DM500HD Nothing works U1102 (4128) is heating

Discussion in 'Hardware troubles and Repair support.' started by mukix, Nov 18, 2016.

  1. mukix

    mukix New Member

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    Hello
    over the night the dm is going down. nothing works just hear a small zzzz ton.
    Voltage on P1100 :
    1: 0,12V
    2: nothing
    3: 0,6
    4: 0,33
    5: nothing

    the U1102 (4128) is heating after 10 sec when on.
    and from the 2742 , i think its comming from him, hear a small zzzz
    USB,front is unpluged
    what can be the problem? Sorry for my bad english!
    Thanks in advance
     
  2. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

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    Hmm, it seems to me a issue with the 5v delivery.
    The U1102 may heat up due the lost of the 5v to the U1101 Vcc pin, but it is still feed with the 12v U1100.

    I think, because you have nothing at pin 2 (1.8v) which goes to the LT1580 and the 5v goes to the VControl and missing the pin 5 (5v), so it will not be working.
    Other sources are still whiling to give some voltages, so you may assume that they are fine.
    Therefore it seems to me a issue with the 5v delivery.
    See the P1100 pin 5 information drawing and check the 5v circuit.
    Maybe the U1104 itself is become defective, or a 0 ohm resistor as the R1125 may be interrupted.
    Also it could be a interruption with the L1106.
    In any case, check the 5v source and circuit, best is to do it with ohm measurements.
     
  3. mukix

    mukix New Member

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    Thank you very much for your quick answer.
    I will do it now
     
  4. mukix

    mukix New Member

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    Before 2 hours ago i have look the 3 pin sircuit and interrupt the L1100 (1R5) than the zzz was gone and i have the 12v back on U1100 input (before it was just5V). Than i interrupt the R1125/ R1104-R1101/ R1119-R1112/ R1132-R1130 and Vpower from LT1580 ALL with no results. I remove all capacitors c1107...c1109,40,41,33 and now i have:
    1: 1V
    2: 1
    3: 2,4
    4: 3,25
    5: 2,3
    and the zzz ton is going to slow tak tak
     
  5. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

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    1: 1V
    If you have removed the zero ohm resistors R1132/R1130 then this 1.3v circuit cant work.
    It needs the 2.6v delivery.
    But also the 5v to the LM, otherwise it won't work.

    2: 1
    This one needs two voltage to operate, 5v and 2.6v
    So, because you missing some voltage it won't work.

    3: 2,4
    You get probably this voltage due the 12v delivery to the U1100, but to low due the missing 5v to the LM

    4: 3,25
    This one is okay because it needed only the 12v to operate.

    5: 2,3 (U1108)
    After the removal of the R1125 you should have the 5v, if the 5v Dc to Dc circuit works.
    Maybe a diode issue, Check the diode and zener diode D1108 or else it coul be a defective LT1940
    Note that on the drawing there is a wrong number, U1104 should be U1108
     
  6. mukix

    mukix New Member

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    Hi Johnny,
    i cant find it.
    when i interrupt R1125 i have 4,8V on SW1 and the 5leds are blinking.
    i was checking the 5pin and when i interrupt the LM1580 line i have 4,5 V.
    And the capacitors i have change on PG1 than i have the all 5 V on SW1 but now anything is happen and all is the same as at the begining
     
  7. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

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    Yeah 4.5v seems to me a bit to low.
    Normally, when the R1125 has been removed you should measure the 5v on the coil L1118 both sides.
    And in my case (original board just tested) the mobo leds are normal, four on, center led off.
    Tested without the sim card.

    But okay, as you say, you now have the 5v.
    That is, assuming you have all the bridges as the zero ohm resistors and L inductors replaced.
    And assuming that they all are good placed.

    So, now remains the question,
    You have all the voltages as the same before, or are there some differences.
     
  8. mukix

    mukix New Member

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    its the same before.
     
  9. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

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    Hmm okay, then I think of a cpu issue which involves most of the voltages.
     
  10. mukix

    mukix New Member

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    Hi Johnny,
    I have it. It was the adapter. 3 times i measure the 230ac to 12dc Adapter and it shows me 12,1- 12,3. I dont know whats the problem on first time with heating U1102. I have just change any capacitors. Maybe nothing was defectly and it was the result when the adapter losing power.
    The 25v 1000uF was "explode" in the adapter and he gives 12,1V but no power.
    best regards
    muki
     
  11. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

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    Ah, the famous psu issues...
    Strange symptoms due only a faulty psu, but it happens more often that it could be a psu issue.
    Mainly due a amps delivery which may become bad at age.
    Normally it is the first thing that needs to be done with box issues, testing it on another psu and I thought you already had tried that.
    But okay, glad/lucky you have tried it with another psu to discover that it solved the problem.

    Thanks for your given solution which is a lesson for others,
    Always test the box with another psu before thinking of a hardware fault with the motherboard. ;)