second hand is about 100-150 euro, and the built in thermal camera quality is pretty good. Meanwhile you can use alcohol to find the fault. The alcohol will evaporate first at the hot faulty component, so you can spot the fault easily this way.
                            Yes yes it will be really helpful...
                            Maybe in the future if i will find more mainboard to repair, but for now is just one and i don't want to pay 100-150€ for "try to fix" an old notebook.
                            So i can only try to burn it with the things that i have! XD

                            Originally posted by Vesko356 View Post
                            No, this is your (shorted) main power rail. Something is shorting the rail to ground, this is the reason for the problem in your case. Тhe input mosfet can never be connected to ground, so this is not the ground pad.
                            Mmm, what i can do so? Keep the DC power supply in that mode for a while? Or that drop at 0.03V in C.C mode means that also it goes to protection mode for the board short?

                            Comment


                              #15
                              Re: Toshiba Satellite L750D - 19v missing on the main power rail

                              Originally posted by AidenX View Post
                              Mmm, what i can do so? Keep the DC power supply in that mode for a while?
                              Yes of course, this is the idea, keep the positive probe connected to the line until you find which component is heating up.


                              Originally posted by AidenX View Post
                              Or that drop at 0.03V in C.C mode means that also it goes to protection mode for the board short?
                              It is normal the voltage to drop because you have a dead short somewhere (most probably shorted cap) in the line, but the amp meter (at the bench power supply) should show constant draw of 1.0 A. If it's cut the power (goes in protection -i.e clicking and the amper meter is fluctuating) it's not suitable for this type of test, but since it is CC/CV one it should be OK, but I don't know, you have to tell me - the bench supply is in front of you, not in front of me.
                              ----------------------------------------------------------------------------------------------------------------------------------------------------------
                              All donations to Badcaps are welcome.
                              Become a Badcaps supporter
                              >>>>> click on this link to donate <<<<<
                              Thanks to all supporters.
                              ----------------------------------------------------------------------------------------------------------------------------------------------------------
                              Doctrina est fructus dulcis, radicis amarae.
                              .

                              Comment


                                #16
                                Re: Toshiba Satellite L750D - 19v missing on the main power rail

                                Originally posted by Vesko356 View Post
                                Yes of course, this is the idea, keep the positive probe connected to the line until you find which component is heating up.
                                Ok!

                                Originally posted by Vesko356 View Post
                                It is normal the voltage to drop because you have a dead short somewhere (most probably shorted cap) in the line, but the amp meter (at the bench power supply) should show constant draw of 1.0 A. If it's cut the power (goes in protection -i.e amper meter is fluctuating) it's not suitable for this type of test, but since it is CC/CV one it should be OK, but I don't know, you have to tell me - the bench supply is in front of you, not in front of me.
                                Yes, it's stable at 1A, but not in CV mode anymore when i put the plus in that point xD

                                I will try to keep it for a while!

                                The problem can be anywhere in the board or there is some "logic line" that i can follow (or parts of the board that can be excluded) ?

                                Comment


                                  #17
                                  Re: Toshiba Satellite L750D - 19v missing on the main power rail

                                  Originally posted by AidenX View Post
                                  Ok!



                                  Yes, it's stable at 1A, but not in CV mode anymore when i put the plus in that point xD

                                  I will try to keep it for a while!

                                  The problem can be anywhere in the board or there is some "logic line" that i can follow (or parts of the board that can be excluded) ?
                                  The main 19V power line is present on most of the surface of the motherboard, that's why it's main , so the short can be anywhere, there is of course a logical line that can be followed, but as you progress with your knowledge over the time you will understand the logic yourself, for now keep the line under 1V/1A power until you find the hot area with your fingers (the component causing the short can heat up considerably, so be careful), than use the alcohol to locate the exact (shorted) component.
                                  ----------------------------------------------------------------------------------------------------------------------------------------------------------
                                  All donations to Badcaps are welcome.
                                  Become a Badcaps supporter
                                  >>>>> click on this link to donate <<<<<
                                  Thanks to all supporters.
                                  ----------------------------------------------------------------------------------------------------------------------------------------------------------
                                  Doctrina est fructus dulcis, radicis amarae.
                                  .

                                  Comment


                                    #18
                                    Re: Toshiba Satellite L750D - 19v missing on the main power rail

                                    Originally posted by Vesko356 View Post
                                    The main 19V power line is present on most of the surface of the motherboard, that's why it's main , so the short can be anywhere, there is of course a logical line that can be followed, but as you progress with your knowledge over the time you will understand the logic yourself, for now keep the line under 1V/1A power until you find the hot area with your fingers (the component causing the short can heat up considerably, so be careful), than use the alcohol to locate the exact (shorted) component.
                                    Still nothing, all cold :'c

                                    Maybe because the dropped voltage of 0.3V is too low?
                                    I can try it with a bit more amp? All the big chips are cold also (gpu, south & northbridge, super I/O, etc...) and the cpu is disconnected.

                                    EDIT:
                                    I wrote 0.03V before and also in the other post, but was a "write error" xD.
                                    It's 00.3 V (the range is 0.1v - 30v, it doesn't have the .0x unit, idk why i wrote another thing before....).

                                    Sorry!
                                    Last edited by AidenX; 05-30-2022, 03:30 PM. Reason: fixed voltage error

                                    Comment


                                      #19
                                      Re: Toshiba Satellite L750D - 19v missing on the main power rail

                                      Originally posted by AidenX View Post
                                      Still nothing, all cold :'c

                                      Maybe because the dropped voltage of 0.3V is too low?


                                      EDIT: i wrote 0.03V before and also in the other post, but was an error xD. It's 0.3V!
                                      I have already said that the voltage drop is completely normal in your case because there is a very low resistance in the circuit, i.e. short circuit. No one has repealed Om's law yet, so don't worry.
                                      Originally posted by AidenX View Post
                                      I can try it with a bit more amp? All the big chips are cold also (gpu, south & northbridge, super I/O, etc...) and the cpu is disconnected.
                                      Yes, you can increase a bit the amps (but not the voltage) to let's say 2A and try to locate the warming area again.
                                      ----------------------------------------------------------------------------------------------------------------------------------------------------------
                                      All donations to Badcaps are welcome.
                                      Become a Badcaps supporter
                                      >>>>> click on this link to donate <<<<<
                                      Thanks to all supporters.
                                      ----------------------------------------------------------------------------------------------------------------------------------------------------------
                                      Doctrina est fructus dulcis, radicis amarae.
                                      .

                                      Comment


                                        #20
                                        Re: Toshiba Satellite L750D - 19v missing on the main power rail

                                        Originally posted by Vesko356 View Post
                                        I have already said that the voltage drop is completely normal in your case because there is a very low resistance in the circuit, i.e. short circuit. No one has repealed Om's law yet, so don't worry.
                                        Yes yes, what i tried to say is that maybe 0.3v (instead of the 1v that "we asked") is low for burning the bad cap or the bad component xD.

                                        I will try with a bit more amp as you said, thanks!

                                        Comment

                                        Working...
                                        X