Transistors Relays In troubleshooting, we use different kinds of basic Electrical and Electronics Engineering Tools but the main and important tool is Multimeter. Now we will check the above mentioned components and devices with this tool one by one. Now connect both terminals, i. So you need to replace it with a new one. Fuse To verify Fuse condition, i.
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If you have any information regarding the illegal reselling or duplication of this bonus report, please report it to jestineyong electronicrepairguide. Many of us when starting in the field of electronic repair check each electronic component one by one by removing it out from the board. This is the right way to test electronic components but it is very time consuming.
For example, if you already confirmed that the power supply section is the main cause of the problem in electronic equipment, you may take about minutes to scan through all the electronic components in the section but for some senior or experienced repair technicians, they can check all of the electronic components in less than 15 minutes and accurate too!
Wow, that was almost half of the time you spent on checking them. This is a big different in terms of efficiency of how many equipment you can repaired in a day. In other word, if you can solve a problem fast, you can actually repair more equipment in a day and more profit to you. Do you know that you can actually check a resistor while it still on board?
This is true especially when the test voltage output from your digital meter is less than 0. If it is more than 0. Another thing you need to know is that if the resistor that you are checking on board parallel with another resistor, you will not get an exact reading.
If you get 0 ohms, this is very obvious that the resistor have open circuit. What if you get 2. This resistor is either open or has gone up in value. Other circuit components cannot possibly increase the value of a resistor; any back circuit could only make the resistance reading lower! Just connect your analogue meter probe to the pins of LED and set your meter to X1 ohm. If there is no light from the LED, just change the polarity of the probes.
You can check LED while it is still in circuit. First you must know what the part numbers of the voltage regulator are, and then you read the specification and locate the input and output voltage and pins. For example, the general type of voltage regulator starts with the part numbers like , , and etc. From the spec you would know that pin one is input, pin 2 is ground and pin 3 is output. If there is input voltage to the voltage regulator and no or low output voltage, suspect the voltage regulator itself faulty or something along the output line that dragged down the output voltage.
Do you know that voltage regulator can breakdown when under full load? Whenever there is any power failure fuse totally blown into dark colour one will always suspect the power FET has gave way. Usually we would use the black probe set to X 1 ohms and place it to the centre pin drain and the red probe to the gate and the source pin.
This is the same way when we want to check horizontal output transistor HOT on board. If there is a reading, chances are high that the FET has developed a short circuit. But you also have to remember that a shorted bridge rectifier may cause the power FET to have reading when check with the analogue meter while it still on board. Checking variable resistor VR on board is not that accurate because of the back circuit besides some VR have their resistance code printed so small at the bottom of the VR.
The best is still removing it out from the circuit and test it with an analogue meter. Any erratic reading can be easily seen from the analogue meter panel compares to using digital meter.
If a coil has less loops small coil , then we can just direct measure it with our normal ohmmeter. A small coil is just like a wire or a jumper and it rarely become defective although it has some inductance value in it. The meter that I use to check the bigger coils is the Dick smith flyback tester. You can check the coils while it is still in the circuit.
Set your analogue meter to X 1 ohm and place the black probe to the centre pin collector of the HOT and the red probe to base and emitter.
It should not register any reading. If there is a reading, most probably the HOT has developed a short circuit. Some HOT in certain Monitor designs are difficult to open you have to remove the whole board in order to unscrew the HOT so to save time follow the example above of checking HOT on board.
You can only test it with a special type of coil meter or the dick smith flyback tester. You can check the primary winding of the SMPT on board without removing it out with the flyback tester. If there are any shorted components in the primary side power FET or in secondary side secondary output diodes the flyback tester will registered a shorted reading and the LED bars would not lit.
Just play around with the flyback tester if you have one and I believe you will quickly notice how it can help you to test a winding fast. Some technicians are using the more expensive type of flyback tester such as the Sencore LC capacitor and inductor analyzer to test the primary winding of SMPT. Just place your meter probes to the switch point assuming the power switch have 2 leads and set your ohm meter or continuity check function.
