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Oven wiring question

Discussion in 'Troubleshooting and Repair' started by dm295, Dec 19, 2012.

  1. dm295

    dm295

    1
    0
    Dec 19, 2012
    I have a whirlpool oven where the oven and broiler are controlled by a circuit board. The broiler works but the oven portion does not. I replaced the oven igniter thinking that was the problem. The line from the board marked broiler is hot but i can not detect any voltage from the oven side. When the oven cycle is activated it starts the timer but the igniter never heats up. I don't have the know how to trouble shoot the board. Can i take the line from the broiler and split it with an external switch and route it back to the oven/broiler sides so that i can choose which circuit receives the power? I am assuming that the oven sensor and timer is shared by both.
     
  2. quantumtangles

    quantumtangles

    152
    3
    Dec 19, 2012
    Oven Circuit Board

    Do be careful. I suggest getting hold of a certified electrician, but failing that, if you can safely fix it yourself, a photo of the circuit board and a schematic would be helpful. If it is a gas oven (you used the word 'igniter'), be really careful. You could be committing a criminal offense in your jurisdiction by attempting to repair a gas appliance without proper certification. I would strongly urge you not to try and repair it. It really is far too dangerous for anyone other than a certified professional.

    Check the fuses, including any that may be on or near the circuit board. Assuming they are ok, is the heating element actually working or is it really a case of no power being supplied to the heating element?

    If it is a fan oven, there may be a circuit breaker that kicks in when the fan stops working. Does a fan come on when the oven is supposed to be working? If not, you may have to get a replacement oven fan from espares, disconnect the mains, remove the back of the oven and remove the panel inside the front oven. Then just follow the espares video tutorial to replace the oven fan. Polarity of the (unearthed) two AC connections to the fan is not, so to speak, 'critical', but make sure the fan is turning in the correct direction when you replace it

    Is the correct DC power getting to the circuit board from the AC connection? If so, ensure the power is entirely disconnected and check the capacitors.

    Electrolytic capacitors sometimes fail because they have a limited operational life. They are the cylindrical components on the circuit board, and are always marked both with their upper voltage limit (above which they fail) and also the charge they hold in micro-farads (uF). For example, a capacitor marked as 50v 1000uF means it has a 50 volt ceiling and holds 1000 micro-farads of charge. They come in all sorts of voltage and charge configurations and are essentially temporary little batteries. They are like Swiss rolls made from a metal sheet (a conductor) and a dielectric (something that does not conduct) rolled up together as a cylinder, each layer sandwiched with the other to keep the materials separated from each other.

    Look at the tops of the capacitors to see if any of them have split. They can split completely (gunge comes out) or very slightly (tops bulge into a dome shape).

    If you have suspicions about one or other of the electrolytic capacitors, remove it from the circuit board and test it or replace it (always replace with an identical capacitor).

    By identical I mean it must have the same charge capacity in farads and it must have at least the same upper voltage limit, however you can use one with a higher voltage limit (never a lower one) provided it has the same micro-farad rating.

    To test an electrolytic capacitor, remove it from the circuit board with a soldering iron, then fully discharge it by shorting the positive and negative leads with a metal screwdriver or piece of wire. Take care not to touch the terminals when you are discharging it as they can retain charge even after an appliance has been disconnected.

    Attach the red positive lead of your multimeter to the usually longer positive pin from the capacitor and the black negative testing lead to the shorter pin (you will see markings showing minus signs on the negative side of the capacitor). Set the MM at say 20k Ohms, and work up if necessary

    The cap should begin at zero ohms but slowly charge due to the power in the battery of the multimeter. If it does not charge (if the reading remains zero on a high impedance setting such as anywhere from 20 k ohms upwards) the cap is dead and must be replaced.

    I have never done this myself but I understand it is a viable way to test caps. Personally, I would order a replacement set of all the electrolytic capacitors from Ebay, and just replace them all, because if one has failed, the others will soon follow.

    Electrolytic capacitors are often the culprit, but not always. You must remember to observe their polarity as well (put them back in the same way round they came out...as they have positive and negative pins that have to be the right way round when they go back into the circuit board.

    If the caps are fine, it is something more exotic and may require a more refined approach to identify it.
     
    Last edited: Dec 19, 2012
  3. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,186
    2,692
    Jan 21, 2010
    Quantumtangles gives some general good advice, but there is perhaps a little more to add:

    1) The capacitor may have a temperature rating. If 105C (or other than 85C) is printed on it, then you'll need to replace it with a similarly temperature rated cap.

    2) Once the capacitors are soldered into a board the wires are cit, so one will likely be no longer than the other. Go by the markings on the cap.

    3) The test with the multimeter is not reliable. Many multimeters can measure capacitance these days, but there is another more important (in many cases) measure and that is ESR. To test that you need an ESR meter. Best bet is to replace all electrolytic capacitors that don't look right, and their friends.

    4) Buying from eBay is probably not the best option.

    5) pictures would be great before you start removing components. With experience, you can spot quite a lot of stuff. Images of both sides of the board taken using natural light (not flash) are required. Make sure they're sharp enough to read markings on the components.
     
  4. quantumtangles

    quantumtangles

    152
    3
    Dec 19, 2012
    Oops. Seemed feasible. I always replace them.

    An Equivalent Series Resistance meter would be ideal but they can be expensive unless you make your own...like the engineer in the following video.

     
  5. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,186
    2,692
    Jan 21, 2010
    These days ESR's of well under 1 ohm are very common (and are the ones that are most likely to be under stress) so you really need an ESR meter that expands the scale at the low end.
     
    Last edited: Dec 20, 2012
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