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dvd player repair

Discussion in 'Troubleshooting and Repair' started by jeff2005, May 13, 2010.

  1. jeff2005

    jeff2005

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    May 13, 2010
    i have a portable dvd player im trying to troubleshoot. I found that a fuse was blown and replaced it but everytime i plug it up the fuse blows again. what should i troubleshoot first i thought it might be a transistor there two right next to each other?
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,171
    2,687
    Jan 21, 2010
    It could be a transistor, or it could be almost anything else.

    You need to have some rational method of figuring out likely suspects.

    Start with an examination of the board. Many components will show signs of failure (but beware of components which are just being operated close to their limits and may be scorching the board -- especially true of wirewound resistors).

    If there are no visible signs, there may still be the smell of the magic smoke that was released -- there may also be marks on the case where the smoke went. This may lead you to a particular area.

    If a fuse blows, then the fault is obviously one that causes high current to flow, so start checking components that are capable (if shorted) of causing large currents (e.g. output stage, filter capacitors, some diodes).

    Next step is to disconnect the load from the PSU (careful of this as the PSU may require a minimum load) and check if the fault is in the PSU.

    Then there's lots more you can do before you start replacing (or suspecting) components at random.

    So the first question therefore is, *why* do you think it's this transistor?
     
  3. jeff2005

    jeff2005

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    May 13, 2010
    i dont think its the PSU if i plug up just the psu then the fuse dont blow, but if i plug the psu into the circuit then it blows. so it shouldnt be the psu should it?
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    External power supply? That should ease any suspicion on it for the moment.

    How about all the other things I mentioned?
     
  5. jeff2005

    jeff2005

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    May 13, 2010
    no its not external ps but the ps circuit on has the switch and a diode then the fuse, after the fuse it has 5 wires that plug into the circuit of the dvd player.

    I dint see anything burnt of smells like it was burnt. still working on testing anything that might cause high current.
     
  6. jeff2005

    jeff2005

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    May 13, 2010
  7. Resqueline

    Resqueline

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    Jul 31, 2009
    That's a coil, or an inductor if you will, lying on its side. The silkscreen print should say L-something. It doesn't look burnt but there's some kind of deposit around it.
    Is the any smell of the deposit? Does it clean easily? Has C614 ever been there btw.?
    Apart from that I can't contribute with anything more than steve's already done. You mention fuses & transistors but we can't see them from here, so...
     
  8. jeff2005

    jeff2005

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    May 13, 2010
    i dint know what the yellow stuff was on that part it goes all the way over to the capacitor, i was think it was not supose to be there. is the capacitor was leaking would it be a yellow color?
     
  9. Tesla

    Tesla

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    May 10, 2010
    How did it become not working? Knowing this might help in trouble-shooting it.

    For instance, portable devices often end up being used in places they probably shouldn't be (like around food and drink). Did something get spilled in it?

    Also, portable devices get moved around and sometimes dropped. In this case you would be looking for a hair-line crack on the board.

    You said the power-supply is internal, but since these devices often get separated from it's AC adapter, I often see them getting blown up by people using the wrong AC adapter on them (just because the plug fits) :eek:

    As far as the power supply goes ... how much voltage is it putting out?

    You might try disconnecting the optical drive and see if the PS will power the main board without blowing the fuse.
     
  10. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,171
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    Jan 21, 2010
    The yellow stuff looks like glue to me (perhaps to damp the inductor from vibrating). I can't see leakage from anything flowing that way. If it seems like glue and you can't clean it off the side of the capacitor, then it probably is.

    I would suspect that you have removed C614, but if not, it looks like it was once there. I compared it with another set of "unused" holes and they looked very different.

    Leakage from capacitors generally exhibits one of three forms:

    1) explosive -- it gets splattered everywhere. You're not left wondering.

    2) swelling with or without small amounts of localised leakage (day a spot of brown on the top or bottom of the capacitor.