It should show a very low ohm resistance or the beeper will beep if you use the continuity checker. You can perform this test even if the power switch is still in circuit. You can also use this method to test on the micro switch. Some of the famous optocoupler part numbers are 4N25, 4N35, PC and etc.
Just desolder one pin on each side assuming this optocoupler have 2 pins on each side of the optocoupler. Pin 1 and 2 is the LED light and pin 3 and 4 is the phototransistor collector and emitter. Place your analogue meter probe set to X10 k ohms at pin 1 and 2 either way and it should show only one reading low resistance reading.
This is just the exact same way as when you are checking a normal diode. If it shows 2 reading most probably it had developed a short circuit.
Now place your probes to pin 3 and 4 either way and again it will only show one reading this time the resistance reading is a little bit high. If you got two readings then the internal transistor may have short circuit. If you want to measure an optocoupler that have 6 or even 8 pins, I suggest that you search for its data first from the internet or from semiconductor data book.
Once you know how the internal components are wired, then you will use the best checking method to test them individually. Remember, a shorted optoisolator can cause low power, no power or even power blink in switch mode power supply. Flyback transformer-well I guess most of you all that deals with either TV or Monitor repair has came across flyback transformer in the circuit.
Whenever a flyback transformer have problems it would cause power to cycle, high voltage shut down, no power, low power, arcing, blur, too bright and etc.
Now if you want to check if the flyback transformer is okay or not your first step is to check the internal capacitor with a digital capacitance meter. It should have reading about 1. There would be no reading either way and if you got any readings then this proof that the internal capacitor had developed a short circuit. If the reading is okay then you can proceed to check the primary winding of the flyback. You should check it on board with a Dick smith flyback tester or with any flyback tester that you have.
If you are using the dick smith flyback tester, it should show at least 4 or 5 bars and above. If the tester only shows 1, 2 or zero bars then suspect something has gone wrong with the circuit.
Remember, a shorted diode in the flyback secondary side like the G1 or any other supply lines could pulled down the reading in the dick smith flyback tester. Even if there is only one shorted winding, by using a flyback tester, you can easily find out the faults. Just practice more on this circuit with the flyback tester on different type of 13 monitor so that it would be easy for you to solve problems that are related to flyback transformer. Next is the fuse, you can easily check it on board with your multimeter.
Just set your meter either to ohms or continuity. A good fuse should have reading ohms value and beep sound if you select the continuity test. Replace only with the same ampere and voltage rating of fuse. All Monitors and TV have a Posistor used to degauss demagnetize the picture tube. Normally, the whole degauss circuit consist only the degauss coil, Posistor and a relay for auto degauss. The Posistor may have 2 or even 3 leads. If yes, then most probably something has loosened inside and need to be replaced.
You can even check it on board and if the flyback tester shows 1, 2 or zero bars suspect a defective yoke coil. In order to confirm it, you have to lift up the yoke coils connector and directly measure it.
If it still shows the same result, then most probably the horizontal yoke coil had developed a short circuit between the internal windings. I personally owns an inductance meter and when I compared a known good yoke coil with a bad one, the result was still the same good inductance value but when I compared and checked it with dick smith meter, it clearly distinguish between the good and the bad yoke coil.
You should check it with an ohm meter to determine the ohms value. If you have the expensive Sencore tester, you can always check the vertical yoke coil for any short circuit between the vertical windings. In order to accurately check diodes, you need to desolder one lead and test it with an analog meter set to X 10k ohms range.
A good diode should have only one reading while the bad one will have two readings. Be careful if you want to test a Schottky diodes as Schottky diodes will have two readings but not shorted readings. If you get two similar readings then the Schottky diodes is considered bad. You need semiconductor data book to help you to determine if the diode belongs to which family general purpose, ultra fast recovery, damper, schottky diodes or etc.
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