2xCH3041AHT PSUs problem

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  • ragis
    Senior Member
    • Mar 2013
    • 51
    • Bulgaria
    #1

    2xCH3041AHT PSUs problem

    Hi folks, i have a problem with two CH3041AHT PSUs they had bulged caps and i recaped them successfully.But now the first one starts after maybe 1min or so..
    The second one don't even starts...
    I measured them and on the first it has all the outputs like +5, -5, +24.
    The big cap 100uf/400v is 330V on both PSUs, but on the second not working the V is lost somewhere around the little filter cap 47uf/50V i measured it and it's 0V and on the other psu(the working one) is 14V
    The PWM IC is KA3842 and to go in to switch on mode it needs 16V.
    Thanks for your help, best regards
    ragis
    Attached Files
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    • budm
      Badcaps Legend
      • Feb 2010
      • 40746
      • USA
      #2
      Re: 2xCH3041AHT PSUs problem

      "But now the first one starts after maybe 1min or so" So did you replace that small startup/up running cap right next to the SMPS IC1 on this board?
      The dead board; What is the resistance reading between VCC pin 7 and GND pin 5?
      All 3 rectifier diodes on the cold side are all good?
      Attached Files
      Last edited by budm; 04-14-2017, 01:50 PM.
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        Comment

        • PeteS in CA
          Badcaps Legend
          • Aug 2005
          • 3581
          • USA, Unsure of Planet
          #3
          Re: 2xCH3041AHT PSUs problem

          Concur with budm. That is a flyback power supply. The controller is the KA3842 (Samsung or Fairchild). In all likelihood, the start-up bias for IC1 is provided by a high value resistor (e.g. R4 or R6) charging that cap, and once the circuit is running, a winding on the transformer provides bias. It may be that the start-up cap ESR is so high that it can't provide enough current to start the KA3842. If both are 2008-vintage, just replace the cap on both and see what happens.
          PeteS in CA

          Power Supplies should be boring: No loud noises, no bright flashes, and no bad smells.
          ****************************
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            Comment

            • ragis
              Senior Member
              • Mar 2013
              • 51
              • Bulgaria
              #4
              Re: 2xCH3041AHT PSUs problem

              Thanks guys for your reply i appreciate that,
              @budm: KA3842 the resistance between 7 pin (VCC) and 5 pin (GND) is 600R if i reverse the leads(red probe on 5pin and black probe on 7pin) if the leads are red to 7 pin and black to 5 pin i get 1 on my DMM or 0L for all( i test it on diode mode) this is the measurements for the working and not working psus( i think that they are ok)
              I didn't replaced the small cap, but i will maybe this week and i will post the results.
              For the 3 diodes on the cold side i tested them in diode mode and they all seem good on both psus.
              @PeteS in CA: R4 and R6 are good, i will replace the small cap and post the results.
              Thanks again, best regards
              ragis

                Comment

                • ragis
                  Senior Member
                  • Mar 2013
                  • 51
                  • Bulgaria
                  #5
                  Re: 2xCH3041AHT PSUs problem

                  Thanks, for the help !
                  As you suggested it was this little bastard 47uF/50V after replacing it on both everything works like charm !
                  Thanks again, best regards
                  ragis

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