Dm800hd death, no oled display, only two lan leds on.

Discussion in 'DM800HD Hardware troubles and Repair support.' started by Johnny B., Nov 2, 2015.

  1. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

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    Dm800hd death, no oled display, only two lan leds on.
    Further no terminal output from the comport and all voltages from the P5 (fault finder) pins are fine.
    Sim card pin 1 voltages stays on 5v.

    With this case it was the crystal JWT54.000 pcb number Y1.
     
  2. arcadeswede

    arcadeswede New Member

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    I'm having this exact problem.
    All the voltages on P5 (fault finder) are OK. Voltage on pin 1 on SIM-card is 5V.

    Could this be the crystal Y1 as well for me or is there a schematic for troubleshooting this particular problem to figure out which component is bad?

    Thanks!
     
  3. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

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    Yes it is possible, and it happens more often that it is a problem with a crystal.
    But of course, it is not always the case, it may also be a cpu problem.

    Further measurement procedures are of course possible, such as the measurement of the crystal.
    Usually this is done in frequency with a scope, with a multi-meter you will see the dc voltages, with good connection to the cpu will give the two crystal pin a similar value.
    By different value between the two, it may be a CPU problem.
     
  4. arcadeswede

    arcadeswede New Member

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    I measured the crystal Y1 over the two pins and got 1.6V on both of the pins. So does this means the CPU is ok?
    How about the crystal? Can I measure it with a multimeter that has Hz-function to see what Hz it provides and determine if the crystal really is the problem or have I just confirmed that?
     
  5. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

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    Both voltage are fine, and this mean that there is on both pins a connection to the cpu.
    It is also better to measure the other crystals on the same way to see if they also are good connected to the cpu.
    The voltage of the others are ofcourse not the same as the Y1.

    Measuring 54.000 Hz with a multimeter, maybe.. but it depends if the device can measure this frequency.
     
  6. arcadeswede

    arcadeswede New Member

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  7. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

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    A bit doubtful due older type/model but it may work.
    However I would buy the same model/type.

    This you can find here on Ebay.com
     
  8. Miguel Angel

    Miguel Angel New Member

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    I have the same problem, I changed Y1, but still the same.
     
  9. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

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    Yeah sometimes it is due the crystal, but not always.
    But be sure that you have the 2.6 voltage, lower as 2.3v could mean a defect with the U7.
    The cpu itself give a feedback of 2.3v, the U7 puls it up to 2.6v.

    Also the caps C112/113/114 or even the C115 could also cause this.
    They may look good, but may have issues with loading.
    And offcourse the cpu itself may also the cause, but mostly you see than also a issue with the 2.6v voltage.
     
  10. Miguel Angel

    Miguel Angel New Member

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    the caps C112/113/114 changed to 4700uf 16V chinicon,or even the C115, and U11 AP2146 and U18 7702 changed and crystal 54mhz changed.
    result: red led on in display and two lan leds on, but the fan is off, previously only leds on lan only, the main board is DM800 REV:L / 94V-0 20110318.

    Volt with SIM card +5.0V

    Volt U27
    PIN1->11.97v
    PIN2->0v
    PIN3->0v
    PIN4->0v
    PIN5->5.0v

    R299->2.62v
    R300->1.29v
    R297->1.29V

    Volt U20
    OUT->3.31V
    IN->5.0V

    Volt C112
    -->GND
    pin+->1.29v

    Volt C113
    gnd-
    pin+0V

    Volt C114
    gnd-
    pin+0V

    Volt C115
    gnd
    Pin+->3.31V

    Volt Q10 MMBT3904(1AM)
    pin 3 colector ->5.0V
    pin 2 emiter -> 0V
    pin 1 base -> 0V
     

    Attached Files:

    Last edited: Oct 21, 2016
  11. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

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    As far a I see it you have some issues with the 12v feed to some dc to dc ic's.
    You can use this drawing as a references, it's basically the same build.
    dm800hd-rev-m-g-mainvoltagemeasurements
     
  12. Miguel Angel

    Miguel Angel New Member

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    new problem found, the power connector on the hard drive has no power or + 12VDC or + 5VDC, all tensions in U20, U26, U27, U28, U29 are corect according to the plane dm800hd-rev-m-g-mainvoltagemeasurements,
    power adapter tension +12.05 vcc.
    from where the voltage of +12 VDC for the hard drive and fan?
    from where the voltage of +5 Vdc for the hard disk?
    the main board is DM800 REV:L / 94V-0 20110318.
    can not I find the circuit VCC +12.
     
  13. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

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    There is as far as I know no 12v for an hdd with the dm800hd, only 5v for a notebook hdd.
    And, this 5v is not directly present, it's feed when the box is booting.

    Also, since you have all the voltages from the dc to dc ic's, then there is no doubt that the 12v circuit is fine.

    So, because you have all the voltages, and the box gives only two lan leds, and the red led on the front.
    Then I'm starting to think of a cpu issue, or a issue with the U18 which also may cause this symptoms.
    Theoretically, the box could work without the U18, at least with the older type motherboards.
    It's basically used for the network poe option.

    But I assume that you test the box without the tuner, otherwise could this also be the case.
     
