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Why does PCH get shorted internally?

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    Why does PCH get shorted internally?

    Dear members.

    I have faced many times various laptops that have PCH with an internal short to GND on the 3.3v rail. I have seen this kind of short both in old and recent laptops.
    Once I faced this kind of short, I observed that the other components on the mainboard were fine. For example, the 5v and the 3.3v rails were present. Resistance on the 3.3v was low (about 4 ohms) but not zero.
    Another time I faced this kind of short, I observed that the 3.3v rails was not present due to the short.
    Another example was described in the following page:
    https://www.badcaps.net/forum/showthread.php?t=105356


    What do cause this kind of short to happen inside PCH?

    Thanks
    Last edited by caspian; 05-12-2022, 05:13 AM.

    #2
    Re: Why does PCH get shorted internally?

    I have also noticed the same..the most common is internal short...sometimes they even partially work..sometimes not....resistance arround 2,8 ohm on 3.3v rails.
    I am not 100% sure...but i believe it is because of long time heating. The reason i believe its heating is ...first, it is more common fault in smaller 15,6 inch laptops then bigger 17,3...Also i have noticed that laptops that use passive cooler on pch last longer and dont have that much problems with pch...like asus g752 series....
    I can not be sure..but that is what i found.
    Last edited by myth77; 05-12-2022, 05:43 AM.

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      #3
      Re: Why does PCH get shorted internally?

      We've found that several blown PCHs were caused by, apparently, external audio equipment--i.e. DJ's/music producers, etc. We have confirmed at least 5 cases the past ~6-7 years where a surge through the audio circuitry reached the PCH, blowing it. On several occasions, the user reported the laptop failed "while they were using it" (for work/music, etc). Only one time did the laptop fail when not in use, and customer reported a thunderstorm while he had external speakers connected to the laptop...so a bit more support there.

      I have not dug any deeper than this, but figured I'd mention it.
      Last edited by ugamazing; 05-18-2022, 06:14 AM.

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        #4
        Re: Why does PCH get shorted internally?

        Indeed it does happen (and more commonly blown audio circuit) because sometimes with some combination of cables and adapters, they end up plugging phantom power into the laptop. Still it's very rare so all the other failures are unrelated to this. Of course bad USB devices can also damage the PCH, but most of the times there's not really an external factor at play for these 8-series and newer PCH to die.
        OpenBoardView — https://github.com/OpenBoardView/OpenBoardView

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          #5
          Re: Why does PCH get shorted internally?

          Originally posted by piernov View Post
          Indeed it does happen (and more commonly blown audio circuit) because sometimes with some combination of cables and adapters, they end up plugging phantom power into the laptop. Still it's very rare so all the other failures are unrelated to this. Of course bad USB devices can also damage the PCH, but most of the times there's not really an external factor at play for these 8-series and newer PCH to die.
          Thanks, Piernov!

          P.S. A while back, you purchased some as-is/for-repair logic boards from us; if you remember me, shoot me another email if you want/need anymore boards--we have hundreds we're getting rid of.

          Comment


            #6
            Re: Why does PCH get shorted internally?

            hdmi, audio, usb. litterally anything that u plug in computer can kill PCH

            Comment


              #7
              Re: Why does PCH get shorted internally?

              From 8th gen onwards, i beleive its designed to fail by INTEL.

              Comment


                #8
                Re: Why does PCH get shorted internally?

                I've replaced today one 8th gen PCH on Tongfang laptop, I believe it was shorted when dude I bought it from plugged LCD cable while battery was installed. However, I had 0.5ohms on 3.3V coil and 0.2 ohms on 1.05V, now all resistances are good but laptop is not powering on, just power LED lights up for 2 seconds or so. I don't see anything shorted.

                I replaced PCH a few weeks ago on Clevo N850EP6 and also I got power light for few seconds and that's it.

                My question is next:

                - What's the best procedure for replacing PCH or CPU?
                - Does ME section of BIOS has to be cleaned?
                - Is it possible to use CPU/PCH from donor board?

                I read something about bootguard, chain of thrust and such stuff, fuse resistors, one time write memory etc,...

                Can someone point me in right direction because I obviously don't know what I'm doing? :=)

                Thank you in advance!

                Comment


                  #9
                  Re: Why does PCH get shorted internally?

                  CPU/PCH are only made for 24 months tops for each generation. Most of the ones you see available online are pulled from old boards. Who knows if they work or not. If they don't, the vendor will blame your installation for it not working. This is why most people don't bother replacing these components and the boards are used as donors. Not to mention the temperature profiling for BGA rework can vary from board to board. Is it worth the effort really vs replacing the board?

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                    #10
                    Re: Why does PCH get shorted internally?

                    @balkanboy, You need to make sure the cpuid is supported in bios. Clean me bios is a must after pch replacement. However, agree with #reformatt's views completely unless and otherwise its a mainboard which is either very expensive or not available in market. I replace SOC only in highend boards and/or boards which are not available at all and customer is willing to spend $100 or more.

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                      #11
                      Re: Why does PCH get shorted internally?

                      So what would happen if you don't clean me after PCH replacement, no boot at all like I'm experiencing or something else?

                      Also does it have to be cleaned before replacing PCH or it could be done after as well? I think I read somewhere a long time ago that new PCH gets burned some microcode on initial startup, and if you haven't cleaned it before you can buy new PCH and throw the other in garbage. Also it said that used PCHs can't be used. Don't know if it's true or not. Maybe it's not same with every laptop brand.

                      I'm interested in those stuff as I got lot of gaming laptops I couldn't fix I just stashed away, with bad CPUs, GPUs or PCHs but I'm still practicing as reballing is the pain in the ass. Don't want to start real repairs when I don't know 100% what am I doing. Cheapest boards for such laptops are $400+ and I bought them over the years so I got to try something

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                        #12
                        Re: Why does PCH get shorted internally?

                        You need to clean ME region when replacing PCH, yes.

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                          #13
                          Re: Why does PCH get shorted internally?

                          Cleaning the me region is important-it doesnt matter whether you flash the clean me bios before or after pch replacement. The main point is mb should have cleaned me bios before turning on after pch replacement. Sometimes you will get display after pch replacement even with old bios but with SOC mb, you will not get display unless you clean the me region after replacement.

                          Comment


                            #14
                            Re: Why does PCH get shorted internally?

                            So if I haven't cleaned ME and I tried to power it ON does that mean PCH is wasted or I can still clean it?
                            I just got power LED for 2 seconds, very first time I powered it on after replacement I had same LED pattern, wasn't any different.

                            Comment


                              #15
                              Re: Why does PCH get shorted internally?

                              No, PCH wont get damaged with old bios. You can flash clean me bios now and check again.

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