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Switching power supply repair

Discussion in 'General Electronics Chat' started by lynx, Apr 10, 2014.

  1. tvtech

    tvtech Well-Known Member Most Helpful Member

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    You are loosing me now. Something very basic is still wrong..

    Does this unit belong to a Customer or is it yours...I specifically ask this because you are spending way too much time on this in order to make any money if it belongs to a Customer. Unless of course it was kind of working from the Customer and then all went for a pile of poo in your hands...

    Tell me please :nailbiting:

    Regards,
    tvtech
     
  2. lynx

    lynx Member

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    hahah... it's mine!! :D and i will be very glad if i can fix it... :) i don't know what i did wrong in the first place but after i revived it...i had that issue with the hot lm317t and then i've opened this thread here.
     
  3. alec_t

    alec_t Well-Known Member Most Helpful Member

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    If plugging the connector in increases the LM317 input voltage perhaps a short in the connector or its wiring is causing a higher voltage to over-drive the LM317?
     
  4. dave

    Dave New Member

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  5. lynx

    lynx Member

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    a capacitor short on the processing board maybe? tried to check for shorts between the processing board pins..but i couldn't understand
    if something was wrong...some voltage pins had high resistance relative to GND some other had low resistance.
     
  6. tvtech

    tvtech Well-Known Member Most Helpful Member

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    Ahhh. That explains all.

    Lucky you :). I had this image in my head that you were in crap because a Customer wants his/her player...and you cannot give it back because it is worse off than when they brought it in :arghh:

    At this stage then lynx, you have the time to check all that has been posted here thoroughly.

    All the guys here who have contributed will keep scratching their heads and thinking...it's something basic we have missed.

    All the best,
    tvtech
     
  7. lynx

    lynx Member

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    haha...

    no matter how much i think of it..i can't resolve that issue...because i understand nothing!
    i can't explain how the input voltage of the regulator can raise just because of the connector.

    i don't see how these two can be relative... only thing i can think is if there is a short
    on the processing board so the PSU raises the voltage to compensate...but the rest of
    the voltages seems normal, so it can't be that.
     
  8. tvtech

    tvtech Well-Known Member Most Helpful Member

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    Wrong. You are another Fez in the making. You are intelligent, you listen and you try and learn. You are the kind of person I have unlimited time for.
    No smartness or arguing or stupid questions..huge time for Folks like you.

    We may not ultimately solve your issue with the player....gonna keep trying though.

    Check out Fez here:http://www.electro-tech-online.com/blog-entries/teardown-3-1-5kw-motor-speed-controller.742/

    What a nice person he is :)

    Stay well, stay strong...and let ETO guide you along that crazy path that leads to Technical knowledge without all the unnecessary complications along the way.

    Regards,
    tvtech
     
    • Thanks Thanks x 1
  9. lynx

    lynx Member

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    thank you so much for your good words... :joyful: i value the help you guys offer
    me on this thread because i really really want to fix this player and not dump it...

    also if any other member has a word to say about the issue with the regulator it's fine!
     
  10. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    If any supply is loaded past what it's specs are, then then the unregulated voltages would rise. Most switching power supplies are tested with "minimum loads" on each output.
     
  11. alec_t

    alec_t Well-Known Member Most Helpful Member

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    Try replacing D108 and C107.
     
  12. ronv

    ronv Well-Known Member Most Helpful Member

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    12vl and 32v are nest to each other in the connector. Could a pin be bent shorting them together. Measure the output of the 12 volt regulator. It should still be 12 volts.
     
    • Thanks Thanks x 1
  13. lynx

    lynx Member

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    they look ok, also all the capacitors have been changed with better quality other than C129 which is behind
    the heatsink of the lm317.

    it's always around 12v (11.45v) no matter if there's a load or not
     
  14. MrAl

    MrAl Well-Known Member Most Helpful Member

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    Hi,

    If the voltage is too high then that means something in the feedback circuit probably isnt working right.

    Since they use an opto coupler for feedback, it could be that the gain has changed too much. Then again it could be anything else in the feedback circuit too.

    Alternately, the load on the +15v section or the +12v section isnt what it should be. If it is too low it may not load the transformer enough.
     
  15. alec_t

    alec_t Well-Known Member Most Helpful Member

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    Even if D108 "looks ok" it may be failing under load. I'd still try replacing it.
    Did you check for a bent pin as Ronv suggested?
     
  16. lynx

    lynx Member

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    1. The D108 must be "UPM F540" i dont know what diode that is..is it fast? also there are no bended pins anywhere..do you suggest i also change optocoupler?
    is it possible to be a grounding problem? i was checking the PSU outside the dvd-r unit
    so it's not grounded anywhere.
     
    Last edited: Apr 22, 2014
  17. lynx

    lynx Member

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    OH MY GOD... it started!! while i wrote if it could possibly be a grounding issue... i thought to myself why i ask and i don't try and see
    and it worked!!! but was the problem really that?....
     
  18. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    I as thinking that although a bit late. I did notice that the grounds were isolated as they should be and connected at the load.
     
  19. lynx

    lynx Member

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    meaning i can disconnect the board so i can fix a joint underneath...or is it going to stop working again?
     
  20. tvtech

    tvtech Well-Known Member Most Helpful Member

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    OK. Now you have to make sure it was.

    Connect everything up as if it is in the "box" ALL the various wires and plugs. But the PSU must be outside.
    Try and monitor the Chopper IC and the 12V rail to make sure they are not hot or unhappy.

    You do not need to do this for long....just make sure all is working. Carefully now.
     
  21. lynx

    lynx Member

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    what if it stops working and we return to the previous state? can we find a way to revive it again?
     

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