PSU dm8000 no 3.3 V.

Discussion in 'Hardware troubles and Repair support.' started by nipon0007, Feb 17, 2017.

  1. nipon0007

    nipon0007 New Member

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    Hi Sir.
    I have checked the output volte of PSU the 3.31V output is 1.4V !! What is the problem this case?

    DM8000-power-supply-dcvoltage.jpg
     
  2. nipon0007

    nipon0007 New Member

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    Pin 4 & 10 of the power supply is output or input 3.31V??
    I saw the circuit is 3.31V is input from mainboard right?

    Dm8000hd-psu-switch.jpg
     
  3. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

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    Indeed, pin 4 is a input voltage to the power supply, this is to switch on the psu unit and is delivered from the motherboard which is lowered from the 14 vdc source.
    The switch voltages can also as you see on the drawing external be feed, but I do not recommend to do this when the power supply is connected to the motherboard.
    It's mainly to test the power supply without connected to the main board to see if it delivers the other voltages.
    Rest of the voltages are delivered from the power supply.

    If you want to test the power supply when it's still connected to the main board with a external switch voltage, then I recommend to disable the switch wire from the motherboard.
    However as I see it, it is useless, because the psu is switching on, so the switch voltage is sufficient to power on the psu.

    That both voltages collapse can be caused from the main board, but this is only to know if you are sure that the power supply is working well.
    The best and easy way is to test it with another power supply, if you have one, or test the power supply unballast (not connected to the main board) to see if the other voltage becomes normal.
     
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  4. nipon0007

    nipon0007 New Member

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    Thanks.
    The output voltage checked by without connect with mainboard.
    I think so the total 14 pin is output voltage but actually pin 4 is input voltage from the mainboard.
    I has repair&change capacitor, chip ic, diode it's back to fine but after used open 4-5 times is back to bad.
     
  5. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

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    The psu 3v delivery to the main board is a important voltage, lower than 3v may cause instability which could result that the motherboard sometimes just works, and sometimes failed.
    Best is to monitor the 3v psu output to see when it failed.

    Or test the psu external, without connected to the motherboard and ballast the 3v output to see if it collapse.
    Nevertheless I do not know the total amps consumption of the 3v main board circuit to know how much the psu 3v output should have.
    But it is possible that the amps of this psu 3v circuit has become weak, and may cause instability to the working of the motherboard.
     
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  6. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

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    I've taken the time to check this 3.3v about how much it consumes Amps and it's not so much as I thought.
    It's low Amps and it's mainly for the 300N03S Fast switching on the motherboard.
    So if it's is not caused due the power supply, then it could be the 300N03S, because if that fails it could lower the 3.3v delivery from the psu.

    In any case, a long time ago I had made this information picture for someone which had also a issue with this 3.3v voltage while it was not caused due the psu.
    Maybe it helps you also.

    Dm8000hd-T1208-300N3S.jpg

    This 300N03S mosfet ic you can also find on a dm tuner module, so if you want to replace it you can take it from a tuner spare part board if you have one.
     
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  7. nipon0007

    nipon0007 New Member

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    Many Thanks.
    The DM8000 is back to fine work now. I do not yet to replace anythink now.When it's Bad the All voltage is swing.
     
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  8. nipon0007

    nipon0007 New Member

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    Today, It is come back fail!! The voltage is swing output.
     
  9. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

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    Hmm that's pity, but I think check the 300N03S mosfet ic.
    As far as I have measure it, it's the only place were this 3v goes to.
    As far as I measure it it's also related on the other side of this ic to the onboard tuners.
    Disable one of them, or both to see for improvement.
    When disabled both, use a external tuner into the tuner slot for this test.
     
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  10. nipon0007

    nipon0007 New Member

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    the 300N03S is find on a dreambox tunner board? On Tunner DM800hd have?
     
  11. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

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    Yeah the 300n3s is placed on the dm800hd satt tuner parts side pcb number T500 close to the lnbp21pd chip.
     
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  12. nipon0007

    nipon0007 New Member

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    If the output 12V is swing What is to Bad?.
     
  13. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

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    Normally I would first try it with another power supply.
    But to give some ideas....

    1. The power supply unit, amps issue.
    2. If you use a 3,5 inch hdd, mainly older types it could be due the amps consumption, better to use a 2,5 inch hdd which only use the 5v to operate.
    3. The tuners are also use the 12v, as you can see on this drawing, maybe there is something wrong with it or the other parts connected on this circuit.
     
  14. nipon0007

    nipon0007 New Member

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    The solution, I do have 3.3 v new board.

    6880.jpg
     
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  15. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

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    Yes that is also a solution, cleverly/well done. :cool:
     
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