DM8000 PSU not working

Discussion in 'Hardware troubles and Repair support.' started by Greystoke, Apr 3, 2017.

  1. Greystoke

    Greystoke New Member

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    Hi,

    I am only getting voltages on the 2 pins in RED in this image.
    All other pins are measuring 0 volts.

    Can anyone help with this please.
    [​IMG][/IMG] [​IMG]
     
  2. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

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    Psu 25x10
    14v issues are mostly related due the IC101 hot zone.
    Also, the lower 2.2v could be due the defective IC101.

    Psu 5L0565
    14v issues are mostly related due the Q3 hot zone.
    Also, the lower 2.2v could be due the defective Q3.
    But in some cases due a defective ICI
     
  3. Greystoke

    Greystoke New Member

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    I replaced caps to day on the PSU as some were expanding.
    The ones in red were changed.
    Could these cause the voltage issue if one was bad.

    Is this PSU the 25x10.

    [​IMG]
     
  4. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

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    Yeah could be damaged due a defective cap thinking of heavy load to the 14v circuit or it's just a defective cap that cause the 14v drop.
    However, best is also to use the same value caps, and not to high load voltages.
    For example a 100uF/16v cap replacement to 100uF/60v may give issues due the longer load.
     
  5. Greystoke

    Greystoke New Member

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    I replaced them with identical value and load voltage as on the original ones.
     
  6. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

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    Ah, okay in that case you need to examine the IC101 from the hot zone.
    More about this, see this topic.
     
  7. Greystoke

    Greystoke New Member

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    I just removed IC101 and measured it.

    [​IMG]
     
  8. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

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    Seems to me good, and I assume that the other way measurements are also in the range.
    I think than, check the diode D200, it's on the cold zone and close to the big transformer T100.

    But I do not know how you test the psu, but if it's connected to the main board than it could be due a issue from the main board itself.
    Best is to test the psu when it's disconnected from the main board.
    More about this, see this topic.
    In any case, you must have the 14v even when it's disconnected from the motherboard.
     
  9. Greystoke

    Greystoke New Member

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    [​IMG]

    The Diode D200 measured:
    0.496
    reversed probes
    0

    I have the PSU removed from the mainboard.
    14v is the problem.
     
  10. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

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    Okay, so that is also not the issue.. Hmm than it become tricky to find the reason why it collapse.
    Maybe it helps you if you take a look on this schematic, it's not the same, but some basics related to the 14v are.
    Another thing I think of is the IC200 or a issue with the PC100/PC200 but that is rare.
     
  11. Greystoke

    Greystoke New Member

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    Is there any way to test IC200/PC100/PC200.

    Do you think there is any point putting back in the original Caps
     
  12. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

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    If it has arises after the cap replacement than it could be that you have used a bad cap or damaged a print track.
    In that case it's wise to examine the replaced caps.

    And yes there are ways to test optocoupler, search with google to optocoupler test
     
  13. Greystoke

    Greystoke New Member

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    All original caps are now back in.

    Still not getting the 14v
     
  14. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

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    I think take a good picture from the pcb cold zone, and see if you find some solder short, or let me see to it.
     
  15. Greystoke

    Greystoke New Member

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    Before I changed the caps the box was having issues.

    Over the last month it was getting harder to power on the box.

    When I would switch it on I would just get a blue light or a flickering blue light.
    After switching it on and off a few times it would eventually power on.
    That was why I replaced the caps.

    The voltage may have been intermittently low on those occasions.

    [​IMG]

    [​IMG]
     
  16. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

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    So in fact you had problems before replacing the cap.
    At least I can not see anything special in your photos, it all seems fine.
    So there must be something defective, and I think an optocoupler, PC200 or PC100.
     
  17. Greystoke

    Greystoke New Member

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    I notice I get about 8v on the connector when not connected to the Mainboard.
    I get 3.25v when connect to mainboard as in the first image.

    I have swapped PC100, PC200 and PC300 with each other and the voltage still stays at 8v on the connector.

    Also with PC100, PC200 and PC300 removed off the PSU still 8v
     
    Last edited: Apr 4, 2017
  18. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

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    Hmm, okay in that case, I'm out of options.
    My best advice is for now to check each component that is connected to the 14V circuit.
    And tomorrow I can do some experiments with this 14v circuit, maybe I'll find something.
     
  19. Greystoke

    Greystoke New Member

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    I think I have checked everything, but still can't find what is causing the voltage drop to 8v.

    Hope you can find what is causing this when you do some tests.
     
  20. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

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    Okay, lets see if you get the correct voltages from the T100 transformer.
    Remove the L200 jumper.
    When removed you should measure 48,7v dc on the L200 T100 side, and on the connector cn300 14v side nothing.
    Measurement, cold side, Ground and the Measurement spot.
    Psu unbalanced, not connected to the motherboard.
    Be careful with measurement, do not create a short between this 48.7v and the ground and unload the caps before you work on the psu.