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Replacement Rifa caps for Astec PSU

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    Replacement Rifa caps for Astec PSU

    Hi,

    I'm refurbishing an old Astec PSU, model 042 02017504, from an LSI Octopus computer circa 1985. I've sourced replacements for the Rifa X rated caps, but have the following Rifa caps that I'm unsure of the best replacements. Can anyone help, please?

    The first has the following markings
    2200pf
    PME 277 MB 422
    40/085/21
    GPT
    CRD
    250v-MP
    VDE REG NR 5201.212222

    The second has the following markings:
    0,68uf +-10%
    PHE 280
    DB 668
    100V=
    40/100/56

    Attached are pictures from the top, front and back of each cap. Advice on the most suitable replacements would be appreciated.

    Thanks,
    Steve
    Attached Files

    #2
    Re: Replacement Rifa caps for Astec PSU

    If it's of any help, here's a pic of the PSU:
    Attached Files

    Comment


      #3
      Re: Replacement Rifa caps for Astec PSU

      The 2200pF VDE unit is a Y-class (safety) unit, and the 0.68uF unit can be replaced with a polyester unit.
      In addition, I recommend replacing the other 2200pF VDE unit (near C4) along with C37 and C39 with polyester units.

      Clear epoxy coated Rifa/Miniprint capacitors are unreliable from what I can see.
      My first choice in quality Japanese electrolytics is Nippon Chemi-Con, which has been in business since 1931... the quality of electronics is dependent on the quality of the electrolytics.

      Comment


        #4
        Re: Replacement Rifa caps for Astec PSU

        I forgot to say that the 0.22uF X unit should also be replaced (X-class, safety type).
        My first choice in quality Japanese electrolytics is Nippon Chemi-Con, which has been in business since 1931... the quality of electronics is dependent on the quality of the electrolytics.

        Comment


          #5
          Re: Replacement Rifa caps for Astec PSU

          The RIFA epoxy moulded ones seem to crack over time, apparently soak up moisture from the environment, short out, and catch fire.

          Lots of threads about them across many electronics forums.
          "Tantalum for the brave, Solid Aluminium for the wise, Wet Electrolytic for the adventurous"
          -David VanHorn

          Comment


            #6
            Re: Replacement Rifa caps for Astec PSU

            Safety capacitors do fail over (a long) time, and I don't think impregnated paper is especially inferior to polyester or polypropylene. It's an accumulated damage mechanism.

            So if you're hoping the P/S will be in use another 30+ years from now, there's a reasonable chance whatever you used for X and Y capacitors will need replacing.

            As for that 100V PHE280 series part, I'd find a polyester part so as to match the characteristics and go for the same lead spacing. It may have been chosen because polyester film caps are relatively inexpensive, but whether for characteristics or price, it's all good.
            PeteS in CA

            Power Supplies should be boring: No loud noises, no bright flashes, and no bad smells.
            ****************************
            To kill personal responsibility, initiative or success, punish it by taxing it. To encourage irresponsibility, improvidence, dependence and failure, reward it by subsidizing it.
            ****************************

            Comment


              #7
              Re: Replacement Rifa caps for Astec PSU

              Originally posted by japlytic View Post
              The 2200pF VDE unit is a Y-class (safety) unit, and the 0.68uF unit can be replaced with a polyester unit...
              Originally posted by japlytic View Post
              ...the 0.22uF X unit should also be replaced (X-class, safety type).
              Thanks japlytic,

              I'd guessed that the 2200pF may have been a Y-class, and my next step this morning would have been (in fact still is to double check) to inspect the traces to see if it's between neutral and ground. Good to know the 0.68uF can be replaced with a polyester equivalent cap.

              I've already replaced the 0.22uF with an X-class equivalent - the pic was taken just after I'd removed two of the questionable caps in order to get the full details.

              Final step is to print and attach labels to the PSU outer casing detailing the caps that have been replaced.

              Cheers

              Comment


                #8
                Re: Replacement Rifa caps for Astec PSU

                Originally posted by PeteS in CA View Post
                ...So if you're hoping the P/S will be in use another 30+ years from now, there's a reasonable chance whatever you used for X and Y capacitors will need replacing.
                I suspect in another 30+ years, this P/S will be someone elses problem or probably in landfill should my kids not want "dad's old computer junk". lol

                Comment


                  #9
                  Re: Replacement Rifa caps for Astec PSU

                  Originally posted by Agent24 View Post
                  The RIFA epoxy moulded ones seem to crack over time, apparently soak up moisture from the environment, short out, and catch fire.

                  Lots of threads about them across many electronics forums.
                  That's been my experience with the few PSUs I've repaired so far, the cracking, not the catching fire - I usually inspect and replace those caps before testing the PSU. However, I was struggling to find data sheets for the caps I'd mentioned.
                  Last edited by Osmosis; 02-10-2018, 04:54 AM.

                  Comment


                    #10
                    Re: Replacement Rifa caps for Astec PSU

                    Looks like Kemet (the current owner of Evox-Rifa) doesn't do the PME 277 series, http://www.kemet.com/FEBG%20-%20AC%2...I%20Capacitors

                    Don't see a PHE 280 series, either, http://www.kemet.com/FEBG_general_pu...ilm_capacitors
                    PeteS in CA

                    Power Supplies should be boring: No loud noises, no bright flashes, and no bad smells.
                    ****************************
                    To kill personal responsibility, initiative or success, punish it by taxing it. To encourage irresponsibility, improvidence, dependence and failure, reward it by subsidizing it.
                    ****************************

                    Comment

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