Welcome to DuMall.com

WARNING:
When testing any form of electronic equipment
there are several precautions you must take.

First, make sure the equipment is disconnected from
any form of power supply, this includes but not
limited to power sockets from walls and Batteries.

Second, be aware that devices such as Televisions, microwaves
and so forth, contain components which can hold enough electrical
current to stop as human heart, "Even Hours" after it has been
removed from a power supply. So if you don't know what it
is, don't touch it and if you do, take extra precautions when working
with such devices; even the experienced can die with a simple mistake.

Third, electrical current can damage your testing equipment
when used improperly. So always make sure that your
testing equipment is set to the correct testing mode, voltage
and Amp settings. Most important make sure that your
testing equipment is the correct equipment for the job.

****Please read all of the instructions for each test before attempting it.****
****Any WARNINGS or recommendations may be missed if you do not do so.****

Equipment Required for tests: Digital Multi-meter or DMM- A multi-meter is one of the most useful devices you can get your hands on when working with electronics. Whether you are repairing or simply tinkering around building projects. Best of all you can get an inexpensive $10.00 (US$) multi-meter almost anywhere these days. Depending on your needs or desires, you can spend a lot more money, the more you spend the more features you are likely to get. But please remember, just because it is expensive it does not make it the best. You might find that when building simple projects a ten dollar multi-meter will do. The most important features you need in a multi-meter are the following: Voltage testing, both DC and AC, Resistor testing, and Diode testing. If it has extra features then all the better.

Capacitor Testing

If you don't have the correct equipment for testing a capacitor here is a simple way to do it. Most capacitors will rarely become damaged, and when they do you might find the following physical features; arcing or burning at the insulator, the presence of what looks like an oily film on top of the capacitor or under it. A oily kind of smell is also a good sign that it may be defective. The last possible physical indication is the most easy to spot, any bulging on the capacitor means that it either has broken down or is in the process, which means that it needs to be replaced.

If none of the signs mentioned above are present, but you still suspect that a specific capacitor is causing the problem, you can test it in the following manner with your trusty multi-meter, this test is good for capacitors for about 200v, it is not recommend that you try this test with any capacitor above 200v, it has not been tested at a higher setting.
(Note: This test is not meant for high power capacitors, such as in a microwave. If you are testing a microwave capacitor please go a little further down. Do not use a multi-meter on a capacitor that exceeds the multi-meter's maximum voltage rating in the following manner; it may damage your multi-meter and/or cause personal damage.)

Voltage Test

1. Put your multi-meter a couple of volts above the voltage setting for your capacitor, 5-10 volts above should do.

2. Take the positive probe (usually red) and place it on the positive end of the capacitor or the led on the side without the negative strip.

3. Place the negative probe (usually black) and place it on the negative end of the capacitor or the led on the with the negative strip.

4. Now look at you multi-meter, you should get a voltage rating. It may not be the exact voltage rating of your capacitor, especially if the device has been turned off for a while. It should slowly begin to go down as the multi-meter uses up the power stored within it, if you get a reading it should be good.

(No voltage reading, read below)

Ok, I tried it and I didn't get a voltage reading.

This may happen for one of two reasons, the capacitor is broken or it is discharged. Lets assume that it is discharged rather than broken because the test is not over. If you have a multi-meter with a diode test setting this test will be a lot easier.

1. Set you multi-meter on diode test mode.

2. Take the positive probe (usually red) and place it on the positive end of the capacitor or the led on the side without the negative strip.

3. Place the negative probe (usually black) and place it on the negative end of the capacitor or the led on the with the negative strip.

4. Step 2 and 3 will slightly charge the capacitor, not to a very large voltage just a couple of volts depending on your multi-meter.

5. Remove the test probe's from the capacitor after about 30 seconds and repeat the first voltage test from above.

(Still No Voltage Reading)

The last way you can test your capacitor and it is usually done as a last resort is to remove it from the device and follow the previous steps. The reason for this is that in rare occasions other components may be draining the power when you charge it and since you will have to remove it to replace it, you should test it when you take it out. But please be absolutely sure that the problem is the capacitor and not another component. It can become tiresome removing capacitors only to find out that they are in working condition and then to find out that it had nothing to do with the capacitor. So unless you are absolutely sure that it is the capacitor, don't remove it until you have tested any other possible components. As I previously stated, capacitors will rarely breakdown and if they do, it may be an indication that something else may have broken down.


