Archive for the ‘Electronics Repair’ category

How to manually check electrical wires for polarity.

August 1, 2010

Multimeters can be confusing and scary for first timers. That pretty much goes for anything you use for the first time, I suppose. But you may get scared away by all the symbols and meanings and different configurations that are on multimeters, if you’ve never used one before.

But how did you learn to drive? You had to learn all the traffic symbols and rules before you successfully hit the road. Same deal here. Crack the encryption and begin to learn the language and you’ll wonder how anyone could be scared of this wonderful little tool.

So I hope to begin writing some basics of using a Digital Multimeter blog on here as well. Probably giving it another category such as Tutorials/Walkthroughs or something of the like.

In this blog I’d like to just give one or two quick basics to handling and reading a Digital Multimeter. Something quick and direct for the first timers, as I myself once was.

The following will be a walkthrough on how to check the polarity of circuits (wiring) with a Digital Multimeter. I can only walk you through Digital Multimeters because I’ve never used an Analog Multimeter (I’m so nu skool!).

Okay, so the first step to doing anything with electrical devices or electrical circuits is to take those saftey precautions. Don’t electricute yourself or damage your home appliances because you got bored and wanted to see the voltage of your microwave. Please follow all saftey rules in your Digital Multimeter’s manual, or the ones you found online. I’m no where near responsible for anyone’s mistakes, proceed with caution and at your own risk!

The first thing to know about Multimeters is that they are just as fragile as the circuits you are testing them on. Don’t test a little cheapie multimeter on something that’s drawing in 100 amps of electricty and set it to 10 amps. It will fry your multimeter and then break and maybe even cause damage to you. Know your Multimeters limitations and play by them.


Today we will be testing wiring for polarity. What does that mean?

It means that the wires were not marked or there is absolutely no indication which wire is Positive (+) and which wire is Negative (-). This will be essential to know the correct polarity if you are testing circuits and devices to ensure that the device is working correctly or not. Or if you must go in and rewire or something, you must know the correct polarity or the device will not work when you are finished repairing it. Today’s wiring is indication somehow someway by the negative wire having somekind of indication on it. But as I stated before, this is just a simple test for someone to get used to using a Multimeter.

Pretty simple.

So turn on your Digital Multimeter and connect the Negative (-) lead to the COM port. Then connect the Positive (+) lead to the V/mA port. Make sure to set your settings to the next highest rating of voltage. For this example, since I’m testing the wiring of a 1.5v DC wire, set the DCV to 20V.  I set it this way because it’s the lowest setting of that range on my Multimeter that I’m using.

Then simply touch your Positive and Negative leads to the wire. You will get a numerical reading regardless of the polarity. But the point of this exercise is to make sure we know the polarity of the wires. If you see a Negative (-) sign flashing before the numerical value, you are recieving a “negative” reading. This means your leads are in the incorrect polarity positions on the circuit (wires). Switch the leads to the opposite wires. You should get the same numerical reading, just without the flashing negative signal before them. You have corrected the polarity, and the multimeter’s leads are attatched to the correct polarity. This means that whatever wire the Postive (+) lead is connecting to at this point, is a Positive wire. The lead connecting to the other wire is telling you, the wire is negative.

The simplist version of this test is for speaker wire. If the polarity is reversed, the sound output to the speakers will be noticable. If the polarity is correct, the sound will be normal. Once again, if you reverse the polarity on your speakers, no harm will be done, it will just sound bad. Simply reverse the polarity to regain proper sound.


How to read Universal AC Adapter schematics

July 20, 2010

I’m currently involved in a project to power small electronic devices without batteries. I’m using a universal AC Adapter that I bought cheap and modified the adapta plug on.

I was modding the adapta plug to power a small cassette player and now mp3 player for the home. Before I did this, I needed to know about the connection rules so I wouldn’t fry my equipment.

I went out and bought the adapter and forgot how to read polarity schematics. So I went online to review, and figured I could write it down here for future references. So when I become super lazy, I only have to log into my own WordPress page to find it.

Find the diagram that shows three circles connected by lines. The center circle will be open on one side. Whichever sign it opens to is the polarity of the tip. If the circle opens to the plus sign, it is tip positive. If it opens to the minus, sign it is tip negative.

example of "tip positive" polarity schematic

So there you have it. Or I have it…either way it’s there.

Noise Cancelling Audio For Cheap!

December 30, 2009

My big deal headphones headband broke. Both of them. I thought I would have to throw them away and get new headphones. But then I thought about it. I figured in today’s world of DIY videos on the internet, surely there must be a solution.

Then I came across a very nice video explaining that I could fix my headphones and even improve
the sound.

Noise canceling headphones.

This is where I got the idea from:

I went out and bought a pair from Harbor Freights Tools because they were cheaper and because I only needed
the headband. I couldn’t really justify getting the $20 pair off of amazon because I could just go and get
a brand new pair of headphones for $20.

This video shows more how I did it.

So I bought a much cheaper pair and disassembled my old headphones. I found that the plastic grill was too big for my new headphones ear holes and so I pulled the speaker off and just inserted it inside. It fit perfectly with the abundance of
foam inside my new headphones.

My new headphones work great! They do reduce noise and are a great bit. The repair only cost $3.00.

I can live with that.

DIY headphone, earphone wire repair

December 13, 2009

Among the other things I was doing this holiday season,  I got sidetracked with something I’ve been looking into ever since a pair of  good old headphones broke earlier this year.

I love headphones. I have quite a collection, from cheap and crappy to expensive and nice. Well, i bought a pair of earphones from Philips. $15 in Target. I love them. They are clip-ons that fit over the ear, which is good for those whose ears  hurt when using ear buds. These also have a fabric grill and they are all plastic. The ear clips are easily adjustable and they are very convenient. I treasure them.

Well, while in my car recently, I had them in my pocket and the wires were sticking out. They just happen
to catch on my seat belt end on the seat and ripped right off the jack.

ARGH! I really liked those.

Well, what am I to do? I mean, it’s just a wire that broke. I don’t see the point in spending again if everything is fine but the wire broke. So I pulled the rubber jacket off the jack to see where the wire broke off at. It broke up into the jack.
How convenient.

So I attempted to fix these by first stripping off the rubber jacket off the headphone wire. Here, I found three wires.

One ground, and two stereo wires. One was green and one was red. It works like this:
Green = Left Channel, Red = Right Channel, Copper = Ground

I’m used to these wires being insulated with a rubber jacket like that of the outside cord that you can easily
strip off with a razor blade and reveal the copper wire underneath.

This is different.

Now there is an enamel color coating on the wire to keep it insulated as well as keep the diameter of the wire the same inside the overall rubber jacket.I had only seen this configuration in professional wiring and it was done with a type of rubber cement so that you don’t have to use wires or electrical tape. Because that can get messy.

Well, I didn’t know how to get this insulation off and i really wanted to fix these headphones. So, as usual, I went looking around on the internet to see if there was any suggestions. Lo and behold, there were.

The suggestion someone makes here makes sense.

If the wire was coated with an enamel, it then makes sense to simply burn off the insulation and you should end up with bare wire underneath. Then of course, connect the appropriate wires together, like in any regular stereo configuration and you will be good to go.

I did it and it worked. Now I have to solder the  wires together permanently and get shrink tubing to make it all nice, but it worked. And that’s how you reconnect your headphone wire.

If you have lost the jack to the headphones and need to wire another one manually, here is a video showing you what to do: