This DELL 17? Screen (Made in Malaysia under LIKOM model L705XXX, products no: L7055LP) came in and no power symptom. Normally after opening up the cover I would look into the power supply (primary side) for your burnt and cracked features first. If there will be darkened area and used components, I would tell myself that this Monitor needs some more time to repair it. If it is not (component抯 intact) We would usually begin to being let go the filter capacitor and initiate checking the fuse.
Sure, it is confirmed every one the primary side components looks good in such a Monitor.
First, discharge the big fat filter capacitor by having a resistor (I know the fact that voltage already drained off but it's really a normal procedure for me because suppose the start up resistor comes with a open circuit? ) then simply check the fuse.
Generally if the fuse is okay, experience will say that the bridge diodes are also working fine. Place your black probe on your analog meter set to x1 to the center pin (drain) of your power FET and red probe towards other pin one-by-one (gate and source). Generally if the pointer of the meter doesn抰 quit then 80 % of the Power FET is acceptable. If you want to 100% confirm whether it's good then you really need to solder it out and also test. If the pointer displays a reading then doubtless the power FET has changed a short circuit. Your result that I got made by this Monitor was the tip don抰 flick.
Now is the time for me make use of the dick smith flyback tester to be sure the smps primary winding. The result that I got was, the led bar don抰 lit. Ah haya! That was a clue this clue tells you that should be either the smps most important winding is shorted or amongst the secondary diodes has presented with way. Of course you should check all the secondary diodes with the normal multimeter first (remember, every electronic repairers have ones own procedure methods of troubleshooting) but I favor this way as I would like to confirm also if all the smps primary winding is definitely working or not.
Usually smps transformer is amazingly robust thus I didn抰 questionable it to pull along the flyback tester examining. I straight away check lots of the secondary diodes with my own analog meter and uncovered one diode shorted (part phone number U202G). Since I shouldn't have this part number, I use a UF5404 really fast recovery diode as a substitute. In fact I use this UF5404 to all 15 to 17? Monitor as a substitute for all part number of secondary diodes. The spec about this diode was 400volt, 3 Amp through 50 nanosecond.
After the replacement for the diode, and placing the flyback tester probes again with the primary winding, the result shows full bar relating to the LED. Don抰 be pleased about the result yet because your task still hasn抰 done.
Now I progressed to check HOT with the same procedure as checking the facility FET. The HOT checked to remain okay too. Next, I check the inner capacitance of the flyback transformer to see it is shorted or not or would be the capacitance value run. For one's information, internal capacitor in flyback transformer gave a number of problems in computer Watch. I also scanned through the B+ FET and found it to remain good too.
Now is the time to switch for the Monitor, however this round My spouse and i don抰 connect any bulb so it was only a shorted diode in the secondary side. I would only connect a lamp after repair should there be major short circuit from the primary side possibly blown bridge rectifier, shorted fet and smps primary winding along with burnt components in the particular board.
The DELL seventeen-year-old? Monitor worked beautifully and after extended stays of burn-in test, I declared it okay and in a position to send back to my best loyal customer. Isn抰 it fun kid repair a Monitor and afre the wedding you get paid for something that appeals to you doing. I just like electronic repair!
