Can this be repaired?

Discussion in 'General Electronics Chat' started by bowlingo, Jul 23, 2011.

  1. bowlingo

    Thread Starter Member

    Jun 29, 2011
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    Hi all,

    I have an 8 input 8 output SMS controller that I got the other day (expensive) I got it all configured spot on then I decided to short out one of the outputs (output 1) of which made a cracking noise. Now the output is staying permanantly on.


    I am wondering if this is repairable as of the below pictures (see red arrow going to component with hole in)
    the component thats blown is labelled J3Y of which might be a transistor?


    I am not sure if these kinds of boards can be hand soldered or even if its possible to get a replacement component with the limited amount of info i.e J3Y and no circuit diagram etc

    The controller is a RTU5011, 8 input, 8 output SMS controller made by the Chinese company King Pigeon

    The other relay controlable outputs seem to work fine still its just output 1 (the rest are 0,2,3,4,5,6,7)

    I need all 8 outputs to do with it what I have planned.

    Thanks

    [​IMG]

    [​IMG]

    [​IMG]
     
  2. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    You just learned rule number one of troubleshooting

    If it is working - DON'T mess around with it. :)

    That should be easily repaired(if you can find a proper replacement part) by anyone with some skill with a soldering iron. I'm leaving to pick up the wife from work and go into town for the privilege of seeing her spend my money. I'm sure someone here will know what the proper replacement is for that part.

    Do you have a schematic for it? Have you tried to google for the schematic, or for a part with those markings?
     
  3. praondevou

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    Jul 9, 2011
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    Last edited: Jul 23, 2011
  4. bowlingo

    Thread Starter Member

    Jun 29, 2011
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    Hi Kermit,

    I dont have a diagram for it nor can I find one on the net..

    The reason it went pop is I set my multimeter to the wrong range...think it was in amps then tried to measure between + and output 1....I have punched myself in the face many times :)
     
  5. praondevou

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    Jul 9, 2011
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    A simple search on newark gives the following results : newark

    Take the main specs, like collector-emitter voltage, collector continous current, DC-gain, type it into digikey or newark to narrow your results
     
  6. SgtWookie

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  7. bowlingo

    Thread Starter Member

    Jun 29, 2011
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    My problem is I do not know much about electronics apart from some basic components and how to use soldering iron etc...

    Im really looking for a direct link to possibly buying one of them then ill take it from there and see if it works..

    It might not be only that coponent that has blown due to my lack of knowledge im wondering if a transistor would normally only blow in the above situation (12v short?)

    Thanks
     
  8. praondevou

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    Jul 9, 2011
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    I my other post I sent you links. You can buy replacement transistors from newark or digikey. that's a simple npn small signal transistor, any of the transistors from the search at newark will do the job. both have the original transistor in their list but they are not available from these suppliers.
     
    Last edited: Jul 23, 2011
  9. tom66

    Senior Member

    May 9, 2009
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    Possibly.

    They look like N channel MOSFETs. Especially hinted towards due to the common failure mode of MOSFETs, to fail shorted. (Conducting, always on.)

    J3Y brings up NPN transistor - seems more likely to be an N-channel MOSFET, but it could be an NPN.

    You should be able to replace it with any N-ch MOSFET with the correct pin out. You will need a steady hand and a good soldering iron (not a $10 RadioShack.)

    [oops, late post.]
     
  10. bowlingo

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    Jun 29, 2011
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  11. praondevou

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  12. Kermit2

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    Feb 5, 2010
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    Removing components is often much harder than soldering in new ones.

    I suggest you prepare buy getting some 'solder wick'. This is simply fine copper wire braided into a linear weave and often treated with a small amount of soldering resin to aid in getting the solder to flow. You place it on top of the place you want to remove solder from and then press a soldering iron on top of that until you see the solder 'soak' into the braided copper.

    Since the SMD device is already shattered, I would suggest using a small set of wire cutters and trying to snip out the plastic portion of the device. Getting it out of the way will allow you to remove each leg individually without the other portions holding down the leg you are trying to desolder. Be very careful doing this, you do not want to damage the copper traces. Another method is to use a dental pick and try to pry up the small legs one at a time as you heat them up. I've had good luck with both methods, but I use the one I think will do the least damage to the board.
     
