Troubleshooting Electrical Problems
Finding your wiring diagram
In older models, wiring diagrams may be pasted to the back of the oven. In newer machines, they may be in a plastic bag inside the console or inside one of the front legs of the oven. (Figure 3-G) In ovens with digital controls, a diagnostic sheet with oven error codes and diagnosis procedures may sometimes be found in the same places.
If you are tracing a complex electrical circuit, it may not hurt to make a couple of photocopies of the wiring diagram, so that you can physically follow different circuits with a colored highlighter pen.
Are you a “gearhead?”
I tried to write this guide to help everyone, even beginners, who wants to try to fix their own cooking appliance.
But of course, not everybody has the same skill set. Some people are VERY mechanically-savvy, and some people have very few mechanical skills and little knowledge.
So if you can read a wiring diagram and use a Multimeter, you can probably skip the rest of this page.
How to use a Multimeter
Many home handymen are intimidated by electricity. It’s true that diagnosing and repairing electrical circuits requires a bit more care than most operations, due to the danger of getting shocked. But there is no mystery or voodoo about the things we’ll be doing. Just remember this simple rule:
While you are working on a circuit, energize the circuit only long enough to perform whatever test you’re performing, then remember to take the power back off it to perform the repair.
You don’t need to be concerned with any theory, like what an ohm is, or what a volt is. You will only need to be able to set the Multimeter onto the right scale, touch the test leads to the right place and read the meter.
In using the Multimeter for our purposes, the two test leads are always plugged into the “+” and “-” holes on the meter. (Some Multimeters have more than two holes.)
Set the dial of the VOM on the lowest VAC scale (A.C. Voltage) over 120 volts. For example, if there’s a 50 setting and a 250 setting on the VAC dial, use the 250 scale, because 250 is the lowest setting over 120 volts.
If you’re testing 220 volt circuits, use the lowest scale over 220 volts.
Touch the two test leads to the two metal contacts of a live power source, like a wall outlet or the terminals of the motor that you’re testing for voltage. (Do not jam the test leads into a wall outlet!) If you are getting power through the VOM, the meter will jump up and steady on a reading. You may have to convert the scale in your head. For example, if you’re using the 250 volt dial setting and the meter has a “25” scale, simply divide by 10; 120 volts would be “12” on the meter.
Don’t let the word “continuity” scare you. It’s derived from the word “continuous.” In an electrical circuit, electricity has to flow from a power source back to that power source. If there is any break in the circuit, it is not continuous, and it has no continuity. “Good” continuity means that there is no break in the circuit.
For example, if you were testing an ignitor to see if it was burned out, you would try putting a small amount of power through the ignitor. If it was burned out, there would be a break in the circuit, the electricity wouldn’t flow, and your meter would show no continuity.
That is what the resistance part of your VOM does; it provides a small electrical current (using batteries within the VOM) and measures how fast the current is flowing.
For our purposes, it doesn’t matter how fast the current is flowing; only that there is current flow.
To use your VOM to test continuity, set the dial on (resistance) R x 1, or whatever the lowest setting is. Touch the metal parts of the test leads together and read the meter. It should peg the meter all the way on the right side of the scale, towards “0” on the meter’s “resistance” or “ohms” scale. If the meter does not read zero ohms, adjust the thumbwheel on the front of the VOM until it does read zero. If you cannot get the meter to read zero, the battery in the VOM is low; replace it.
If you are testing, say, an ignitor, first make sure that the burner leads are not connected to anything, especially a power source. If the ignitor’s leads are still connected to something, you may get a reading through that something. If there is still live power on the item you’re testing for continuity, you will burn out your VOM instantly and possibly shock yourself.
Touch the two test leads to the two bare wire ends or terminals of the ignitor. You can touch the ends of the wires and test leads with your hands if necessary to get better contact. The voltage that the VOM batteries put out is very low, and you will not be shocked.
If there is NO continuity, the meter won’t move. If there is GOOD continuity, the meter will move toward the right side of the scale and steady on a reading. This is the resistance reading and it doesn’t concern us; we only care that we show good continuity. If the meter moves only very little and stays towards the left side of the scale, that’s BAD continuity; the ignitor is no good.
If you are testing a switch, you will show little or no resistance (good continuity) when the switch is closed, and NO continuity when the switch is open. If you do not, the switch is bad.
How to read a wiring diagram
Sometimes you need to read a wiring diagram, to make sure you are not forgetting to check something. Sometimes you just need to find out what color wire to look for to test a component. It is ESPECIALLY important in diagnosing self-cleaning ovens.
First, find your wiring diagram as described above.
Each component should be labelled clearly on your diagram. Look at figure 2-F. The symbols used to represent each component are pretty universal.
A few notes about reading a wiring diagram:
Wire colors are abbreviated and shown next to each wire. For example, Y means a yellow wire, PK means pink, R means red. Black is usually abbreviated BK, blue is usually BU. GR or GN are green, GY is gray.
A wire color with a dash or a slash means — with a — stripe. For example BU-W means blue with a white stripe, T/R means tan with a red stripe.
Notice that in some parts of the diagram, the lines are inside a dashed box. These switches and wiring are inside of the timer or other block of switches. In some wiring diagrams, wiring and switches inside a timer or other switchblocks are drawn with lines that are thicker than the rest of the wiring.
The small white circles all over the diagram are terminals. These are places where you can disconnect the wire from the component for testing purposes. The small black circles indicate places where one wire is connected to the other. If two wires cross on the diagram without a black dot, they are not connected.
Switches may be numbered or lettered. Usually the terminals on the outside of the timer or switch are stamped or printed with markings that you will see on the wiring diagram.
To test a switch, mark and disconnect all the wires. Connect your ohmmeter to the two terminal leads of the switch you want to test. For example, in figure 2-F, if you want to test the door switch, take power off the machine, disconnect the wires from it and connect one test lead to COM and one to NC. Then flick the switch back and forth. It should close and open. If it does, you know that contact inside the switch is good.
Remember that for something to be energized, it must make a complete electrical circuit. You must be able to trace the path that the electricity will take, FROM the wall outlet back TO the wall outlet. This includes not only the component that you suspect, but all switches leading to it, and sometimes other components, too.