Troubleshooting Techniques: Using a Multimeter | Tech, No Babel

Transcript: Previously, we talked all about making invisible things visible. One good way to do that is if you’re shooting IR out of a remote, for example, you’re not sure if it’s good, you can simply use your smartphone camera. There are other cables that you can use to illuminate, if you have electricity, but how about if you know you’ve got electricity but you don’t know if you’ve got enough electricity? How do you deal with that? Well, you use a multimeter. I’ve got one here. This is a really cheap one. If you’re just getting started, I’m not sure to the accuracy of these things, but they’re very inexpensive over at Harbor Freight, so you can pick one up there. Let’s take a look at all the functions.
Here we have it, and first let me turn it on, and you’ll notice we’ve got all zeros. Occasionally, it bounces a little bit. The first thing that I want to do is give you just a little tour here. We have DCV, that’s DC voltage. Then we have ACV, AC voltage. DC amperage over here. Then we’ve got something right here, if we wanted to test diodes, and then resistance over here with the ohms symbol, which is a Greek letter Omega. Basically in this style multimeter and there are auto ranging multimeters that automatically show you how much you have, even if you don’t check the range yourself.
In this case, I’m going to be testing a 9 volt battery. This is just a cheap 9 volt battery that I picked up at the Dollar Store actually, and so I moved it to 20. That gives me the range of 10 to 20 volts. Something like that. What I’m going to do is take that, take my probes which are these little [dual head 00:02:16] keys here. Black is negative, so I’m going to touch to that guy. Red is positive, so I’m going to touch it there. You’ll see that we have 9., 9, 8, so in the 9 volt range. That tells me that this battery is, in fact, good. That’s one of the things you can test.
Another great thing that you can test by using the resistance or the ohms setting is you can test if you’ve got continuity. Now there are some meters, I’ve used a much nicer meter when I was in tech support that had a little buzzer that you could use to test continuity with, but I found that this works perfectly well, and that is, just touching those together you can see that there’s no resistance or very little resistance between these two probes. If I had a piece of wire and I wasn’t sure if an electrical signal was getting from point A to point B, if I’ve got this one point, etc., on it, then that tells me something’s wrong. Because I put a probe on one end and a probe on the other and it still says that, I’ve got a short.
If, on the other hand, it’s showing me a number, that tells me that in fact electricity is able to get through there, but there’s something else that it can also tell me. It can also tell me that while electricity can get through there, maybe there’s a lot more resistance than you would think, so that’s something else for you to consider is you can with this particular set of tests, you can test how much electricity is going through your system. You can test how much resistance you have in a piece, whether it’s too much, too little, etc., or by going through to this setting, the DC amperage, and typically we’re going to be in DC when we’re doing testing on electronics.
What comes out of the wall is AC, but as soon as it reaches a power supply, most of the time it’s switched over to DC for electronic pieces and parts, not always, but most of the time, so most of the time they’re going to be on DC, so you can also check the amperage. If you have a power supply that says it’s 1 amp power supply under load, you plug that in. In order to do that test, you’ll have to split one of the wires and put these 2 probes in line. Though that’s something else for you to consider is, you would have to do the test a little bit differently, so in line on the negative side or in line on the positive side, and that will also allow you to do that test to see if you’re, maybe you’re getting enough volts, maybe the resistance isn’t too great, but you’re not getting enough amperage, so that can also cause the problem that you’re seeing.
That’s a really, really basic overview of the multimeter. The multimeter is capable of a lot more. I’m not saying I’m an expert. I’m just saying sometimes looking the battery isn’t the right test. Sometimes using a multimeter is.