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PC8044 from HP desktop, exploded ceramics, blasted single FET

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    PC8044 from HP desktop, exploded ceramics, blasted single FET

    Found this dead unit in an HP 6000 series desktop with first generation i3 CPU. Could not identify the manfucaturer, it is a TFX unit with UL of E314577. Being filled with Ltec and AiShi(t), who knows. I first thought it will be just the secondary caps, but the problem is worse than that.

    Not sure if the unit overheated first which baked the CM6800 cap (47uF nominal, measures 52 uF and 65 ohm ) and made the single-forward FET explode, taking some ceramics with, or the other way around. Anyways, the Toshiba 2SK3878 is blasted drain to source. There are also two small THT ceramics in parallel, between the drain (and transformer center pin) and the HV input (+390 V). I can not get their values as one of them vaporised and the other is broken. Any idea? I'd guess it to be 1 or 2 kV and some very small value. I managed to desolder the second one which has the ceramic disc broken, but it seems the electrode is still attached to the actual capacitor core, which measures slightly under 1 nF. I guess this is beliavable.

    So would it be safe to use two 1nF or single 2.2nF cap? I hope changing the capacitance by a tiny bit should not move the circuit balance too much. Cause if I am not mistaken, these caps are quite important as they transfer some power at the switched frequency which is 52-74 kHz for CM6800.
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    #2
    Re: PC8044 from HP desktop, exploded ceramics, blasted single FET

    I realized that I have second, still working desktop with the same unit. Looking at how this one ended, I'll crack that one open too, replace the caps and check the values of those two ceramics while in there
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      #3
      Re: PC8044 from HP desktop, exploded ceramics, blasted single FET

      photo's ???

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        #4
        Re: PC8044 from HP desktop, exploded ceramics, blasted single FET

        You know how it's with me and taking photos! Like you're here the first time
        Less jewellery, more gold into electrotech industry! Half of the computer problems is caused by bad contacts

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          #5
          Re: PC8044 from HP desktop, exploded ceramics, blasted single FET

          it sounds similar to the older psu's i'v mentioned where an under-rated ceramic snubber cap fails and blows the fet, driver and a shitload of other stuff.

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            #6
            Re: PC8044 from HP desktop, exploded ceramics, blasted single FET

            It was overheating though. The controller board with CM6800 is all brown, also around the FET the main board is darkened which spreaded also around solder taps for the heatsink. Think I'll add some conductive silicone rubber between the heatsink and the casing, if I manage to make it working again.
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              #7
              Re: PC8044 from HP desktop, exploded ceramics, blasted single FET

              that stuff is not great,
              i'f you go that route then try to shim it with a sheet or block of ally.

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                #8
                Re: PC8044 from HP desktop, exploded ceramics, blasted single FET

                Wut? I have only good experience with that. Granted, it sometimes tends to leak silicone oil when heated.
                Less jewellery, more gold into electrotech industry! Half of the computer problems is caused by bad contacts

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                  #9
                  Re: PC8044 from HP desktop, exploded ceramics, blasted single FET

                  it's conductivity may be o.k. but it's not a substitute for metal - it's for gluing heatsinks to stuff.

                  use it to bond a metal block.

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                    #10
                    Re: PC8044 from HP desktop, exploded ceramics, blasted single FET

                    Would not put anything metal there for several reasons. This thing works great. It's not only for heatsinks, at least not the thickness I use (3 and 5 mm or combination of both). On the contrary, it's for transfering heat from almost anything, no matter the shape, to somewhere else, being electrically insulated. In this case, thick heatsink to metal casing. Good for removing heat from solder side of a board or things like transformers too.
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                      #11
                      Re: PC8044 from HP desktop, exploded ceramics, blasted single FET

                      What a piece of chinese shit this is?! It was a miracle the second unit was still working as both the caps were already cracking and both were turned into pretty much a bit of sand when I tried to remove them. All that after removing the whole heatsink anyway because of lack of space.

                      I managed to measure one at some 936 pF too so I guess some generic 1nF/2kV or 2.2nF/2kV caps should work?

                      The Aishi(t) WH 47/25 onthe CM6800 board was also screwed already too at 15 ohm ESR…
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                        #12
                        Re: PC8044 from HP desktop, exploded ceramics, blasted single FET

                        Found some blue-disc ceramics, 2.2 nF/2 kV, used as Y before but without safety margins, I guess I can use this, no?
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                          #13
                          Re: PC8044 from HP desktop, exploded ceramics, blasted single FET

                          LOL
                          atleast their designs are consistant!

                          so you cant read any print on them??

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                            #14
                            Re: PC8044 from HP desktop, exploded ceramics, blasted single FET

                            https://www.badcaps.net/forum/showthread.php?t=50864

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                              #15
                              Re: PC8044 from HP desktop, exploded ceramics, blasted single FET

                              Don't see anything. Either there was no print at all, or it disappeared later.

                              Think this could be more common problem. Just checked some old Enermax unit which I unsucessfully tried to repair some time ago and used parts to save other unit later to see whether there are some ceramics I could use. Guess what, one was also blasted
                              Last edited by Behemot; 10-16-2018, 08:38 AM.
                              Less jewellery, more gold into electrotech industry! Half of the computer problems is caused by bad contacts

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                                #16
                                Re: PC8044 from HP desktop, exploded ceramics, blasted single FET

                                badcaps needs to be renamed badcaps(inc ceramics)

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