Partisan Repair – Part One: Resistors and Capacitors, by DN

So you want to fix electronics huh? Luckily for you it is easier then you think; personally I have trained many people who have had no experience with electronics or soldering for that matter, typically withing a few weeks they can stand on there own two feet. They will still have a million questions but they possess the necessary basics to find the answers and best of all they are getting stuff working. The goal here is to make this as straight forward as possible, I am intentionally skipping over a lot of things I don’t think matter right now; so all you super nerds please don’t hate me for not covering many technical details.

Let’s get to it.

As someone new to electronics schematics can make things a lot more confusing. They are great when you have them but chances are you won’t have any, so what do you do? You check everything; every component in the device if possible! You don’t need to know how the circuit works or even what the thing does. If you check every basic component you will find the problem most of the time. Check the stuff that is easy to check with a multi-meter first. Also note please don’t check electronic components with the device powered (that time will come later). In fact make sure you also unplug it!

Resistors

Typically a failing or broken resistor will start to look like a open circuit, or in other words it’s resistance starts to rise or become infinite. Resistors take much time to get down and memorize.

Before you go checking your resistors you need this!

Photo taken from http://mfranzen.ca/images/pics/classes/comp/bb-resistor-colour-chart-l.jpg

If this chart makes no sense to you look at it more and you will figure it out. The number of bands on the resistor will determine how we read the resistors color code. So the four band from the chart we see (brown= first digit=1) (Black=second digit= 0) (Orange=Multiplier=1,000) (Yellow=Tolerance=5%)……So the easiest way for the multiplier is just drop the 1 at the beginning. So you got a 10K Ohm resistor with a 5% tolerance.

Look found some resistors! Lets check them!

On this meter OL means it does not measure anything. So we have a open resistor. Also remember set the meter to resistor mode! The Ohms symbol!

Although in the photo you cannot see the colors to determine its resistance we will pretend it is a 5% 100 ohm resistor. So this resistor would be good if it were to measure anywhere between 95-100 ohms. Also since we need to replace this resistor we need to know it’s wattage rating. Based on the dimensions of the resistor is how you determine it’s “wattage”.

A chart can be found here:

Look at this juicy one. He should be a 1.2K Ohm 5%

This one reads low? So what we need to do remove it from from its circuit.

So to break the circuit pull up one leg on the resistor.

Now with the circuit broken he looks good! Problem is the circuit has resistance and resistors in parallel measure lower in circuit.

Well some nice person printed its value right on this one! So it’s 0.68 ohms!

Ummm? My meter measures it at 1.2 Ohms. Maybe that resistor is bad?

When resistances get small and you are using a multi-meter a thing called meter loading needs to be taken into consideration. So you can see the resistance of my meters leads etc has about 0.4 ohms of resistance. With a little math 1.2-0.4=0.8

We could conclude that the resistor is most likely fine. For resistors with low resistance a good tool to have is a LCR meter. But a handy thing on many meters is its relative setting. Put the leads together and push the relative button and it subtracts that reading and now uses it as a new reference point.

Now when we read that resistor in relative mode she looks good for sure.

Capacitor

You can look up on the internet what a capacitor does – I will not go over that much here. 99.999% of the time you find a bad capacitor it will be a electrolytic capacitor. Capacitors in circuit can be a pain to check. But chances are if the piece of equipment is like 30+ years old just replace them especially if it is power electronics like inverters, switching power supplies and VFDs. If the caps smell like fish you know they are bad.  Capacitors are either polarized or Bi-polar (non-polarized, un-polarized whatever)! We will only go over aluminum electrolytic capacitors for now. But if new to this once again check everything if you can.

So the information you may find on a capacitor is it’s voltage rating (it could be either AC or DC rating) capacitance and sometime it’s tolerance you may also need the manufacture and series of the capacitor because some are special. We know this is a polarized capacitor because of the white line you see on it. The white line is the cathode or the (-). The other leg is the anode or the (+). Put these in backwards and bad things happen. Oh ya set meter to capacitor mode.

So this is a 100uf (micro farad) capacitor. Assuming its tolerance is 10% I will accept anything between 90-110uf. So from the picture we can see that this capacitor is bad.

Capacitor is blurry in the photo; however my meter does not read anything from this capacitor, so it is bad!

Well this capacitor looks good. You can put it back in circuit if you like or if it is old and you can get the part I say spend the $0.40 cents and replace it. Also remember to try and find out what product line or series it belongs to so you can know to buy a high frequency, low impedance, high temperature capacitor etc.