    3) leakage. In this case it goes where gravity takes it. I've seen brown streaks running from a capacitor right down a board (that was mounted vertically) and off the edge, and others only a couple of mm long.

    Where a board is horizontal (and not upside-down) you will expect leakage to form a pool around or on one side of a capacitor. In this case it is conceivable that it could have gone up the side of the capacitor a little, but not up and over the inductor without spreading more widely over the board.

    The colour is generally darker than that too.

    Tesla's question regarding the history of the device and the fault is important (and I thought I'd asked, but it may have been in another thread about something else)
     
  11. jeff2005

    jeff2005

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    May 13, 2010
    no this device was only mounted to the back of a cars headrest, we had it for about a year and a half then one day we tryed pluging it up but it wouldnt do anything. thats when i desided to take it apart to see what i could do sence this is what im going to school for. if someone did plug the wrong adapter into the dvd player what does it hurt i dont think anyone ever did?

    the power supply has 120v going to the main board, I'll try your idea tomorrow about seeing if the ps will power just the main board without blowing the fuse.
     
    Last edited: May 17, 2010
  12. Tesla

    Tesla

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    May 10, 2010
    A different adapter could be a different voltage or polarity.

    EDIT: It has 120v but you use it in the car?
     
    Last edited: May 17, 2010
  13. jeff2005

    jeff2005

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    May 13, 2010
    i think if it was a wrong adapter it would have been the same volts because its coming out of a 12v power source, but dont know about the polaritys. so if the polaritys was wrong what would it mess up inside the device?


    C614 was never anything there
     
  14. jeff2005

    jeff2005

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    May 13, 2010
    no its got a 12v power source from the car then it plug into the ps in the dvd player which has a on off switch then a diode and a fuse which then goes to 5 wires that plug into the main board but on the ps it says that it has 120v at the wires going into the main board.
     
  15. Tesla

    Tesla

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    May 10, 2010
    Connector voltage polarity ... as in the positive and negative are reversed ... yes, that would be bad. Luckily, (if it's a common round plug) the outside is usually negative and the inside is positive.

    No, I'm pretty sure a power adapter (even car ones) can be made to output different voltages. It depends on the circuitry inside the adapter. Often, the adapter's output voltage is written on it ... or where it plugs into the DVD player case.
     
  16. Tesla

    Tesla

    165
    2
    May 10, 2010
    If you really want to fix this device ... the make/model and some better pictures would go a long way.

    From your written description so far ... I find it unlikely that 120 volts are involved. Do you think maybe the 120v is describing the rating on the fuse?

    Speaking of the fuse ... are you sure you are replacing it with a fuse of the exact same rating (amps/voltage/Fast-Slow) as the one you originally pulled out?
     
  17. Tesla

    Tesla

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    May 10, 2010
    I see where it says 125v ... yes, that appears to be part of the fuse rating ... 3A @ 125v ... never install anything bigger. What kind of fuses have you been using as replacements?

    On the original power adapter that plugs into the car ... what does the label say on it about the output voltage? When you double check it with a meter, what do you get?
     
  18. jeff2005

    jeff2005

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    0
    May 13, 2010
    i had to use a different kind of fuse because the original fuse looked like a resistor and couldnt find one to replace it with so now im using a circle fuse at [email protected] the original adapter doesnt have a anything on it but i know it came with the dvd player. on the side of the dvd players case it says car plug 12V, DC in 9V.
    can u test a diode in the circuit?
    when i tested the adapter i got 12.32V DC
     
    Last edited: May 18, 2010
  19. Tesla

    Tesla

    165
    2
    May 10, 2010
    To get an accurate check on a diode, you usually have to unsolder at least one leg (so you aren't reading other parts of the circuit).

    That's what I thought ... the player runs on 9v DC (not 12v DC). It sounds like the adapter might not be stepping down the voltage properly. See what the cig-lighter socket voltage is. On my Honda, it's 11.8v . Compare the adapter's input voltage to the output voltage. I would think there should be a 25% decrease (if the adapter is working properly).
     
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