Quick 3842 troubleshooting

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  • Th3_uN1Qu3
    Believe in
    • Jul 2010
    • 6031
    • Romania
    #1

    Quick 3842 troubleshooting

    Just fixed the 5vsb of a Spire 600W PSU (decent construction, but really crappy caps everywhere, considering a full recap but will have to ask the owner first). It was made with a 3842 and i thought i'd share how i fixed it.

    Output caps were both bloated, replaced. No go. Switching MOSFET tested fine. I found the startup cap bad too. Not bloated, just dry. No capacitance. Replaced and Vcc still sat at 8.9v and the controller did not start up, no output, no Vref. Checked startup resistor - measured at 150kOhm which is exactly what the color code said. Checked all pins of the 3842 for shorts to GND or Vcc - nothing.

    Then i decided to measure the current consumption. So i lifted one end of the startup resistor and set my meter to mA. It read 3.7mA. The datasheet says that 1mA is enough to start the reference regulator. So i replaced the 3842 and hey presto, 5vsb is up.

    The rest, i'm leaving for tomorrow. The owner had already replaced a few caps, i pulled both heatsinks and replaced the remaining bloated caps in the secondary. I'll swap out some of the small caps too before i put the heatsinks back on.

    PS. Add Jenpo to the bad caps list. Even the primaries were bad, and this PSU doesn't even have dust in it, it's almost brand new. It does have APFC tho.
    Originally posted by PeteS in CA
    Remember that by the time consequences of a short-sighted decision are experienced, the idiot who made the bad decision may have already been promoted or moved on to a better job at another company.
    A working TV? How boring!
    Tags: None
    • tom66
      EVs Rule
      • Apr 2011
      • 32560
      • UK
      #2
      Re: Quick 3842 troubleshooting

      3.7mA across 150k is ~550V; so no wonder it didn't start. Odd failure there... it must have become leaky. Might have worked in the early stages on high line voltage or at certain temperatures.

      I still remain skeptical that APFC cooks caps. In many cases the ripple current should be lower. The difference is it's at a higher frequency, so general purpose primaries are a no go - something like Hitachi-AIC HV caps are good, and they're relatively cheap.
      Please do not PM me with questions! Questions via PM will not be answered. Post on the forums instead!
      For service manual, schematic, boardview (board view), datasheet, cad - use our search.

        Comment

        • Th3_uN1Qu3
          Believe in
          • Jul 2010
          • 6031
          • Romania
          #3
          Re: Quick 3842 troubleshooting

          The resistor dropped exactly 357.3v at that 3.7mA. PFC voltage is 367v. As for the caps, they were just crap, finding a bunch of bloaters (and some that failed without bloating) in an almost new PSU clearly says something about their quality.

          The PSU is very interesting, i'll post some pics in the build quality pictorial. It uses half bridge topology with BJTs, classic circuit with TL494 and LM339, they just added an APFC stage before it. However, it does look like it has enough beef for 600W - the transformer and inductor are large, the rectifiers are overspec'd by a healthy amount, and there's a 120mm fan on the bottom, as well as a 80mm on the exhaust. The soldering is crap tho. I think it is Sirfa who made it.
          Originally posted by PeteS in CA
          Remember that by the time consequences of a short-sighted decision are experienced, the idiot who made the bad decision may have already been promoted or moved on to a better job at another company.
          A working TV? How boring!

            Comment

            • tom66
              EVs Rule
              • Apr 2011
              • 32560
              • UK
              #4
              Re: Quick 3842 troubleshooting

              I have a 500W power supply with active PFC which uses the same half bridge topology. Mine is stuffed with crappy Teapo everywhere, primary and secondary.
              Please do not PM me with questions! Questions via PM will not be answered. Post on the forums instead!
              For service manual, schematic, boardview (board view), datasheet, cad - use our search.

                Comment

                • Th3_uN1Qu3
                  Believe in
                  • Jul 2010
                  • 6031
                  • Romania
                  #5
                  Re: Quick 3842 troubleshooting

                  The OEM is actually Topower - it's got TOP written on all the transformers, and there's also TOP-600P5 written in tiny text on the label. I'll put up pictures shortly.

                  I guess Spire asked them to use cheap caps - it's the same platform as used here, and i don't think Hipro would accept to use such low quality capacitors. Spire blew all their budget on those fancy cables...
                  Originally posted by PeteS in CA
                  Remember that by the time consequences of a short-sighted decision are experienced, the idiot who made the bad decision may have already been promoted or moved on to a better job at another company.
                  A working TV? How boring!

                    Comment

                    • tom66
                      EVs Rule
                      • Apr 2011
                      • 32560
                      • UK
                      #6
                      Re: Quick 3842 troubleshooting

                      Originally posted by Th3_uN1Qu3
                      The OEM is actually Topower - it's got TOP written on all the transformers, and there's also TOP-600P5 written in tiny text on the label. I'll put up pictures shortly.

                      I guess Spire asked them to use cheap caps - it's the same platform as used here, and i don't think Hipro would accept to use such low quality capacitors. Spire blew all their budget on those fancy cables...
                      Mine is a HIPER. Maybe a pretend "Hipro". If/when I recap it I'll try to figure out the OEM.
                      Last edited by tom66; 10-05-2012, 03:19 PM.
                      Please do not PM me with questions! Questions via PM will not be answered. Post on the forums instead!
                      For service manual, schematic, boardview (board view), datasheet, cad - use our search.

                        Comment

                        • Pentium4
                          CapXon Be Gone
                          • Sep 2011
                          • 3741
                          • USA
                          #7
                          Re: Quick 3842 troubleshooting

                          Originally posted by Th3_uN1Qu3
                          The OEM is actually Topower - it's got TOP written on all the transformers, and there's also TOP-600P5 written in tiny text on the label. I'll put up pictures shortly.

                          I guess Spire asked them to use cheap caps - it's the same platform as used here, and i don't think Hipro would accept to use such low quality capacitors. Spire blew all their budget on those fancy cables...
                          Do you still have these pictures to upload?
                          Originally posted by tom66
                          Mine is a HIPER. Maybe a pretend "Hipro". If/when I recap it I'll try to figure out the OEM.
                          It's probably Andyson. I have a Hiper unit with some bloated Teapo, and it's made by Andyson

                            Comment

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