Troubleshooting Power Supply
Troubleshooting power supply can be challenging and once you have master the power supply repairing technique, to troubleshoot other types of circuit such as video, high voltage, horizontal, vertical and etc will take you lesser time. If you understand the functions of how power supply or switch mode power supplies work, you are ready to troubleshoot any type of equipment's power supply as most of them are more or less the same. Once you know the principle you will know the rest. In this article i will not explain how a power supply work as you can read it from your electronic troubleshooting books or you can find one website about power supply from the search engine.
There is many ways to repair a power supply, i will describe one of my way to do it. Whenever a switch mode power supply came in for repair whether monitor switching power supply or computer atx power supply i will make sure to switch on to see what is the problem. Usually the problems are no power, low power, power cut-off after sometimes and power blink. Whatever the problems is i will use a standard procedure to check it.
-check fuse and discharge the big filter capacitor.
-make sure all secondary diodes are ok
-check horizontal output transistor, b+ fet and flyback transformer if you repair monitor.
-scan all electrolytic capacitors with esr meter in the primary and secondary section
-Measure the primary winding of switch mode power transformer with coil tester. Check also the flyback primary winding, b+ coil winding and horizontal yoke coil if you repair monitor. One of these coils short can cause power to blink, power shut down and low power.
-Assuming the problems is in the primary side, i will remove all the components and check one by one. This is the time that really test your electronic troubleshooting skill. It is important to know how to check all the basic components before proceed to voltage testing. If you miss one component, the rest of the checking will be wasting time because you have missed the real culprit. Refer to my past articles on how to test basic electronic components. Primary side usually consist only less than 30 components and it will take you less than 20 minutes to scan thru all the components. Most of the time there will be more than one component found to be defective. Replace the components with exact or near replacement and retest it with a 100 watt light bulb connected across the fuse holder. If the bulb light very bright there is still problem in the power supply. If it goes dim or went off, you know that the shorts had been eliminated and you now can switch on the power supply.