Testing High voltage capacitors § Top of Page § Warning: Never work on any device while it is still plugged in, check and double check to make sure it is unplugged. Second, never do any live tests or test an electrical device while it is in operation. Please leave this practice to the brave professionals who have been doing it for a long time. The following test is of course if you don't have the proper equipment to test a capacitor. The first thing we need to do to test a high voltage capacitor, such as a capacitor from a microwave is the following:
	1. First, verify that the device is unplugged. 2. You must first discharge the capacitor, this is done by doing the following: Touch the blade of an insulated-handled screw driver to one terminal and then sliding it toward the other terminal until it makes contact, when it does hold it there for a few seconds. (This can cause a rather loud and scary "pop!", but if there is a spark, the capacitor is most likely holding a charge, therefore it is most likely not defective.) 3. Do step number 2 for each terminal on the capacitor if it has more than two and from each terminal to the chassis ground. If the device has more than one high voltage capacitor repeat step 2. 4. Next we need to isolate the capacitor from any other components. Do this by removing all the terminal connections attached to it. But remember where all the connections go, if there is a resistor attached to it do not remove it. 5. Set your multi-meter to test for resistance(ohms); put the level to it's highest. Now measure from one terminal to the other, you should get an infinity rating. Then remove the probes and put them in the reverse position. It should measure about zero and then slowly move back to infinity. Do this for every terminal on the capacitor. (Note: If there is a resistor attached to it you may get the rating of the resistor instead of infinity.) 6. Last, measure from each terminal to the metal casing of the capacitor it should read infinity. 7. One last note, if the capacitor has an internal diode it will read the diodes forward resistance or the resistance of power that it allows to flow through it.
If you have performed the above test and it went as described, then the capacitor is most likely in working condition. This is a crude test, but mostly effective.

Diode Testing § Top of Page §
As with a most electronic components, physical damage is the first sign to look for in a diode. Some good signs of a damaged diode are: a burned cracked diode, a spot that looks like a blister (it kind of looks like a small cigarette burn sometimes), some diodes will even be split in two, you can also look for a burnt smell coming from the diode, this is a nasty smell, you can't miss it. If there are not physical signs the you will have to test it. If your multi-meter has diode testing mode then this will be very easy.
	1. Make sure that the device to be tested has been removed from any power source, this includes but not limited to wall sockets, batteries, etc. Discharge any high power capacitors in the manner described in the section for testing high power capacitors. Then simply put the multi-meter on diode testing mode and then do the following. 2. Take the positive probe of your multi-meter and place it on the end without the stripe next to it, this is the negative end. 3. Take the negative probe and place in on the end of the diode with the stripe, this is the positive end. Now you must be wandering what in the world is going on, I'm putting the probes on positive ends. Well there is a good reason for this; the positive end is sending and electrical signal through the diode and the negative end is receiving it. You should get a reading on you multi-meter, which will depend on the size of your diode. 4. Take the probes and put them in the reverse position from step 2. Now you should get an infinity reading. If you do and you got a reading in step 2 then the diode should be in working condition. If you get a infinity reading for both, then the diode is most likely damaged. (My multi-meter doesn't have a diode testing mode. Read below)
My multi-meter doesn't have a diode testing mode. Don't worry if your multi-meter doesn't have a diode testing mode, all is not lost. The following is a simple test you can do with the resistance (ohms) setting of you multi-meter. Though it may not be as accurate as with that of an actual diode test. The reason for this is that you may get false reading due to resistors near the the diode. But if you get false readings as describe below, you can fix this by removing one end of the diode from the circuit or circuit board. This can be easy sometimes to do, but inconvenient at other times. But without the correct equipment it may be necessary. Now to test the diode do the following:
	1. Put the multi-meter on resistance (ohms) testing mode. 2. Take the positive probe of your multi-meter and place it on the end without the stripe next to it, this is the negative end. 3. Take the negative probe and place in on the end of the diode with the stripe, this is the positive end. Now you must again be wandering what in the world is going on, I'm putting the probes on positive ends, again. Well there is a good reason for this; the positive end is sending and electrical signal through the diode and the negative end is receiving it. You should get a reading on you multi-meter, which will depend on the size of your diode. This reading doesn't really matter, it just matters that you are getting it. 4. Take the probes and put them in the reverse position from step 2. Now you should get an infinity reading. If you do and you got a reading in step 2 then the diode should be in working condition. If you get a infinity reading for both or you got a reading from both ends then you will have to remove one end from the circuit or the circuit board in order to verify the results. 5. After you remove one end, repeat steps 2-4. If you still get a reading of infinity on both ends or a reading on both ends, then the diode is probably broken. Since you will have to remove the diode to replace it, test it again once it is removed, just to be 100% sure. As I said at the beginning of this test, it is not the most accurate.
§ Top of Page §