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How do I fix this "blown" pcb area?

Discussion in 'Troubleshooting and Repair' started by peterzz, Feb 9, 2014.

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  1. peterzz

    peterzz

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    Feb 9, 2014
    Hi there,

    I am trying to fix my induction stove! And I have just found the (or one of the) problem(s) with it.

    What you can see on the picture below is actually the underside of the neutral pin.
    I have found soldering fixes the pcb, but not the problem. below are more images of the pcb, what components could result in this fault? ->immediate failure when engaging power to coil (start heating on stove).


    [​IMG]
    [​IMG]

    How can I fix this?

    also, why didn't the fuse blow instead? is the thin strip part of the pcb "fuse" function material?
     
    Last edited: Feb 9, 2014
  2. peterzz

    peterzz

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    Feb 9, 2014
    empty
     
    Last edited: Feb 9, 2014
  3. davenn

    davenn Moderator

    13,866
    1,958
    Sep 5, 2009
    hi peter

    welcoem to the forums :)

    you can use some strips of tinned wired soldered across the gap

    BUT FIRSTLY
    have you determined WHY the small bit of circuit track blew like a fuse ??

    There's no point trying to repair the track until you sort the fault out

    cheers
    Dave
     
  4. peterzz

    peterzz

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    Feb 9, 2014
    Hi Dave! thank you! you were quite right, more below.
     
    Last edited: Feb 9, 2014
  5. peterzz

    peterzz

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    Feb 9, 2014
    [​IMG]
     
    Last edited: Feb 9, 2014
  6. peterzz

    peterzz

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    Feb 9, 2014
    Sooo, lets say my attempt was a succes at gaining new information.. (its a learning proces for me:)

    first thing, the stove works fine until the moment of engaging power to coil.
    second, it does not work fine after that. below result: ps. im still wondering why the pcb goes and not the fuse?

    [​IMG]

    So what should I do from here? there is no visual component failure
     
    Last edited: Feb 9, 2014
  7. jpanhalt

    jpanhalt

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    Nov 12, 2013
    What are the components on the other side?

    I have seen motor controllers with a parallel groups of devices, say solid state switches (e.g., SCR's or mosfets) show that type of board failure when one fails shorted. I can't make out the typical 3-pin pattern on the reverse side you show, and I am not even guessing that is what the components on the other side are. But, there is a chance that if you show the other side, we may have some suggestions to save the board.

    Otherwise, you could just keep soldering chunks of wire over every failure point until, eventually, the circuit fuse blows. The board still won't be working, though. ;)

    John
     
  8. peterzz

    peterzz

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    Feb 9, 2014
    Hi John.
    No exactly, it seems the board just took the now first new thin strip to blow at, so this will indeed just keep moving down the line. Unfortunately this means the location gives me no clue about what could be at fault. How and where should I start looking?

    what I do know: failure when engaging coil to start heating, immediate failure.

    overview picture of top side:
    [​IMG]
     
    Last edited: Feb 9, 2014
  9. peterzz

    peterzz

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    Feb 9, 2014
    So I know it fails when engaging top left coil, this is what connection and components look like:

    [​IMG]

    ps, I don;t know if it would fail or not if engaging bottem coil

    Does the fact that the pcb is blowing give any clues as to what could be the problem? obviously there is to much current going trough it, so maybe some current regulating part? or maybe the current which should go trough the coil finds an alternate route into the "regulation" pcb part?
     
    Last edited: Feb 9, 2014
  10. jpanhalt

    jpanhalt

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    Nov 12, 2013
    Sorry, but I do not recognize what appear to be the critical parts. Someone else may.

    As a word of caution, some of the capacitors have fairly high voltage ratings (e.g., 850V and 400V) as well as capacitances. They can give you a pretty good shock and may not be fully discharged when you remove the board, so be careful. After disconnecting the mains power to the board, you would want to use a resistor to short across the leads to discharge them. Anything rated at less than 50V won't give much of a shock.

    John
     
  11. peterzz

    peterzz

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    Feb 9, 2014
    full topside overview
    [​IMG]
     
  12. peterzz

    peterzz

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    Feb 9, 2014
    Ah thanks I was wondering if anything on there was a danger haha. I'm a Mechanical engineering student so I have some electronics knowledge but not a lot.
    the problem is I have no clue as where to search for a fault. the burnout location doesn't seem to tell anything and there are no components with visual damage.

    side of grey boxes:
    [​IMG]
     
    Last edited: Feb 9, 2014
  13. jpanhalt

    jpanhalt

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    Nov 12, 2013
    Do the black tombstones next to the inductor/transformer coil have any markings on them? They are physically close to the failure points.

