Find the Fried component? or How to Identify the black blob

Discussion in 'The Projects Forum' started by landennick, Sep 18, 2013.

  1. landennick

    Thread Starter New Member

    Sep 18, 2013
    3
    0
    Hello all.


    I woke up this morning to a nasty smell in the kitchen. It seemed to be coming from the fridge. Now it was not a rotting sort of off thing skulking in the dark when the light goes out kind of smell, but a caustic, strip your nose out, chemical stench - a little bit like TCP (a British antiseptic).


    Upon investigation, the smell seemed to be coming from the top of the fridge (where the controls are) [Oh, Its a Bosch Logixx Easy Access KTR18PW20G if you were wondering]


    I decided to dismantle the fridge to get to the PCB (which had malfunctioned and been replaced in the past.) and sure enough there was the problem. A grey resistor like chard bit, fused to the plastic of the fridge and sitting over a blackened bit of PCB. The trouble is I can't identify the dead bit, (sad face.)


    I have found the replacement PCB listed on line as Module-489581 http://www.amazon.co.uk/Bosch-Fridge-Freezer-Module-489581/dp/B0098MDE8Q but besides the fact that they've sold, If I bought a hole new board (for £60) then I wouldn't get to do any soldering.


    So can you help me work out what the burned sausage on the PCB used to be?
    Now you've been very patient in reading this rambling request (thank you) and as a reward I have attached a PDF of the PCB with the component circled. I don’t have a photo of my dead one, no camera today, but perhaps I might sort out a picture if you need it.


    P.S. As far as I can tell the smell was mostly from the plastic of the Fridge itself which has turned black and emitted all sorts of nasty vapours into my food and has thus been banished to the garden till it calms down and I can get the control board fixed.


    Thanks for any help or advice as to what to do next. (Excluding 'buying a new fridge',) 'cause I don't have the money and it is the best fridge I've ever used so I don’t want it to die.
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,515
    2,369
    There is not much on the board, you may have to do a bit of 'reverse engineering' and trace the circuit out, it appears to be a mechanical or SSR on the end of the board itself?
    The grey resistor looking object may be identified once the circuit is drawn out?
    Max.
     
  3. #12

    Expert

    Nov 30, 2010
    16,261
    6,768
    The gray box is a dual capacitor.
    Fortunately, the board is small enough to trace out by hand.
    Poetic justice for ransoming 7 parts for 60 pounds.
     
  4. landennick

    Thread Starter New Member

    Sep 18, 2013
    3
    0
    I wish I could trace out the PCB but unfortunately it is something of an iceberg.

    Here is the Tip.
    [​IMG]
    As you can see, I have sorted out a camera and attach some pictures of the business end of the board which though not just 7 components is indeed overpriced.

    Here is bellow the water line
    [​IMG]

    It's the cityscape over on the left that gets a bit tricky.

    I've been thinking that If I can't get it to work then I should hack a raspberry pi in there. More fun for less money, and it will be a good excuse to rig up the bar-code auto inventory system that I have been dreaming of for the past decade.

    Anyway so, That stench is still drifting out of the top of the fridge though it has lessened some what and I still can't get the Bosch site ( http://www.bosch-home.co.uk/store/product/PCboard/489581 ) to let me buy a new board :mad:. Not that I've tried signing up with for an account, If it won't put the item in the cart when I click the big 'add to shopping cart' button then I'm not going to register just to see if it's a log in issue.

    This place however is full of cool projects so I recon I've found a new way swallow up evenings.

    Thanks
    Nick
     
  5. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,515
    2,369
    Even if you just trace the end where the power components are might offer a clue, no need for all the rest to the left of them?
    Max.
     
  6. #12

    Expert

    Nov 30, 2010
    16,261
    6,768
    Here's a guess: The load this thing is driving shorted and fried that component. Find the short first, then fix the driver.
     
  7. sheldons

    Active Member

    Oct 26, 2011
    616
    101
    faulty item thats failed is a fuse-possible failure will be the capacitor-the zener and the resistor -all part of the capacitive dropper which forms a simple powersupply-also if you check across the capacitor which will be directly connected to the zener for any lo ohms reading that may help localize the fault....it may be you have a faulty relay for the compressor or faulty compressor-in which case the fridge is scrap unless you are able to replace it,check the system holds a vacuum after vaccing it down to check for leaks before a regass etc....also if fitted you may have a fault with the defrost heater/timer etc
    Depending on the fault and if there is a sc after the capacitor/zener on your powersupply you may find the control ic sc if the device which switches the relay on the compressor has failed-some boards use a triac some a thyristor in which case your board is scrap.....
     
    Last edited: Sep 19, 2013
  8. landennick

    Thread Starter New Member

    Sep 18, 2013
    3
    0
    woot sheldons - so it's something along the lines of a 'Quick Blow Micro Axial PCB Mount Fuse'.

    Multimeter time then. I'll have to dig it out of.... wherever I hid it ... (Moved in last year and till working on the house, plus organization does not appear to be one of my skills I'm a noob when it comes to electronics so any hints to one who knows nothing would be much appreciated. I'll get to creating a diagram of this board and the one that fried two years ago and then I’ll give you the readings. Will that lead to a means of working out the rating of the fuse?.

    Thanks again sheldons, that is a dense post.
     
  9. sheldons

    Active Member

    Oct 26, 2011
    616
    101
    fuse rating will be on the fuse itself and should also be on the pcb.....the fuse wont be all that high a rating-for quick testing you can fit a 1 ohm fusible resistor,say 1/4 w just as a quick test after you have located the faulty components on the board....do remember also that this type of power supply is in no way mains isolated which means when connected to the mains the pcb will give you a shock if you touch the wrong things while handling it and NO connecting oscilloscopes unless you want a loud bang on switch on
     
  10. t06afre

    AAC Fanatic!

    May 11, 2009
    5,939
    1,222
    I suspect that the area that is burned is a transformer less power supply. And that the part bolted to the cooling fin is a voltage regulator. Can you see if you can find ID numbers on the latter part?
     
  11. MrChips

    Moderator

    Oct 2, 2009
    12,429
    3,360
    I would venture to guess that the burnt device is a resettable thermal fuse that simply over heated and burst into flames, something like this:

    [​IMG]

    Tracing the circuit, it looks like the molex pins are AC line input to a 1μF/275V capacitor, fuse, 100Ω resistor, diode rectifier.

    Try replacing the fuse.
     
  12. shortbus

    AAC Fanatic!

    Sep 30, 2009
    4,004
    1,525
    Fixing replacing the fuse is all and good. But it doesn't fix the problem. The OP said this board has been replaced before. More trouble shooting on the whole system seems like a good idea to me. But then, what do I know?
     
  13. t06afre

    AAC Fanatic!

    May 11, 2009
    5,939
    1,222
    Perhaps replace the whole transformer less power part on the board with small proper power module
     
  14. MrChips

    Moderator

    Oct 2, 2009
    12,429
    3,360
    The fuse is supposed to go into a high impedance state on over-current.
    Obviously the fuse failed to do its job and went on fire. That is very unusual.

    I would try replacing the fuse, perhaps with a different type of fuse.

    What are the markings on that 3-pin device on the metal heat sink?
     
Loading...