Off the shelf small project and I've blown something

Discussion in 'General Electronics Chat' started by chi11i, Nov 16, 2008.

  1. chi11i

    Thread Starter New Member

    Nov 16, 2008
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    Hopefully I am allowed to ask such a basic Q on this forum.

    I bought an off the shelf electronic project that allows me to connect a houseplant to twitter - one of these http://www.botanicalls.com/kits/

    I'm new to electronics of course, built the circuit plugged it in and it worked for about 2 mins, then ceased. After head scratching i realised i had used a US AC/DC apadter (input 120v 60Hz output 6v DC 300mA) in a UK socket (240v).

    Ok - I know that was very silly of me. I've tried a UK adapter but alas I've blown something. Looking at the components used in the circiut here: http://www.botanicalls.com/kits/getting-started/ would anyone know where i should begin in swapping peices?

    Sorry for such a newbie post, if there's a more appropriate forum somewhere I'd be happy to be advised on where to ask.

    Thank you
     
  2. hgmjr

    Moderator

    Jan 28, 2005
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    Can you take a closeup digital picture of the component side of the board so that we can see if there are any visual signs of component failure? Make sure that the focus is as good as it can be.

    hgmjr
     
  3. steveb

    Senior Member

    Jul 3, 2008
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    Are you sure you want to fix it? I bought my kids cell phones, and now they only call me when they need money. What if your plants start asking for more than just water? :)

    Seriously though, is there any chance of getting a schematic of the circuit? Probably difficult, but that would really help.
     
    Last edited: Nov 16, 2008
  4. studiot

    AAC Fanatic!

    Nov 9, 2007
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    Did you solder or plug the microprocessor into a socket?

    If you just plugged it in, unplug it and then test the voltages available at the regulator.

    Test the reg voltages anyway.

    It is likely that the reg held the extra voltage for a while (it worked initially you say )
    but overheated.

    If the reg is now dead it may be the only failed component, and quite cheap to replace.

    If it is still working the project is probably beyond economic recovery.
     
  5. chi11i

    Thread Starter New Member

    Nov 16, 2008
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    Hi - I'm waiting for the company to send me a schematic - but im not holding much hope. I have a large image ill upload shortly. I've checked quite closely under a mag glass and i cant see any obvious burned out components, so i doubt they'd show up on an image - but i am very much a newb at this.

    I plugged the microprocessor in - not soldered - and I didnt have it plugged in when i soldered the base onto the board.

    It did work initially - for about 3-4 mins then died.
     
  6. studiot

    AAC Fanatic!

    Nov 9, 2007
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    So what about the tests I suggested?
     
  7. chi11i

    Thread Starter New Member

    Nov 16, 2008
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    I'm off to buy a test meter this lunchtime - i don't have one so couldn't test last night.
     
  8. chi11i

    Thread Starter New Member

    Nov 16, 2008
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  9. hgmjr

    Moderator

    Jan 28, 2005
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    Nice pic.

    I don't see anything that looks visually damaged. Once you have performed the tests at studiot's suggestion then report back with your readings and we will comment accordingly.

    Hopefully all that has been damaged will be the 120VAC wall-wart and that all you need to do is replace it with a 240VAC version.

    hgmjr
     
  10. mik3

    Senior Member

    Feb 4, 2008
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    As i can see from the parts site, the AC/DC adaptor is of the unregulated type. Thus, if you use it in a 120VAC supply, for 6VDC output the peak value of the output voltage at no load is about 9V. This is no problem for the regulator because its maximum input voltage is 15V. If you plug the adaptor into a 240CVAC then the output maximum voltage doubles and it will exceed 15V and thus destroy the regulator. Thus the regulator is 90% damaged, if you replace it the circuit may work if the uC is not damaged.
     
  11. AlexR

    Well-Known Member

    Jan 16, 2008
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    The black blob (maybe transistor or low power voltage reg) to the left of the RESET button looks a somewhat charred to me. Also the left end of the 10K resistor looks is if it has been hot at some time, probably the heat came from the charred blob!
     
  12. studiot

    AAC Fanatic!

    Nov 9, 2007
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    Presumably the 2N2222 transistor is used as some kind of output device.

    It may also have overheated, but again is worth replacing.

    Post the reg measurements when you have them and we can suggest some further tests on the transistor.
     
  13. mik3

    Senior Member

    Feb 4, 2008
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    AlexR, your right. I see a crack on the black transistor on the left side of the reset button (according to the photo) which is likely caused by overheating.
     
  14. steveb

    Senior Member

    Jul 3, 2008
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    That is a good possibility. I looked at the assembly pictures and it appears that the regulator is not mounted to a heat sink. A doubling of voltage would result in almost 4 times more power dissipation on the regulator (6V-3.3V versus 12V-3.3V). Given that the circuit worked for about 4 min. Thermal stress combined with excessive voltage seems likely. The lack of visible signs of overheating on the PCB near the regulator indicates that the current draw was not excessive and thermal stress alone may not be the only cause.

    It would seem that the regulator should be the primary failure beause otherwise it would have protected the rest of the circuit, with the exception of any input capacitors (if they are there).
     
  15. chi11i

    Thread Starter New Member

    Nov 16, 2008
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    Thanks everyone - this is all so new to me - but i'm learning! i tried the meter i borrowed last night but im still learning how to read what the outputs mean. i will post them tonight. but yes i can see the transistor looks like its burned. so given im going to need to replace at least the regulator, transistor, one resisitor and maybe the micro-processor, where is a good place to purchase online? there's a maplin near my work, but they were less than helpful yesterday.

    i also bought a new transformer - they recommended a regulated multi volt with 300mA - which either isnt working (no power from it at all last night) or is designed for some non domestic use?
     
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