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9v super basic wall wart issue

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    9v super basic wall wart issue

    This is one of those worthless and time wasting repairs but it's bugging me and I want to figure it out. Simple 9v 1a SMPS wall wart and it's bouncing between 8.2 and 9.4v without load. I've pulled out every single cap and all tested fine. I've replaced the opto and same exact issue. All diodes are testing fine. I'm not sure if the IC can cause this or if the IC had issues you wouldn't get anything at all on output.
    Attached Files
    --------------------------------------------------------------
    Ryzen 3600x
    16GB Patriot 3600MHz
    MSI B450 Gaming Plus
    MSI Air Boost Vega 56
    Acer 32" 1440P Freesync
    Rosewill Capstone 750W
    --------------------------------------------------------------
    Hakko FX-888D Station
    FX-8802 Iron
    MG Chem .8mm 63/37 RA 2.2%

    #2
    Re: 9v super basic wall wart issue

    power supplies tend to have minimum load, does it surge with some load?

    Comment


      #3
      Re: 9v super basic wall wart issue

      I'll check later tonight
      --------------------------------------------------------------
      Ryzen 3600x
      16GB Patriot 3600MHz
      MSI B450 Gaming Plus
      MSI Air Boost Vega 56
      Acer 32" 1440P Freesync
      Rosewill Capstone 750W
      --------------------------------------------------------------
      Hakko FX-888D Station
      FX-8802 Iron
      MG Chem .8mm 63/37 RA 2.2%

      Comment


        #4
        Re: 9v super basic wall wart issue

        Replace that small electrolytic C3

        Comment


          #5
          Re: 9v super basic wall wart issue

          Look if C3 has something to with the feedback and change it.

          Comment


            #6
            Re: 9v super basic wall wart issue

            I wonder if C3 might be the issue

            Comment


              #7
              Re: 9v super basic wall wart issue

              The 431 may be hunting.

              Try a 150-1k resistor across the IR LED in the opto.
              Points are marked in attached image.

              Change the small cap on pri side to 22u/50v or 47u/50v.
              Attached Files
              "pokemon go... to hell!"

              EOL it...
              Originally posted by shango066
              All style and no substance.
              Originally posted by smashstuff30
              guilty,guilty,guilty,guilty!
              guilty of being cheap-made!

              Comment


                #8
                Re: 9v super basic wall wart issue

                I pulled all caps one by one and they all checked out. I can replace it anyway but don't know what good it will do
                --------------------------------------------------------------
                Ryzen 3600x
                16GB Patriot 3600MHz
                MSI B450 Gaming Plus
                MSI Air Boost Vega 56
                Acer 32" 1440P Freesync
                Rosewill Capstone 750W
                --------------------------------------------------------------
                Hakko FX-888D Station
                FX-8802 Iron
                MG Chem .8mm 63/37 RA 2.2%

                Comment


                  #9
                  Re: 9v super basic wall wart issue

                  Originally posted by kaboom View Post
                  The 431 may be hunting.

                  Try a 150-1k resistor across the IR LED in the opto.
                  Points are marked in attached image.

                  Change the small cap on pri side to 22u/50v or 47u/50v.
                  9.21v stable. How do I know which one fixed it? Replacing C3 or adding a 330ohm resistor to the opto?

                  Ok, pulled the resistor off and it's still good. Pulled C3 which was a 10uf 50v cap and replaced with a Panasonic FC 47uf 50v.
                  Last edited by jayjr1105; 03-03-2022, 09:45 PM.
                  --------------------------------------------------------------
                  Ryzen 3600x
                  16GB Patriot 3600MHz
                  MSI B450 Gaming Plus
                  MSI Air Boost Vega 56
                  Acer 32" 1440P Freesync
                  Rosewill Capstone 750W
                  --------------------------------------------------------------
                  Hakko FX-888D Station
                  FX-8802 Iron
                  MG Chem .8mm 63/37 RA 2.2%

                  Comment


                    #10
                    Re: 9v super basic wall wart issue

                    Soldering heat from R&R'ing C3 may have temporarily "woken" it up.
                    The 431 seems to need a minimum load; when an unbypassed opto LED is the sole source of current to the 431, the latter can hunt.
                    Leading to voltage "bounce" at no load.

                    Perhaps it was C3.
                    With the original C3 in place, leave it out in the cold a while- it'll probably act up afterwards= cap(s) is/were suspect.

                    In similar SMPS wall warts, I've used 22-47u/50v caps, PW/HE/FC, for C3.
                    If a new C3 keeps it stable, even cold, you can probably leave the opto LED unbypassed.
                    "pokemon go... to hell!"

                    EOL it...
                    Originally posted by shango066
                    All style and no substance.
                    Originally posted by smashstuff30
                    guilty,guilty,guilty,guilty!
                    guilty of being cheap-made!

                    Comment


                      #11
                      Re: 9v super basic wall wart issue

                      Originally posted by kaboom View Post
                      Soldering heat from R&R'ing C3 may have temporarily "woken" it up.
                      The 431 seems to need a minimum load; when an unbypassed opto LED is the sole source of current to the 431, the latter can hunt.
                      Leading to voltage "bounce" at no load.

                      Perhaps it was C3.
                      With the original C3 in place, leave it out in the cold a while- it'll probably act up afterwards= cap(s) is/were suspect.

                      In similar SMPS wall warts, I've used 22-47u/50v caps, PW/HE/FC, for C3.
                      If a new C3 keeps it stable, even cold, you can probably leave the opto LED unbypassed.
                      The 431 is the small voltage reference SOT23 part?
                      --------------------------------------------------------------
                      Ryzen 3600x
                      16GB Patriot 3600MHz
                      MSI B450 Gaming Plus
                      MSI Air Boost Vega 56
                      Acer 32" 1440P Freesync
                      Rosewill Capstone 750W
                      --------------------------------------------------------------
                      Hakko FX-888D Station
                      FX-8802 Iron
                      MG Chem .8mm 63/37 RA 2.2%

                      Comment


                        #12
                        Re: 9v super basic wall wart issue

                        BTW, got home and still tested very stable around 9.2v.
                        --------------------------------------------------------------
                        Ryzen 3600x
                        16GB Patriot 3600MHz
                        MSI B450 Gaming Plus
                        MSI Air Boost Vega 56
                        Acer 32" 1440P Freesync
                        Rosewill Capstone 750W
                        --------------------------------------------------------------
                        Hakko FX-888D Station
                        FX-8802 Iron
                        MG Chem .8mm 63/37 RA 2.2%

                        Comment


                          #13
                          Re: 9v super basic wall wart issue

                          glad you got it fixed! I ran into a similar issue before on a different power supply where it only supplied half of the voltage.
                          Last edited by CapLeaker; 03-04-2022, 08:04 PM.

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