Dell E151fpb LCD monitor came in alongside the complaint of no power but upon carefully check out the LCD you could see a very light (blur) white flashes across the screen and the power LED is not lit. Removing the cover was a bit easy compared to other models. As usual whenever the mainboard and power board were exposed, I would personally look for any bulged capacitor, darkened area, a loosen connector and etc. However this monitor boards looks perfectly fine. The next step was to separate the power/inverter board a problem main board. Power was applied for the power board there isn't anything could hear a soft 'chip-chip' sound. As i measure the 12 volts line by using a digital multimeter, the readout was about 7- 8 volts which was very unusual. In fact this is wonderful to us because we know what the next step that anyone should make.
Now we may also use a 12 volt automobile brake light to test wherever section that is bringing about the low voltage output problem. In case the LCD monitor designed to run on 18 or 24 volts then you may make use of a light bulb from the big trailer. A defective component in either primary or secondary side could cause low output current. Removing the fuse as shown in the photo and connect the bulb in regards to the supply line along with the cold ground could tell which section is giving hassle. You could use this method but initially you can must confirm that the secondary filter capacitors, TL431 adjustable precision shunt regulator ic, optoisolators and components surrounding the optoisolator is working a person proceed to make use of the light bulb.
When the power is on the light bulb still do not lit and the sound still could be heard. This signifies that the primary side is having problem and we can leave the inverter/high voltage area and fully concentrate find the faults however section.
This is time to really test out your basic electronics skill because you now know at the area in which the fault is and you just need to use your skills to locate the precise bad component. Have been not much components in the primary side, and consume a lot of easily check every one of them in lower 20 minutes. After checking all the constituents I was surprised that all of them tested okay. Primary winding of switch mode power transformer rings 8 bars which indicates good and even the uc3842b PWM power IC replaced the power still won't projects! It was quite challenging to troubleshoot this type of problem where a person hundred percent without the primary side is giving problem yet you are unable to find out at fault.
Since Experienced checked all the components and may not locate the fault, the best way that I could do would direct replace the semiconductor devices such as the diodes, scr, fet, and transistors. From experienced I do encountered semiconductor components breakdown when under full operating voltage. Separately of the semiconductor components I replaced and turn on each time I had changed it to decide if the bulb light up or not. Guess what, you would believe what have I simply discovered-a defective 2N7000 fet! The moments I have replaced this fet and power on, the bulb immediately smoke. I could not believe diet plans . this faulty fet that causes all the output voltages to drop! I was so happy that I eventually reduced the problem and who knows this may be a common fault for all DELL E151Fpb LCD monitor- so please take note to all LCD monitor repairer.
I started to check again the defective 2N7000 fet with my analog meter and peak electronic atlas component analyzer and outcome is still the same-tested good! Exactly like flyback transformer, the best testing equipment to test Fet as well components is in fact the equipment itself although it runs on full operating voltage, frequency, signal and etc. An individual have just learned at this point was whenever all the suspected components tested good, the finest to reveal the reality is to direct replace the various components. Hope you love this particular article even better good articles to come everyday! Wishing you all of the best and happy repairing!
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