Troubleshooting DELL E173FPB LCD Monitor with power blink symptom is quite easy if you know the right procedure to test it. There are two sections in the monitor that can cause power to blink. It is either primary or secondary section or even sometimes both sections can be faulty. So to isolate as which section is giving problem. I used an automobile 12 volt light bulb (brake light) and connect it between the 12 volt supply line and cold ground with the fuse removed.
If the bulb still blink chances is very high the power primary section have problem.
Do not overlook the other voltages line as well such as the 3.3 and 5 volts. If any components shorted that gets the supply from the 5 and 3.3 volts, the power also may blink.
If the 12 volts bulb lights up we can assume that the power supply is working fine and something shorted further down the line that makes the power supply to blink. If the bulb lights and you continue to check the power section, it will be going to waste your time. You should now concentrate on the secondary section circuit such as the four transistors C5707 that drive the high voltage transformer in the inverter board.
Just think these transistors like horizontal output transistor (HOT) in the CRT monitor that drive the flyback transformer where it worked so hard and chances for it to breakdown is very high. Checking the four transistors off board found one of them have a shorted reading with an ohmmeter.. This transistor can get faulty by itself or it could be some others components that caused it to develop a short circuit such as a defective high voltage transformer but all of the four high voltage transformers checked to be okay with ringer and ohmmeter test.
Now, here is the secret that I’m going to reveal. If you just replace the defective transistor only, chances is very high the transistor or another C5707 transistor will breakdown again. Usually what a technician does is to test the other transistors with either an analog or digital meter. If you use both meters to test the transistors then you have missed out on the faulty transistor because both meters won’t reveal to you the hfe reading of the transistors. Only some digital meters have the hfe checking feature. In other words, you have to use test the hfe reading of a transistor. Although you can replace the other three transistors directly, why not we do some detective work to find the cause of the problem?
Using the Peak electronic atlas component analyzer, I could clearly see the different between a good and a bad transistor. A good C5707 transistor has hfe reading from 320 to about 390 but the bad one reads 467! The other two C5707 transistors have reading about 350. In the above case only two C5707 transistors were replaced and you save the other two. I had burn in test this LCD monitor for many days and it worked perfectly fine.
Conclusion- Whether you repair the DELL E173FPB LCD Monitor or any other model such as the E172FPB or E171FPB, basically the testing method is the same. You could also use this testing procedure on other brand of LCD Monitor too.
Repairing the DELL E153Fpc LCD Monitor with the complaint of display shutdown after few seconds (power LED still on) was not difficult. Normally when this type of problem happens, we would
first suspect the inverter board,
then the filter capacitors and
lastly the main board.
A defective in one of the lamps and a faulty TL1451AC PWM IC or inverter ic may caused the display to shutdown as well.
If the lamp is defective, it will send a feedback to pin 3 or 14 of TL1451AC IC and caused it to stop producing output signal thus the display just shut off once you switch it on. The power board is using a SG6841D pwm ic and a FQPF7N80 power fet . If this power section blow, it is quite easy to troubleshoot because it has fewer components. You can also use other part numbers to substitute the power fet.
As usual, after opening up the cover, I would first check for any burnt components, loose connector, cracked board, dry joints and etc before doing the voltage test. As for the lamps, I would check it last because lamps were seldom spoilt. Upon scanning for any bad components before starting the voltage test, I found a filter capacitor that had turned into darker color. Using the ESR meter revealed the ESR ohm has shoot up to 12 ohms. This filter capacitor located at C922 with the value of 1000 micro farad 16 volt. If you don’t have the ESR meter you can always use the digital capacitance meter. The value that I got from measuring the bad capacitor was 57 microfarad. If you don’t have ESR meter, make sure you get one-it’s fast and accurate.
Now, the question is why a filter capacitor can cause the display to shutdown? If you carefully see the picture, I’ve drawn the yellow path to show you how the voltage is flowing. By the way, the voltage at the bad filter capacitor line is 12 volt. The voltage passed through a SMD transistor in the start circuit and flow straight to pin 9 (VCC) of TL1451AC IC. In order to let the 12 volt to flow through the transistor and reach the vcc pin of the ic, first, a ‘on’ signal must be sent from the main board to trigger the transistor. If no signal send to the transistors (off signal), both transistors can’t be turned on and no voltage will follow through the ic. Thus if the main board or any of the start circuit components spoilt, there will be power but no display because the TL1451AC would not send signal to the Royer type L, C resonant and boost circuit, so no high voltage produced by the high voltage transformer and this will lead to no display.
In the above case, the LCD Monitor display shutdown was due to the ripple because of the bad filter capacitor. The ripple caused the TL1451AC IC to be unstable and eventually shutdown the output signal. Replacing only the filter capacitor solved the DELL E153Fpc LCD Monitor shutdown problem.
Conclusion, don’t always presumed that LCD Monitor is very tough or difficult to repair. From the above article, you could see that the caused of the shutdown problem was only a bad capacitor. If you fully understood how LCD Monitor works, then chances for you to successfully repair the monitor is very high but again it depends on the availability of spare parts. If you ever come across any LCD Monitor sent to you for repair for the first time, go ahead and start troubleshoot it. Who knows one day LCD Monitor repair could become one of the major source of income to you and your business.
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