Sometimes I Do Make Mistake In Repair
Customer sent in a 15″ LG LCD Monitor with the complaint of no power. I found the fuse already open circuited and on board check found the power FET have shorted reading in all the 3 pins. Since I’m not familiar with this model I have to check all the components in the power side. I found the big filter cap had no reading and the rest of the components were good including the SMD components. Since the power FET already shorted this means the power IC will also be affected and need to be replaced. So total all I replaced a fuse, power fet, power ic and the big filter capacitor (68uf 450 volt).
In this repair I’ve actually missed out the 5.1 volt zener diode (ZD4) and because of this mistake the power would not start when powering it up. When i rechecked the power section later did I found that I was actually missed out on this particular component. A replacement brought the power back to life again.
Lesson learnt here is that when you want to check the whole components in the power section ,make sure you check them all and also make sure you know how to check it. If you do not know how to check those components you can refer to my ebook on Testing Electronic Components.
For your information some of the SMD components can be checked on board especially the resistors because the value registered at the meter is almost the same as the printed value. This means if the SMD resistor is marked as 103 (10 K OHM) and your meter got about 9.95 KOhm then you don’t need to remove the resistor and test it off board.