Shorted Diode Test

The best to test a diode is to remove one lead from the electronic board. Set your analog meter to X 10 k ohms and place it on the diode either way. A good diode should show only one reading but a shorted diode will have two readings. Schottky diodes would have two readings but not shorted reading. So beware as to what types of diodes you are checking. Replace the shorted diode with the spec of same or higher than the original one. Find out the spec form the internet or from your favorite semiconductor data book

How To Check a Blown Fuse

It’s a simple step on how to check a blown fuse. Set your meter (analog or digital) to ohms range or continuity test (beeper test). Place your probes on top of the two edges of the blown fuse. If you got a reading or could hear the beeper sound, this shows that the fuse is okay. If there is no sound or even reading then the fuse is considered faulty and need replacement. Some glass type fuse will tell you how severe is the short circuit in the board.

A dark blown or cracked fuse indicate that that was a heavy short circuit and with only the replacement of fuse will normally cause it to blow again. If the fuse has a slight torn (tungsten) in it chances are high with anew fuse will restore the equipment operation. No matter what it is still the best to put a series lamp bulb to avoid the fuse from being blown again

Checking Capacitor With Ohm Meter

Checking capacitor with ohm meter can be done by using an analog meter. I knew that ESR meter is the best meter to check capacitor (electrolytic) but somehow you also need to use an analog meter to test it. Depends on how big is the microfarad of the capacitor you want to test. Start from X1 ohm and see there is any kick by the pointer (needle) of the meter. If no response then you move up to a higher (more sensitive) scale like the X 1 K ohm. Try moving up the selector until you reach a range where you can see the pointer kick up and then slowly die off. Now reverse the probes and you will see the same thing happen (pointer kick up and slowly settle down).

Be in mind that checking capacitor with ohm meter doesn’t guarantee if the capacitor is okay or not because if a capacitor have loose its capacitance the pointer would still charge and discharge. The best is still you use the digital capacitance meter or even the ESR meter to test if you want to accurately test electrolytic capacitor

How To Test Crystal Frequency

You can test a crystal with a frequency counter or even with an oscilloscope. Some digital multimeter have a built in feature of testing crystal. The range can go as high as 24 MHZ and above. If you do not have the crystal tester you can always build one from a simple crystal tester project circuit at this website. However the frequency range of this crystal tester is not high. If you really have spare time why not building one just to equip your knowledge how the crystal tester work

QUESTION ABOUT FLY BACK TESTER

I test the secondary winding of the chopper transformer which I think its OPEN with the use of flyback tester but only the first light is ON. but when I check with analog tester set to x10k still no reading. I forgot to tell that I remove the chopper from the circuit.


ANSWER

Flyback tester can’t be used to check on secondary winding because it has less turns. How to you know which secondary windings to which-do you have the transformer diagram? If you have then Yes it has an open circuit if no response from your analog meter.

Mosfet TESTER

This is a variation on the astable multivibrator. Circuit was recently developed to test for N-mosfets(the power kind e.g irf830)

I don’t claim circuit can test all bad mosfets or all fault mosfet conditions. If mosfet is working it will operate in the astable multivibrator circuit causing the Led to flash.

A bad mosfet will not cause the LED to flash.

Below is the circuit diagram, the other half of the astable utilizes an npn transistor to make the circuit cheap.

Almost any npn transistor will work in this circuit.

The npn transistor to the right is used as a common emitter buffer that also drives the led as it receives pulses from the mosfet drain
note diode is a light emitting Diode

How To Test a Transistor

CLICK HERE

Test For Yourself

Not Only Electronic Circuit Can Go Haywire, Our Body And Brain Also Could! Don't believe? Try this Test For Yourself!
You will keep trying it to see if you can outsmart your foot - but you cant !

1. While sitting at your electronic repair bench, lift your right foot off the floor and make clockwise circles with it.

2. Now, while doing this, draw the number 6 in the air with your right hand.

Your foot will change direction !

I told you so ! And there is nothing you can do about it !

Welcome to the world of body circuit!

-----------------------

Pass it on to your repair friends. They won't be able to believe it either!

Have a great day!

Method of test capacitors

Measure test paper and ceramic capacitors.

Capacitor paper and ceramic capacitors often damaged in a short or leakage detectors to detect leaks or short freedom we observed the following picture.

Measured convergence test paper or ceramic capacitors .

The image on the ceramic capacitor test measurements, there are three capacitors C1, C2 and C3 have equal capacitance, which capacitor C1 is good, the capacitor C2 and C3 detectors from being short.

When measured from C1 (Capacitor good) to a slightly larger needle and then back to previous position. (Note the convergence is too <1nf>
Measurement test from chemical
Rarely converge chemical detectors or as short paper, but them in a dry or damaged (dry chemical inside the dielectric layer) as the capacitance of the capacitor is reduced, to check convergence and modernization, is often compared degree of convergence with a larger load better convergence with the same capacitance, the image below illustrates the steps to check convergence goods

Measured convergence test chemical
To check the chemical capacitor C2 value is 100μF capacitance can be reduced or not, we still have to use capacitors C1 and the capacitance measurement comparison.
To clock in scale from x1Ω to x100Ω (larger capacitance is to lower the elevator)
Measure and compare the two capacitors of larger loads, then we reverse that sticks several times.
If two capacitors larger load capacitor is equal to better test, we found convergence on larger loads less than the C2 capacitor C2 so on was dry.
Where the needle back up without the capacitor detector.
Note: If the test capacitor directly on the circuit, we need to empty vacuum in a vacuum capacitor from the circuit, then test as above

Leaky Diode

There was a Monitor that came in with no display but with high voltage. The heater was only 2 volt, by right it should be 6.3 vdc. The filter cap checked to be okay with ESR meter and left only the output diode. The output diode was tested with analog meter with the X1 and X10 K ohm range and found it to be good. As usual, if could not find the bad component, the next step was to direct replace the component and retest to see if there is any component that breakdowb when under load. Guess what i found, the output diode broke down when under load.

