Dm800 SE Clone 3.3V Issue

Discussion in 'Hardware troubles and Repair support.' started by gyozo75, Jun 30, 2016.

  1. gyozo75

    gyozo75 New Member

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    Hello.
    I have a clone 800SE,i have issue with the 3.3V on board supply is too high measuring 4.9V on the P1100 pin4,the resistance measured 990 ohm,after removed R1136 i have 3.4 and 4.95 on removed resistor pins.The pcb use regulators LT3830.
    Why i have 4.9V on 3.3V supply line?
    L.E:When i removed the R1136 the receiver booted,on the OLED display i have the message"Dreambox 2nd failed!"
    Help please.
    Thank you.
     
    Last edited: Jun 30, 2016
  2. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

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    When I am at my work location I can give you on this a better answer.
    Because there I have all the notes, which is on Friday night or Saturday.

    But my first thought is faulty Q1105, 5v leak to the source.
    Also, since you're close to the value 914Ohm.
    But still, it could also be caused due another circuit.
     
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  3. gyozo75

    gyozo75 New Member

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    Hello.
    I don't have Q1105,this is another topology...what else i look?
     
  4. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

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    In that case it's better if you give a picture from the type of motherboard you have.
    Or tell me at least which type of motherboard it is, as for example Higo24 RevD6 2011-07-29
    Because there are allot of modifications made while they where in production.
     
  5. gyozo75

    gyozo75 New Member

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  6. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

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    Okay, you have the type motherboard with the 8pins Dc to Dc regulators which you already have mentioned the LTC3830.
    And these regulators are very unstable if the coil has some issues (overheated), or with a overload.
    But also the regulator itself could be the cause, at least assuming that the input is feed with 5v, and adjusted to the output 3.3v.

    Now, maybe it's better to wait till tomorrow so that I could give you some better information about this circuit, because it's now for me hard to tell which ic delivers the 3.3v.
    But if I need to guess, than I think it could be the U7B that delivers the 3.3v.
    And maybe it's some lighting flaws, but if I take a look at you're image, it looks as if some pins has become to hot.
    If this is so, than it's not unlikely that this Ic can't carry the amp consumption, and need to be replaced for a new one.
     
  7. gyozo75

    gyozo75 New Member

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    Yes the U7B is the 3.3v regulator,the input is feed with 12v not 5v.But i think the regulator ok,as i mentioned when i remove the 0-ohm resistor R1136 which is coming from the 3.3v regulator,i measure from the regulator part 3.4v and the other side of the resistor 4.9v and this is the big problem where is coming this 4.9V?
     
  8. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

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    Question, where is coming this 4.9V?

    This I can check tomorrow, that is.. if I have this type motherboard in my workplace.
     
  9. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

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    Did some measurements on the same type motherboard but it's not so easy to say were the voltage come from.
    The removal of the R1136 0 ohm resistor disable the 3.3v to the cpu and other parts.

    Better it to place this resistor back, and remove the L1108 to see if the problem solves.
    If so, then it's probably the L1109 circuit, and this is mainly for the cpu feed.
    If not, then it could be due the parts as the U1108 (ddr regulator), U8, Nand chip, U1204, U700, and some places to the cpu, and also it feeds the tuner 3.3v.
    The only thing I could think of is that the dc to dc regulator has some issues when it's ballast.
    But since you say that you measure nearly 5v on the L1108/L1109 side then it looks as if the Dc regulator is fine.
    Nevertheless, see if you can figure out from which side the voltage comes by the removal of the L inductors.

    Or measure some spots as these, maybe it say's something.
    dm800se-revd13-Snap1.jpg
    The L1109 ?ohm measurement I could not do due a defect of the cpu

    dm800se-revd13-Snap2.jpg
    These are mainly some ohm measurements from the Dc regulator, but I assume that they are fine.