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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    Hmm are you sure that the 0 ohm resistor R238 under the cpu is passing true, see drawing diisplay-connector-info.
    Are you sure that your front display is working.
    Are you sure that your simcard is good, and so does not have a internal short.
    And, be sure that the famous Q8 circuit is fine.
    More about this, see the sim-card-issues topic

    But also, did you have checked the serial port if it gives some information with a 0 modem serial db9 cable.
    Tested without and with a simcard/front panel.
     
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  2. Miguel Angel

    Miguel Angel New Member

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    sim card socket tension no sim card
    pin 1->0vcc
    pin2->0vcc
    pin3->0vcc
    pin4->0vcc
    sim card socket tension with sim card
    pin1->1.53v
    pin2->0v
    pin3->0.26v
    pin4->0v

    Q8
    pin D 1.53
    pin G 4.98
    pin S 5.00

    Q9
    pin C 4.99
    pin B 0.0
    pin E 0.0
     
    Last edited: Oct 26, 2016
  3. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

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    sim card socket tension with sim card
    pin1->1.53v

    Could mean that the simcard has some issues so that it lowers the pin 1 voltages.
    Be sure that your simcard is good, and check the pin 1 or q8 center pin on the behavior, normally it should give 5v, then low without simcard while you turn on the motherboard.
     
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  4. Miguel Angel

    Miguel Angel New Member

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    Q8 changed original, but there are still 1.54vcc in pin D
     
  5. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

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    I assume that you mean...
    Still 1.54 vdc if you have the simcard in it, and not.
    Or, without sim, 5v, then drops to 1.54 vdc.
    With sim, same behavior.

    This happens as well with the q8 center pin and the simcard holder pin 1.
    If so, check the voltage both sides from the Fuse F2, see if it's drops on one side.
    But it can also be caused due a defective sim.
     
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  6. Miguel Angel

    Miguel Angel New Member

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    fuse f2 is 5.01v, the 1.54v simcard in it. without sim front red led flash, without sim card Q8 center pin is 0 vcc. U16 fault?
     
  7. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

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    Could be, but in all my xxx repair cases I had twice that it was due the U16, so it's rare.
    Normally I would think of a defective sim card, but I assume you already have tried it with another sim.

    In any case, you should receive a terminal output when the sim has been removed.
    So my advice is to connect the motherboard to a computer with the serial cable and see with hyperterminal or putty if you receive the boot data from the motherboard, so also if it's healthy.
    Bps setting is normally 115200 and in some rare cases 57600 bps.
     
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  8. raza05

    raza05 Active Member

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    Hi Johnny
    Hope you are fine
    I have same problem with DM 800 it's sunray 2.01 here are the voltage details
    on P5
    1 1.21
    2 2.57
    3 3.26
    4 3.23
    5 5.0
    6 11.9
    7 gnd
    8 gnd

    pin1 L13 1.21
    pin2 L13->1.18

    pin1 L14 ->2.57
    pin2 L14->2.54

    pin1 L7->2.56
    pin2 L7->2.56

    pin1 L20->2.56
    pin2 L20->2.56

    pin1 L10->2.56
    pin2 L10->2.56

    pin1 L6->1.20
    pin2 L6->1.19

    pin1 L21->1.21
    pin2 L21->1.21

    pin1 L11->1.21
    pin2 L11->1.21

    pin1 L12->1.21
    pin2 L12->1.18

    On R 238 3.24

    U25

    Pin 1. 0
    pin 2 . 0
    pin 3. 0
    pin 4. 4.89
    pin 5,6,7,8 . 1.18

    u23

    pin 1,2,3, . 1.18 v
    pin 4 .1.63
    pin 5,6,7,8 . 12 v

    Front panel voltage (with sim & FP Installed )

    top

    2.5 0 0 0 0 0 0 0 0 0 3.4

    Bottom

    3.24 5 3.3 3.3 2.24 --0.21 0 0 0 0 0

    it's strange on pin 5 the voltage fluctuate & drop to 0.21 from 2.24

    any suggestions ?
     
  9. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

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    Connect/see if the serial rsdb9 service port still gives some data output into a terminal screen from putty/serial mode.
    Check the board without connected a front panel and tuner, see if it than comes to life.
     
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  10. raza05

    raza05 Active Member

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    Thanks for the quick reply ...just checked the db 9 port with sunray flash up ..no response ..& also checked without tuner + FP ..no response just lan leds are working
     
  11. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

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    Than it could be a related to the cpu, maybe the Y1 crystal because if that not works, than the box is also death, while all voltage are fine.
     
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  12. raza05

    raza05 Active Member

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    there are no voltages on crystal Y3 should i change change all these three ?
     
  13. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

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    No voltage on the crystals could mean that the cpu is no longer active, check all conductors to it if one of them is interrupted.
    When one crystal has no voltage, than it could be caused due a shorten part on the circuit, but again, these crystals are mainly connected to the cpu, i do somewhere a picture posted how these are connected to the cpu, but right now I couldn't find it, thus by doubts if it could be a crystal, then I think best is to replace it.

    Be aware that it may also be caused due a cap, ceramic or normal caps.
    I often replace the four big caps before going further with the repair because at least 3 of them are for the cpu 1.3v.
     
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  14. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

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    This may also help you with it.
    Especially the part about... Or, if you have,...
     
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  15. raza05

    raza05 Active Member

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    Thanks Johnny ... You are great & really a savior ... I replaced the caps one by one but no luck ..any ways I 'll check & post further updates on this
    Thanks again

    Ok so far I have checked all the voltage under , check all conductors
    all voltage are good one thing I observed & checked again & again that without Sim the volts on crystal Y3 are from 0.5 to 1.0 ( varies irregularly ) I think it's the processor trying to read/work
    I missed one thing which is my mistake that under the dc main volt input Pin main board is little busted /Damaged definitely because of power surge I am uploading the Picture here but the voltages are fine around these C286 & I also checked the voltage on L5 & C 123 & 124 they are 2.5 v
    that's the update so far One more thing the 4700 uf caps are bigger in size ( smalls are not available in Market ) so I have to soldered them with wire to check Can I install 3300 uf they are available in small size
     

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    Last edited: Mar 9, 2021
  16. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

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    Since I've never changed the 4700 uf to a lower uf value, I can't give you a confirmation of it but it may be possible that the board should work with the 3300 uf.
    It may also work with one 4700uf cap instead of the three.

    As for the ground damage, this seems to be good enough repaired.
     
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  17. raza05

    raza05 Active Member

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    So there is No need for L37 ...Thanks Again for a valuable reply ...great man great job
     
    Last edited: Mar 10, 2021
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