So, i retest again with my analog meter (set to X1 Ohm) to see if there is any erratic movement in the pointer. At first glance, you thought the output diode was good, but when i applied a little bit pressure on the diode with the help of the probes while still testing the diode, i saw that the pointer have erratic movement. That was the cause of the problem! In future, if you would like to test any diode, i suggest that you apply a little bit of pressure from the test probes and slowly see the result. Don’t test it fast as you may miss a bad diode. Hope this helps!

Testing PWM UC3842 With Analogue Meter

If you are a seasoned electronic repairer, you would have come across many times with this PWM UC3842 IC before. This IC normally use in the SMPS power primary section in Monitor (LCD and CRT Monitors), fax machine, TVs and etc. Sometimes whenever power blows we do not know whether the power IC was affected or not thus we just direct replace the IC and retest the equipment. Generally whenever the power FET shorted this power IC would also gave way. This IC have other equivalent part numbers too like KA3842, IP3842, HA17384 and etc.


Is there a way to test this power IC? I’ve read an article about testing the pin 5, 6 and 7 of this power IC with an analogue multimeter many years back. The article mentioned that one have to treat the three pins like the normal bipolar transistor. If you get a shorted or leaky reading then the IC is bad and if you get a good transistor “like” reading, then the power IC is 99% good. So the question is how accurate is this testing method?

In fact i have personally tested the method and found it to be not that accurate thus i had stopped testing it with analog meter. The reason for it was that i do came across quite a numbers of the power IC test result was good but no power after fixing it. A new replacement restored the power problem. Second reason was that the Monitor display have distortion and after the replacement of the power IC it worked good. Again the Power IC was tested good.

Then, how do i test the UC3842 IC? I just simply replace with a new one and retest the equipment. Do you know that the equipment itself is the best way to test the Power IC and in fact all ICs? If it work i consider the problem solved, and if it doesn’t work, i will concentrate on other parts or area. This IC is not expensive and one should keep at least a few for testing and replacemnet purposes

How To Test Adjustable Precision Shunt Regulator TL431

If you repair the SMPS that have the optoisolator IC connected between the primary and the secondary section, you would usually see a transistor like component. It is actually the TL431 IC adjustable precision shunt regulator and it just like the shape of a C945 transistor. How am i going to test it?

Simple-Set your analog meter to X 10 K ohm range. Black probe to pin1 and red probe to pin 2 and 3 (must have readings) then black probe to pin 2 and red probe to pin 1 and 3 (must have readings). If black probe to pin 3 and red probe to pin 1 and 2-it should have no reading. If there is a reading then it is consider shorted. How acurate is this test? It is 90 over percent and this case is quite similar to my previous post about testing the PWM UC3842 IC. That means, if you still suspicious about the reading then the only way is to direct replace the component and retest the smps again. This component is quite cheap and easily get from those used electronic board especially the SMPS that have the optoisolator in it.

What happen to the power supply if this component is shorted or leaked? It would cause power blink/cycling, low power or even intermittent no power problem

Test Transistor in Circuit

This circuit to Test Transistor in Circuit (PCB), Easy to use. It use IC 4011 or CD4011 or MC14011 or TC4011 , very low cost. Supply volt 9V

Zenier Diode Tester

Zenier Diode Tester

test_transistor

test_transistor

TEST YOUR CRYSTAL

HOW CAN YOU TEST THE CRYSTAL

http://www.4shared.com/account/file/170100741/14238df8/Fun_electronics_Projects_for_t.html



THANK YOU


MOHAMED FATHI

How to Check a Transformer

• voltage test meter
1. Step 1

Multimeter
First you need to get out your test meter, and set it for 120 (240 in some cases, you need to know what supply voltage you have) volts AC. The transformer can be divided into two parts. the supply voltage or high voltage, and the secondary or low voltage. The first thing we need to determine is, are we getting correct supply voltage? The supply voltage wires coming from the transformer can be many colors, the most common for a 120 volt ac transformer supply voltage is black and white. The black being the hot wire and the white being the neutral common wire. First use the black lead of your voltmeter and place the lead inside the wire nut of the black wire of the transformer, place the red lead of the test meter inside the wire nut of the white wire from the transformer. You should read 120 volts ac on your meter. if not then place the red leader to the ground wire, if voltage is now present then you have a bad common wire. If no voltage is present in ether case you have a bad breaker or voltage has become interrupted somewhere along the way and needs to be repaired. If voltage is present then you have supply voltage and now go to step two.
2. Step 2
Now we need to check for the presence of our secondary low voltage. the secondary voltage wires are on the other end of the transformer as the primary you just checked. The colors here can also vary, Most of the time they are red and blue, but may be another color. set your meter to 24 volt AC, and place the red lead of your meter in the wire nut of the red wire, and the black lead into the wire nut of the other color wire, If 24 volts is present your transformer is okay. If 24 volts (or what ever rated voltage your transformer is) is not present replace the transformer. be sure to turn off the power at the breaker before you replace the transformer.
3. Step 3
If wire nuts are not used on your transformer, then you probably have the wires connected by spade connecters. In which case you will check for voltage right at the transformer.
Tips & Warnings
• always be carefully when checking voltage
• if you fell nervous about checking a live load for voltage, you should seek the help of a professional
• be carefully not to touch the leads of the meter together when you are checking voltage