Library Science, Owner's Manual Repair Guide

Likom L705xxx Model, Dell Monitor Repair With No Power Symptom

This DELL 17" Monitor (Made in Malaysia under LIKOM model L705XXX, product no: L7055LP) came in with no energy symptom. Normally after opening up the cover I might have a look at the power provide (primary facet) for any burnt and cracked components first. If there are darkened space and burnt elements, I might tell myself that this Monitor wants a little extra time to repair it. If it's not (component's intact) I'd normally begin to discharge the filter capacitor and begin checking the fuse.

Okay, it is confirmed that all the first side parts appears to be like good on this Monitor.

First, discharge the large fat filter capacitor with a resistor (I do know that the voltage already drained off but it is a normal process for me as a result of what if the start up resistor has an open circuit?) then test the fuse.

If the fuse is okay, expertise will inform you that the bridge diodes are also working fine. Place your black probe of your analog meter set to x1 to the middle pin (drain) of the power FET and crimson probe to the other pin one after the other (gate and source). If the pointer of the meter would not kick then eighty % of the Power FET is okay. If you want to one hundred% confirm whether it is good then you need to solder it out and test. If the pointer shows a studying then most likely the ability FET has developed a short circuit. The result that I got from this Monitor was the pointer don't flick.

Now's the time for me to make use of the dick smith flyback tester to check the smps primary winding. The consequence that I bought was, the led bar do not lit. Ah ha! That was a clue and this clue tells you that it's either the smps major winding is shorted or one of the secondary diodes has given way. Of course you can examine all the secondary diodes with your normal multimeter first (keep in mind, every electronic repairers have their own process strategies of troubleshooting) but I favor this fashion as I wish to verify additionally if the smps primary winding is working or not.

Often smps transformer could be very sturdy thus I did not suspect it to drag down the flyback tester reading. I straight away check all of the secondary diodes with my analog meter and located one diode shorted (half number U202G). Since I would not have this half quantity, I use a UF5404 extremely fast restoration diode as a replacement. In truth I use this UF5404 to all 14 to 17" Monitor as a alternative for all half variety of secondary diodes. The spec of this diode was 400volt, 3 Amp with 50 nanosecond.

After the substitute of the diode, and putting the flyback tester probes once more to the primary winding, the consequence shows full bar on the LED. Don't be pleased with the outcome yet because your job nonetheless hasn't done.

Now I moved on to check HOT with the same procedure as checking the ability FET. The HOT checked to be okay too. Next, I verify the inner capacitance of the flyback transformer to see it is shorted or not or is the capacitance worth run. In your data, internal capacitor in flyback transformer gave lots of issues in laptop Monitor. I additionally scanned by the B+ FET and located it to be good too.

Now could be the time to change on the Monitor, nonetheless this spherical I do not connect any bulb as a result of it was only a shorted diode within the secondary side. I might solely connect a light bulb after restore when there's main quick circuit within the primary facet similar to a blown bridge rectifier, shorted fet and smps major winding and likewise burnt elements in the board.

The DELL 17" Monitor worked superbly and after lengthy hours of burn-in test, I declared it okay and ready to send back to my loyal customer. Is not it enjoyable to be able to restore a Monitor and on the end you get paid for something you like doing. I simply love digital repair!

Likom L705xxx Model, Dell Monitor Repair With No Power Symptom

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