  13. bowlingo

    Thread Starter Member

    Jun 29, 2011
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    Thanks Kermit..

    I think desoldering and resoldering this component is going to be a bit to advanced for me...im an electrican who has done a bit of soldering and when I was much younger 25 years ago or so I made a few kits etc.

    My dad would be more than capable of soldering this but his eye sight is in a bad way and although he would willingly have a go at it I dont think its a good idea due to the cost of the unit.

    I think the way forward is to first get the component then possibly contact an electronics company in my area..there is one about 20 miles away from me who im pretty sure would solder it for me if I gave them the part.

    What I need to do now is source the exact part as although ive had lots of people telling me what the equivalents are etc I really need to some how make sure the transistor I get is 100% correct.

    Does it make sense that when you short out a unit like this it would blow a transistor and a transistor only (popping sound) and when blown it would stay on?

    Thanks
     
  14. praondevou

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    Yes, it's possible, that only the transistor has a short and yes it's possible that there is more blown, without a schematic or someone who has a look at the unit to see where traces are going and what could be the circuit, you can't really say.

    Since the transistor is already blown it can't get worse if you put an equivalent transistor in it as we suggested. Worst case, this blows too, even though that's not likely. Otherwise you'll have to try finding the original part from some chinese supplier, but the suppliers I've seen do not list prices online, so you may have to contact them one by one.
     
  15. JimG

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    Dec 7, 2009
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    I can understand being hesitant to mess around with an expensive board. But removing that transistor would be a piece of cake with some thin, pre-fluxed solder wick and a fairly small tipped iron.

    Once off, use the wick to clean off any globs of old solder from the pads (leave them alone if there is just a flat "tinning" layer left). Be careful to not allow the wick to "freeze" to a pad or you could pull off the pad.

    Dab a little flux on the pads, place the new NPN, hold it down with something pointy. Tin your iron and touch it to the end of one of the pins. That will tack down the pin.

    Go to the other two pins and "push" solder into the ends of the pins. Go back to the first one and do the same.

    This sounds complicated, but in practice this is a pretty easy SMD to hand solder.

    Jim
     
  16. THE_RB

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    I remove SOT-23 in 3 or 4 seconds, with a medium sized tip;

    Heat the single leg quite hot and apply extra solder to it (thermal mass keeps it hot) then before it cools put the tip sideways across both of the other legs with lots of solder on the tip, the whole transistor will come straight off (full melt 3 legs) and stick to the solder on the tip, then flick the dead transistor in the trash with the excess solder.

    It sounds rough but is better then other methods due to the speed, there is less chance to damage the board as the board is headed for such a small time. I don't turn the iron up, just the usual soldering temp is fine.
     
    Last edited: Jul 25, 2011
  17. KJ6EAD

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  18. radiohead

    Active Member

    May 28, 2009
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    Get a circuit board from a scrap pile. Practice desoldering components on that before you commit to possibly damaging your board further.

    The more you practice soldering/desoldering, the better you will be at it. There are four main ways to desolder.

    The most preferable would be the use of a desoldering iron
    The next would be the use of desoldering wick
    The next would be a solder sucker
    and the last and probably the least preferable would be to heat the solder to its melting point, then quickly giving the board a sharp rap on a bench or table, if the solder is still in its liquid form, it the shock should dislodge most of it.
     
  19. bowlingo

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    Jun 29, 2011
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    I took it to a local electronics repair company this morning...didnt think these places existed anymore..huge room full of kit, screens etc. The guy said he will be able to source the part needed by removing a known working transistor, testing it then ordering the replacement..he said he will also check the other components on the board as far as he can in case something else has blown as well..he said it would take a couple of days at a cost of around £50.00
     
  20. praondevou

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    Jul 9, 2011
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    Well, £50 is not much, but still a lot compared to what one would pay doing it by himself...:D Anyways, good luck.
     
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