Most home appliances take AC voltage, supplied to your house from the utility company, and use it to make heat, light, turn a motor or, commonly, all three at the same time. But when the appliance stops functioning, a logical approach to troubleshooting comes in handy. The most common problems with household appliances are mechanical in nature: a broken or worn out component (such as a switch or motor), a loose wire, or a bad connection.
Troubleshooting appliances comes down to checking for proper voltage at each circuit component, typically 110 to 120 volts AC, as well as checking the integrity of components and connections using functions found on Amprobe multimeters.
Step by Step Troubleshooting:
1. Check the AC supply voltage:
To measure the AC supply voltage at a receptacle, first set the DMM (digital multimeter) function switch to ac volts and, if using a manual ranging model, select a range greater than the voltage you expect to measure (greater than 120 volts). If using an auto-ranging meter, the meter will automatically select the most appropriate range. Next, connect the test leads to the volts input and common jacks on the meter.
Carefully, insert one probe of the DMM in one slot of the receptacle, and the other probe in the other slot of the receptacle. You should read about 120 volts. The power cord from the appliance usually has three wires going to the plug: black, white, and green. Black is usually the “hot” wire, white is usually “neutral”, and the green wire should be ground.
If you measure no voltage, check to make sure the circuit breaker or switch controlling the receptacle is ON. If voltage is detected at the receptacle, you could have a problem in the power cord. That will be your next test.
2. Check The Power Cord:
Over time, and sometimes through accidents or flexing, the internal conductor in the power cord can break while appearing perfectly normal on the outside. To check a power cord, first disconnect it from the outlet. For this next part, you will need to gain access to the internal connections on your appliance.
Set your DMM to the resistance or “Ohms” function and measure the resistance between each prong of the plug and the point where the power cord connects to the appliance. The flat, narrow blade on the plug should be connected to the black wire. The flat, wide blade goes to the white wire. The round pin connects to the green wire.
A good power cord will have less than one ohm of resistance from the plug to the end of each wire. Anything higher than one ohm may indicate a cord that is starting to break down and could become overheated when in use. Replace the entire power cord if any wire shows high resistance or “OL” is displayed on the meter.
3. Check the Current Draw:
Current draw is measured in one of two ways: using a clamp accessory attached to your DMM, or using a clamp meter.
To make a current measurement with a clamp accessory, insert the clamp leads into the current jack and common jack of the DMM, and set the DMM to the AC mA range. Clamp the jaw around one conductor (wire) of the circuit to be measured. The current clamp will act as a step down transformer, taking the higher current consumed by the appliance and transferring it to a much smaller current (usually 1000 to 1) which the DMM can handle. Be careful not to clamp the jaw around both conductors, this will cancel the signal showing zero current.
To make a current measurement with a clamp meter, select the AC current function and clamp the jaws around one conductor. The display will show the current being measured.
4. Checking Switches:
You can check switches in a couple of ways. If the appliance is plugged in, you can check both the input side and output side of the switch for voltage.
With the leads plugged into the volts and common inputs, set the DMM to the AC voltage function. Touch one probe to ground (the metal frame of the appliance) or to the neutral connector on the power cord (the white wire). Carefully touch the other probe to the connectors on the switch, first one side, then the other. With the switch in the “ON” position, the voltage should be present on both input and output lugs.
Another way is to check the continuity through the switch. For this test, remove power from the switch first by unplugging the appliance.
Next, isolate the switch by removing the wire or wires from one side of the switch.
Then, set the DMM to the continuity function and place one lead of DMM on the input lug of the switch and the other lead on the output lug of the switch. When the switch is on, the DMM should sound the audible continuity signal and read about zero ohms. With the switch in the off position, the audible tone should stop and the DMM will display “OL.” If it doesn’t, you have found your problem; a defective switch.
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