  14. Miguel Angel

    Miguel Angel New Member

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    U18 7702 changed.
    but pins P5
    pin1-> 1.23v
    pin2->2.62v
    pin3->3.31v
    pin4->3.3v
    pin5->5.03v
    pin6->11.90v
    pin7->gnd
    pin8->gnd
    but diode D16 and D21 is 1.31v, pin1 voltage is not correct 1.23v U26 fault?
     
    Last edited: Oct 24, 2016
  15. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

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    Strange values, especially the 11.90v and 5v which I never had seen.
    It should be something as this,

    dm800hd-U18-Snap.jpg

    Ah, I thought it were the U18 measurements, but they are the P5
    In that case they are fine.

    D16 and D21, they are both connected to the U26 pin 5/6 output which must be around the 1.3v.
    So to me it seems also fine.
    As for the pin 1 feedback pin, this is around the 1v (0.8v) which is normally lower than 1v, but a bit higher may also.
     
  16. Miguel Angel

    Miguel Angel New Member

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    change the power adapter 11.97vcc

    U18 voltages
    pin1-> 2.51
    pin2->3.31
    pin3->3.11
    pin4->gnd
    pin5->3.31
    pin6->0
    pin7->2.74
    pin8->3.31
    R137 p1-> 3.31 p2->2.09
    R138 p1-> 3.31 p2-> 2.12

    U26 voltages
    pin1->0.8
    pin2->5.02
    pin3->11.57
    pin4->11.96
    pin5->1.31
    pin6->1.31
    pin7->0
    pin8->0

    U27 voltages
    pin1->0.80
    pin2->10.40
    pin3->11.56
    pin4->11.96
    pin5->5.03
    pin6->5.03
    pin7->0
    pin8->0

    U28 voltages
    pin1->0.79
    pin2->11.17
    pin3->11.57
    pin4->11.97
    pin5->5.03
    pin6->5.03
    pin7->0
    pin8->0

    U29 voltages
    pin1->0.79
    pin2->3.0
    pin3->11.56
    pin4->11.97
    pin5->2.64
    pin6->2.64
    pin7->0
    pin8->0


    tips tester measured in the hole gnd
     
  17. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

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    U26 1.3v voltages
    Input pin3/4->11.57
    Output pin5/6->1.31

    U27 5v voltages
    Input pin3/4->11.56
    Output pin5/6->5.03

    U28 5v voltages
    Input pin3/4->11.57
    Output pin5/6->5.03

    U29 2.6v voltages
    Input pin3/4->11.56
    Output pin5/6->2.64

    All are fine, only I missing the 3.3v Dc to Dc measurements but since you already have told that you have twice 3.3v is this also present.

    Based on the measurements, and the fact that the U18 also is fine then I'm afraid that this issue is a cpu or memory problem.
    Or the cpu or memory block itself, or some interrupted print track or missing voltages.

    As for the cpu voltages...
    See this picture, and check the inductors (L parts) on both side.
    Both sides must have the same voltages.
    Do the same with the 0 ohm resistors, these are resistors with one or more zero on it.

    DM800HD-cpu-1-3-2-6-vdcspots.jpg

    Good luck.
     
  18. Miguel Angel

    Miguel Angel New Member

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    pin1 L13->1.23v
    pin2 L13->1.19v

    pin1 L14 ->2.62v
    pin2 L14->2.62

    pin1 L7->2.62v
    pin2 L7->2.62v

    pin1 L20->2.62v
    pin2 L20->2.62v

    pin1 L10->2.62v
    pin2 L10->2.62v

    pin1 L6->1.23v
    pin2 L6->1.21v

    pin1 L21->1.23v
    pin2 L20->1.23v

    pin1 L11->1.23v
    pin2 L11->1.22v

    pin1 L12->1.23v
    pin2 L12->1.19v

    tips tester measured in the hole gnd

    resistors no zero ohms ,the image
    The CPU is a little hot even off, 43 CÂș.
     
    Last edited: Oct 25, 2016
  19. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

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    Okay so there is no measurable reason why the motherboard fails.
    However there is a place that always gives a differences when there is something wrong with the motherboard.
    And that is the P2 display connector.

    Healthy is, (note: top row voltage 8.9 may be higher till 12v dc)
    top row,
    2.9 - x.x - x.x - x.x - x.x - x.x - 3.3 - x.x - 8.9 - x.x
    Bottom row,
    3.3 - 5.0 - 3.3 - 3.3 - 3.3 - 3.3 - x.x - 6.9 - x.x - x.x

    More about it, see this images.
    But be careful with the measurements here, do not make any connection between two pins while measuring.

    dm800hd-front-display-information
    Or this one,
    dm800-display-measurements
     
  20. Miguel Angel

    Miguel Angel New Member

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    with sim card
    top row
    square pin 2.65 - 3.22 - 0.0 - 0.0 - 0.0 - 0.0 - 3.31 - 0.0 - 10.52 - 0.0
    Bottom row
    3.31 - 5.02 - 3.31 - 3.31 - 3.31 - 3.31 - 0.0 - 0.0 - 0.0 - 0.56

    It has removed the sim, LED flashing red, but the front is off oled.
     
    Last edited: Oct 26, 2016