Fsp300-60pn(pf)

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  • pdavid
    Badcaps Veteran
    • Jan 2011
    • 279
    • Hungary
    #1

    Fsp300-60pn(pf)

    I had a psu like this only it was the 250W model with a separte 12V DC output. The pcb is the same anyway.

    Seemed to be a simple standby problem at first... just replace two bad caps and done.
    But the psu has more serious problems. The standby voltage is pulsing between 2-4 Volts, even some ac voltage is present. Same for the pson signal. Maybe the controller is bad, but I suspect that the feedback is not working and I have to point out the faulty component. It's hard to diagnose this without a scope, but since the the backlight died on my 5 month old Voltcraft I have to wait until it gets "repaired".

    So, I'm going to check the primary and secondary side for bad parts in the standby and feedback path. I be glad if it would be just some small resistor, diode or cap and not some active components.
    Tags: None
    • pdavid
      Badcaps Veteran
      • Jan 2011
      • 279
      • Hungary
      #2
      Re: Fsp300-60pn(pf)

      I checked everything in the standby and feedback, trafos too and eventually I striped down the whole primary just too look around I replaced all small caps in the primary and on the controll board. Two small 2.2uF 50V caps were 1.4-1.8uF. Haven't made any measurements on the KA3511 yet. Tomorrow I'll put everything back together and try to revive this thing...

      Does someone know what is the component on the B1 position? It doesn't seem like some supressor or fuse. On my meter it reads open. It just makes a bridge from before and after the neutral's EMI filter section.
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        • pdavid
          Badcaps Veteran
          • Jan 2011
          • 279
          • Hungary
          #3
          Re: Fsp300-60pn(pf)

          I removed the feedback trafo and compared it with a same type and known good one. I noticed that on it's primary side the winding which goes to an opto reads 0,8 Ohms and on the "working" one this value is 0,2. I haven't found any failed components around here so I'm going to swap the transformer and see what happens.
          Hopefully I'll get my scope back next tuesday.
          Attached Files

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            • pdavid
              Badcaps Veteran
              • Jan 2011
              • 279
              • Hungary
              #4
              Re: Fsp300-60pn(pf)

              It turns out that the resistor on R1 had loose soldering, but most importantly the green film capacitor next to the standby trafo was shorted! All the trafos were good after all...

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