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Samsung NP365E5C random power off

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    Samsung NP365E5C random power off

    Hello. I am trying to diagnose a laptop. It is a laptop I used daily about 1 or 2 years ago, util I bought another one. So I set it aside and let guests use it. Before setting it aside, it worked perfectly, I could play my normal games on it (MTG Atrena) which isnt too demanding, and it would never fail.

    Now, when using it, I will get random power offs, it just powers completley off, kind of what happens when a laptop overheats, but I can rule out overheating, I'll explain in a minute. It turns off completley randomly, normally it was always used by a guest to play MTG Arena with me, so when it shut off we just thought it was overheating, waited then started it up again. But now we use it for more than just games, and we have gotten shut offs while just writing a word document, so I can see it isn't just because we were playing.

    [How I ruled out overheating]
    I can rule out overheating after various tests. I have changed the thermal compund to arctic mx4, then while running a stress test, I probed the back of the processor (at the motherboard) and the heat sink (by the fan) and both temperatures were within 1°C, indicating that the heat sink is in fact working. Plus during stress tests, I never get a power off, if it passes a certain temperature the screen will go blank, that's another issue though, this never happens while gaming, only with stress test at maximum power.

    Now I am good at finding faulty components, I can read a schematic and have tools to do so (I repair video game consoles and occasionally laptop motherboards), but I just cant find the issue since it is completly random. If it were persistent I could trace down the issue, but being that it's on for a random time then shuts off and can be immediatley turned back on, I just can't find the issue. There seems to be no power loss from the adaptor since the "plugged-in" light never turns off. But the computer has no battery, so that is the only thing I can not rule out since I have no battery as a backup power source. But I have yet to see any power spikes or outages on the oscilloscope.

    Is there anything you can suggest to check?
    Thanks for any help

    #2
    Re: Samsung NP365E5C random power off

    I am starting to believe this might be a temperature issue. The last two days here we have been at about 20°C inside, and I have only had it turn itself off once. The issues were happening more when we were at 28°C inside.

    But even so, why can´t I make it fail? If I run a stress test the screen goes black at high temps, not turn off. Plus I have tried heating a little with a controlled heat gun, and the effect I got was it turning off, BUT in order to turn it back on I had to unplug the charger and plug it back in. This is not the same as when I get the random shut off.

    I have yet to make it fail on demand, only randomly while using it.

    Side note. I had wired the fan to be on at 100% power during the days it was failing more, this did not help at all. I even got a power off 5 minutes into turning it on once, the temp never seemed to get above 60°C in "speedfan". Durign stress tests with fan on auto I can get up to almost 80°C without the screen going black or turning off. After 80°c is when it goes black, but stays on.

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      #3
      Re: Samsung NP365E5C random power off

      Well no one has responded, but just to let you know, It definitely is NOT an overheating issue. I just turned it on after a few weeks of not using it, it turned on, got into windows, lasted 10 seconds then shut off. The motherboard under the processor wasn't even warm, and we are at 16 degrees Celsius inside.

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        #4
        Re: Samsung NP365E5C random power off

        Hi I think you better measure voltage on all coils and resistor value on all coils and write it down on hd picture from the board. Then can somebody help you.

        Good luck

        Best regards
        Steve

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          #5
          Re: Samsung NP365E5C random power off

          I just flashed the bios externally with a clean one, and it did not help, it lasted 20 minutes before shutting off. Plus I had to press the power button 3 times to get it to turn back on. I am between it being the EC or the processor itself. But I have no experience with either failing like this.

          Comment


            #6
            Re: Samsung NP365E5C random power off

            Originally posted by Stevedb View Post
            Hi I think you better measure voltage on all coils and resistor value on all coils and write it down on hd picture from the board. Then can somebody help you.

            Good luck

            Best regards
            Steve
            Thanks for the reply. I will do that when I get some extra time.

            Comment


              #7
              Re: Samsung NP365E5C random power off

              Your motherboard should be at the bottom. It has a built-in graphics card. You can try by replacing the 330uf cap in the CPU core circuitry.
              Attached Files
              I'm not happy to be so strong. because it's not humanly

              Comment


                #8
                Re: Samsung NP365E5C random power off

                Originally posted by Sametbey View Post
                Your motherboard should be at the bottom. It has a built-in graphics card. You can try by replacing the 330uf cap in the CPU core circuitry.
                There are a bunch of 330uf capacitors in that circuit. If they were bad, wouldn't I see voltage spikes with an oscilloscope? I see a perfectly flat line in CPU core voltage. Could they still be to blame? Any way of testing without swapping all of them?

                Comment


                  #9
                  Re: Samsung NP365E5C random power off

                  It may be a wavy (distorted) waveform as shown in the picture. sometimes the capacitor may not support the inrush current draw. VCORE capacitors should be next to the processor.
                  I'm not happy to be so strong. because it's not humanly

                  Comment


                    #10
                    Re: Samsung NP365E5C random power off

                    this picture
                    Attached Files
                    I'm not happy to be so strong. because it's not humanly

                    Comment


                      #11
                      Re: Samsung NP365E5C random power off

                      Originally posted by Sametbey View Post
                      It may be a wavy (distorted) waveform as shown in the picture. sometimes the capacitor may not support the inrush current draw. VCORE capacitors should be next to the processor.
                      Thanks for the reply. I finally got some extra time today, I swapped out all of the 330uf capacitors under the cpu, a total of 5, I went ahead and swapped all just to be sure. But the laptop still randomly shuts off.

                      Comment


                        #12
                        Re: Samsung NP365E5C random power off

                        Fixed! Finally! I have found the component that was causing the issue. I'm going to let you guys know what it was just in case anyone stumbles upon this same issue in the future.

                        First off, this would have been a super easy fix IF the computer would have shut off and stayed off, but since I could always power it right back on, it made it a lot more difficult. I was able to find it because one day I decided to do a memory diagnostic, but leave it running indefinitely until it failed. That day it did not fail and I left it on by accident. The next morning, it would not turn on, it would light the power led for 5 seconds then turn off, without any fans or anything, until I unplugged it for awhile and plugged it back in (this was the first time it wouldn't let me turn it on). So I decided to do the exact same thing, so that it would fail in the same way, to check all the power up sequence voltages.

                        After going backwards from a missing "susp" voltage drop to activate all voltages, I found that the "FCH_PWR_EN" voltage was being sent from the smc, but the "FCH_PWR_EN#" never got low like it should. There is a double transistor that does this, when it receives the FCH_PWR_EN from the smc, it will drop the FCH_PWR_EN# line to low. This wasn't happening. The transistor was getting the signal, but not sending the # line to ground. The transistor that does this is Q25 (Q25a).

                        Funny, this transistor was right underneath the cpu socket so maybe it did start failing due to heat, and that's why at first I could use it for a lot longer when using an external fan. But anyway, now it just kept getting worse. After replacing this with a similar component (same voltage and amp tolerance) the computer hasn't powered off once after two days of continuous usage.

                        Seems silly it was this easy in the end, but I don't know how I could have found this failing component while always being able to power on. It's like it would fail instantaneously, and right after failing be back to normal.
                        Last edited by liquidzorch; 04-03-2021, 11:51 AM.

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