    John
     
  14. peterzz

    peterzz

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    Feb 9, 2014
    picture above, I have no idea what they are, special type of capacitor?
     
  15. jpanhalt

    jpanhalt

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    Nov 12, 2013
    They look like AC capacitors. I wonder if one or both failed, which is causing the over current. Since they are at the mains input, they are probably to prevent interference from the unit getting back into the mains.

    I haven't read this article (I am cooking dinner), but the circuit shown is certainly consistent with what I see on your board.

    http://www.acoustica.org.uk/other/filter.html

    You will need to remove them to test them. Do you have access to a smaller soldering iron? Do you have solder braid to remove the solder? I hate to suggest what I do, because I will get jumped on. When I don't have solder braid (which is very rare), I melt the solder and flick the boards over a shop waste basket. That gets enough solder off to wiggle the parts -- maybe with a little more heat -- and eventually get them out without damage to the part or the board.

    John
     
  16. mursal

    mursal

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    Dec 13, 2013
    Usually if the fuse is the correct current rating and type, if it doesn't blow the problem causing the high current (probably a short between phase and neutral) is before the fuse in the circuit. Towards the input connections from the fuse.
    Did you try a Google search for a circuit diagram, it might help a little, no guarantees though.
     
  17. peterzz

    peterzz

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    Feb 9, 2014
    I tried looking for a circuit diagram, could not find it.
    As far as I can tell from pcb basically the only things before fuse are the AC capacitors John was talking about so I guess that would be a good place to start. I could probably make use of some decent soldering tools in the weekend. Any information anywhere on how I would test these?

    thanks.
     
  18. jpanhalt

    jpanhalt

    426
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    Nov 12, 2013
    Many years ago, I learned that Sutton's Law* is rarely violated. The capacitors are near the problem and can fail short, but that doesn't explain why you get failure only under load. Nevertheless, they are simple to test. That is why I mention them. If those capacitor are OK, then the problem is downstream and the PCB traces near the capacitors were only the weakest link.

    If the circuit to which I posted a link is reasonably representative for what you have, then a short test without the capacitors in circuit (after repairing the newly burnt out trace) should produce minimal harm to the "grid". I think your chance of success is relatively small, but it is not nil. Is there any way you can substitute a smaller mains fuse or maybe test the circuit in series with an incandescent light bulb to limit the current draw in the event of a short circuit?

    John



    *After Willie Sutton, a bank robber.
     
  19. duke37

    duke37

    5,364
    772
    Jan 9, 2011
    One rectangular block block is labelled CP24 so is probably a capacitor in the power section.

    The printed circuit track could be linked with a strand of thin wire. Most flexible cables are made with wire of thickness 0.0076 in or 0.2mm. This has a fusing current of about 6A so you could use this to lonk the track. What is the fuse rating fitted?

    If there is a lot of solder, I use a solder sucker to remove most of it and then use braid to clean up further. If you do not have the braid, you can use braid from coaxial cable. It needs to be free of corrosion and could be smeared with a very small of flux to aid wetting.

    I am not skilled enough to use a solder gun to get the right temperature.

    Edit
    If the circuit blows instantly presumably the power is switched before the board, not in the board.
     
    Last edited: Feb 10, 2014
  20. peterzz

    peterzz

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    Feb 9, 2014
    good question, it says T400L250V on the fuse, both numbers I assume has to do with voltage, stove can be either connected to 250 or 400 V, so dont know amps..actually topside near fuse it says fp10 T 400 MA so 400mA maybe?. Actually I am sure its not relevant but I'll ask just to check, below is how I have it connected (perilex):

    I should also add that right side is working fine (also 2 coils with same board, its just mirrored really)
    [​IMG]

    And some more on before the circuit blow.
    The induction plate, when pressing ON button first recognizes if there's a pan above the coil or not (looking for a load I believe, all functions in the same board), this worked fine, only when pressing the heat button, as opposed to on button, did it immediately fail.

    I am still trying to get my head around what John is proposing, and how this would help. I think its remove the capacitors, connect everything up, if nothing blows you know its the capacitors? but isn't there a good chance it blows because the capacitors aren't there, or it doesn't blow because its not working properly?

    I was looking for a whole new board to see if I could do an easy fix but same as circuit diagram or other parts these seem to be not available anywhere.
     
    Last edited: Feb 10, 2014
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