When you're working on an appliance that's DOA (no lights, no response from the UI), your first troubleshooting priority is to identify where the power supply is missing.

Is it just the UI that's not getting power? Or is the main control board not getting power? Is there even power at the outlet it's plugged into?

These are the questions you need to answer before anything else, and you're going to answer these questions by taking measurements with your meter. However, there are right and wrong ways to go about this.

In this video, we're going to explore a real service call and analyze the troubleshooting techniques the tech used and figure out how he can structure his call better next time. You'll have to watch it to find out exactly how the call went down, and what the problem turned out to be, but let's go through the four mistakes that were made in the initial troubleshoot:

1. Following dummy directions. Dummy directions, for those not in the know, are when the tech sheet or service manual walks you through step-by-step how to troubleshoot a problem. These directions, if you follow them, will almost always lead you astray, have you do stupid, meaningless tests, and tell you to replace parts that aren't necessarily the problem. They can have their uses, though, as we explain in the video.

2. Making pointless ohms tests. Ohms testing has its place, but the situations where an ohms test is the best or most informative test to do are very rare. And when you're looking for a missing power supply, voltage is the name of the game. Don't check a wire harness for continuity when you can just see if you have voltage where you're supposed to.

3. Not using a loading/LoZ meter for voltage tests. Following on the previous point, even when you're doing a voltage measurement, there are right and wrong ways to go about it. When you're measuring AC voltage, you should always use a loading meter or the loading function of your multimeter. That's the only way to consistently get meaningful results and avoid getting confused by ghost voltage.

4. Not understanding series and parallel circuits. In order to understand a component's power supply, you have to understand the entire circuit it's a part of. That means identifying which components are a part of that circuit, and which are a part of a different circuit. In other words, which are in series with it, and which are in parallel.

If you want to learn how to avoid these mistakes, watch the full video below. It's taken from one of our Live Dojo workshops, which we hold on Zoom every other week. Click here to see our calendar and sign up for the next one.

Want to step up your troubleshooting game? Click here to enroll in the Core Appliance Repair Training course over at the Master Samurai Tech Academy.