Caravan Battery Charger Resistor.

Discussion in 'General Electronics Chat' started by ss03947, Apr 13, 2014.

  1. ss03947

    Thread Starter New Member

    Apr 13, 2014
    9
    3
    Hi, I'm a complete noob when it comes to electronics, so decided to search the web for an answer, hence my thread on this forum.

    I've recently acquired a caravan which needs a bit work doing to it, & while working on it I've found out that the battery charger doesn't work. A few enquirers advised drilling the pop rivets out of the casing to check the fuse inside, which is OK, but I've noticed a resistor has burnt out. (see photos)

    First photo is of the circuit board itself, second a close up of the resistor.

    The resistor has R17 marked underneath.

    [​IMG]


    [​IMG]


    I feel confident in replacing a resistor, problem is I haven't a clue where to get one the same.

    Could some member advise me/point me in the right direction, or should I just take it to a computer/television shop.?

    Thanks,

    SS.
     
  2. samuel.whiskers

    Member

    Mar 17, 2014
    95
    2
    Replacing it will be easy/cheap.... working out the correct value might be harder....
     
  3. ss03947

    Thread Starter New Member

    Apr 13, 2014
    9
    3
    Exactly, that's the bit I haven't a clue about :D or where to get one :confused:

    SS.
     
  4. samuel.whiskers

    Member

    Mar 17, 2014
    95
    2
    You need a schematic.... where do the traces on the dead resistor go to?
    I'd be concerned a fault elsewhere cooked the resistor??
    A 20yr old charger.... might be time for a new one in any case.... :)
     
  5. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,986
    745
    what is the number of Ic3,it maybe a TL431,also what is the 8pin chip?
     
    Last edited: Apr 13, 2014
  6. BillB3857

    Senior Member

    Feb 28, 2009
    2,400
    348
    Hard to tell from the top picture, but is the large cap opposite the brown and blue wires bulged? If so, it should be replace as well as what ever else is needed to get the unit working.
     
  7. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,548
    2,373
    Seems a bit fancy for a battery charger, by the electronics, at first glance I would have taken it for a 12v/240vac mains convertor?
    I am also guessing, as already mentioned, it is not going to be just a 1/2watt resistor!
    One with a linear DC supply would probably be much more rugged.
    Max.
     
  8. #12

    Expert

    Nov 30, 2010
    16,298
    6,808
    I love old technology. It's so flat and spread out that you can actually work on it...but, resistors almost never commit suicide. You are going to find out why this one died before you're done fixing this. Please respond with the chip number of IC3 and that 8 legged chip so we can try to see which design it is.
     
  9. ss03947

    Thread Starter New Member

    Apr 13, 2014
    9
    3
    I'm as green as grass with this electric gizmod stuff...IC3, 8 legged chip, could you be more specific please.? :)

    SS.
     
  10. ss03947

    Thread Starter New Member

    Apr 13, 2014
    9
    3
    If you mean the round orange things, they look OK, all the same.

    Just noticed members locations, I'm in the UK, I'll up date my profile now.

    Thanks,

    SS.
     
  11. #12

    Expert

    Nov 30, 2010
    16,298
    6,808
    IC3 is labeled on the circuit board, right next to the burnt resistor. Try to read the printing on its flat side.

    The 8 legged chip is on the other side of the transformers. Little black guy, 8 legs. Try to read the printing on it.

    and the bulgy capacitor is that big sucker, way opposite corner from the burnt resistor.
     
  12. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,548
    2,373
    Guessed that right off the bat, Caravan was the give away.;)
    Max.
     
  13. ss03947

    Thread Starter New Member

    Apr 13, 2014
    9
    3
    [​IMG]


    [​IMG]


    [​IMG]

    SS.
     
  14. #12

    Expert

    Nov 30, 2010
    16,298
    6,808
    Like this?
     
  15. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,548
    2,373
    At one point I attempted to repair a few defunct PC power supplies and other switching supplies, I quickly came to the conclusion that many of the problems were shorted turns in the switching transformers.
    Max.
     
  16. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,986
    745
    Tlc431 is a variable zener diode, you alter the two resistors on its gate to vary the voltage,the resistor (R17) that is burnt out does it connect to the pins on the Tlc431,if so it can be worked out by replacing it with a variable one.
     
    Last edited: Apr 14, 2014
  17. ss03947

    Thread Starter New Member

    Apr 13, 2014
    9
    3
    Hi DD, I've taken a couple of photos (front & back) held against the light for you to see, it looks to me that one leg is connected, I could be wrong, you'll know better than me.

    Cheers,

    SS.

    [​IMG]


    [​IMG]
     
  18. MrChips

    Moderator

    Oct 2, 2009
    12,442
    3,361
    Nice photos always help with remote trouble shooting.

    As others have said before, the large black cylindrical capacitor labelled 150μF 400V is bulging and must be replaced.
     
  19. ss03947

    Thread Starter New Member

    Apr 13, 2014
    9
    3
    OK...Thanks for that, I've found one on the bay of plenty 321338292331, looks the same, am I right.?

    Thanks,

    SS.
     
  20. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,986
    745
    good, looks like R17 is the Anode return path for the LM431, need to know where the track goes to from the LM431 can you post more photos of both sides of the pcb, i think it will go to an opto-coupler, in which case its possible that both the opto and the LM431 have blown.


    its possibly similar to this psu design, where U5 is (your IC3,) and (your R17) is the R53.

    PS
    what is the model of the battery charger, maybe we can get a circuit from google.
     
    Last edited: Apr 14, 2014
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