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Anyone know how the slug 5V to 3.3V power conversion works?

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  • Rod Whitby
    I have a slug which is not working (symptom is a short blink on the power led on power-up, and then nothing on any leds after that, and nothing on the serial
    Message 1 of 9 , Nov 1, 2007
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      I have a slug which is not working (symptom is a short blink on the
      power led on power-up, and then nothing on any leds after that, and
      nothing on the serial console), and I'm measuring less than 1V on the
      3.3V power rail.

      Does anyone have any details on the slug's internal power conversion
      circuitry? I'd like to work out what has failed ...

      -- Rod
    • Jon Pounder
      ... my first guess would be nothing :) if you have a low voltage like that and for sure there is sufficient input to the converter circuitry, in all likelyhood
      Message 2 of 9 , Nov 1, 2007
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        Quoting Rod Whitby <rod@...>:

        > I have a slug which is not working (symptom is a short blink on the
        > power led on power-up, and then nothing on any leds after that, and
        > nothing on the serial console), and I'm measuring less than 1V on the
        > 3.3V power rail.
        >
        > Does anyone have any details on the slug's internal power conversion
        > circuitry? I'd like to work out what has failed ...


        my first guess would be nothing :) if you have a low voltage like that
        and for sure there is sufficient input to the converter circuitry, in
        all likelyhood its overloaded and just gone into some reduced voltage
        mode to save itself from burning out (even the cheapest LM78xx
        regulators do that).

        I'd spend the time looking for a short someplace. (if nothing turns up
        visually use the old cut and conquer technique where you just start
        cutting traces past the regulator circuit till you get a branch back
        to the right voltage, then start soldering back and cutting more
        places till you narrow down to the short.

        just make notes of what you cut so you can put it all back.

        >
        > -- Rod
        >
        >
        >
        > Yahoo! Groups Links
        >
        >
        >
        >



        Jon Pounder

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      • michael taylor
        ... Where are you measuring that power rail? What is the wall-wart power supply voltage unloaded (not plugged into the board) and loaded (plugged into the
        Message 3 of 9 , Nov 1, 2007
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          On 11/1/07, Rod Whitby <rod@...> wrote:
          > I have a slug which is not working (symptom is a short blink on the
          > power led on power-up, and then nothing on any leds after that, and
          > nothing on the serial console), and I'm measuring less than 1V on the
          > 3.3V power rail.

          Where are you measuring that power rail?

          What is the wall-wart power supply voltage unloaded (not plugged into
          the board) and loaded (plugged into the board, measure from the power
          plug on board is easiest)?

          Some quick measurements I just did.

          Wall wart,
          unloaded: 5.12 V
          loaded: 5.08 V

          C45: 5.08V (near RAM)
          C21: 3.3V (near Realtek Ethernet chip)
          C146: 3.xx V (underside, near power switch)
          D13: 3.0V (anode) 2.4 (or 2.5)V (cathode) (underside near 4 LEDs and
          Real-Time-Clock)


          > Does anyone have any details on the slug's internal power conversion
          > circuitry? I'd like to work out what has failed ...

          I assume you have identified U16 as the power management IC, Feeling
          Technology's FP5452
          with under-voltage lock out, and short circuit protection.

          FP5452 datasheet <http://www.dianyuan.com/bbs/u/46/1160442105.pdf>

          Don't know if that helps at all.
        • MIKi
          An step-down voltage regulator should have a coil, a big capacitor and a small black integrated circuit. As I see the picture on the main page here, the
          Message 4 of 9 , Nov 1, 2007
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            An " step-down " voltage regulator should have a coil, a big capacitor
            and a small black integrated circuit.
            As I see the picture on the main page here, the slug should have two
            regulator. The first is left from the memory-s, the second is on the
            bottom close to the right corner.
          • Rod Whitby
            ... Any chance you could draw the circuit diagram for me (and explain it s operation), so I can match it to the components on the slug and start measuring some
            Message 5 of 9 , Nov 1, 2007
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              MIKi wrote:
              > An " step-down " voltage regulator should have a coil, a big capacitor
              > and a small black integrated circuit.
              > As I see the picture on the main page here, the slug should have two
              > regulator. The first is left from the memory-s, the second is on the
              > bottom close to the right corner.

              Any chance you could draw the circuit diagram for me (and explain it's
              operation), so I can match it to the components on the slug and start
              measuring some voltages?

              Hi-res photos of the PCB (including boards will all components removed)
              can be found at:

              http://www.nslu2-linux.org/gallery/nslu2_pcbs

              -- Rod
            • MIKi
              ... This circuits are very simples, at home visual inspection usable only. Because of the converters working on higher frequencies, You cant measure or check
              Message 6 of 9 , Nov 1, 2007
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                > Any chance you could draw the circuit diagram for me (and explain it's
                > operation), so I can match it to the components on the slug and start
                > measuring some voltages?
                >

                This circuits are very simples, at home visual inspection usable only.
                Because of the converters working on higher frequencies, You cant
                measure or check anything on your desk : (
              • MIKi
                Perhaps this values should be OK, but as You see w/o more information nobody can say anything about your voltages ... : (
                Message 7 of 9 , Nov 2, 2007
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                  Perhaps this values should be OK, but as You see w/o more information
                  nobody can say anything about your voltages ... : (
                • Phil Endecott
                  ... Hi Rod, I know exactly how it works. Do you have access to an oscilloscope? Phil. (If you cc: me in your reply, I ll see it sooner; I m subscribed to the
                  Message 8 of 9 , Nov 2, 2007
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                    Rod Whitby wrote:
                    > I have a slug which is not working (symptom is a short blink on the
                    > power led on power-up, and then nothing on any leds after that, and
                    > nothing on the serial console), and I'm measuring less than 1V on the
                    > 3.3V power rail.
                    >
                    > Does anyone have any details on the slug's internal power conversion
                    > circuitry? I'd like to work out what has failed ...


                    Hi Rod,

                    I know exactly how it works. Do you have access to an oscilloscope?


                    Phil.

                    (If you cc: me in your reply, I'll see it sooner; I'm subscribed to the digest.)
                  • sdm485
                    The FP5452 datasheet has an application note that should provide the basic design. I just took a look at one of my units and capacitor C45 is bulging in the
                    Message 9 of 9 , Nov 2, 2007
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                      The FP5452 datasheet has an application note that should provide the
                      basic design. I just took a look at one of my units and capacitor C45
                      is bulging in the same way as ones on a few failed motherboards I
                      fixed a while ago. It is possible that you have the same problem.
                      There was quite a scandal about it a few years back. If it turns out
                      to be a problem, you need a low ESR device in that location and
                      replacing C48 as well would be a good idea.

                      Steve



                      --- In nslu2-linux@yahoogroups.com, Rod Whitby <rod@...> wrote:
                      >
                      > I have a slug which is not working (symptom is a short blink on the
                      > power led on power-up, and then nothing on any leds after that, and
                      > nothing on the serial console), and I'm measuring less than 1V on the
                      > 3.3V power rail.
                      >
                      > Does anyone have any details on the slug's internal power conversion
                      > circuitry? I'd like to work out what has failed ...
                      >
                      > -- Rod
                      >
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