LG Flatron W2231S no power

[sakoria]

My LG Flatron W2241S is about 4 years old and began shutting down about 6 months ago. In the beginning it would power on after a while but latelly it wont powerup at all. So I opened it up but could not see any visibly defect caps and thought I would take the easy route by changing the smaller caps, 6 of them, but no luck. I've checked the ceramic fuse which measures close to 0.

It still won't power on at all. The new caps are the green ones in the pictures.

I would appreciate any help! I've located it's service manual if it's any help; https://cdn.badcaps-static.com/pdfs/...06480b561d.pdf

I do have soldering experince and I have a digital multimeter but not too much knowledge on how to use it.

[budm]

Re: LG Flatron W2231S no power

You should also repalce start/running caps C103, C105 in the primary side of the circuits.

[selldoor]

Re: LG Flatron W2231S no power

Sakoria - Please can you update your profile with country and mains voltage

[mariushm]

Re: LG Flatron W2231S no power

Check the ends of the lamps and make sure the wires are properly soldered at those ends.

Sometimes a wire is making very poor contact causing electric arches and making the inverter stop for safety.

And while you're there, inspect the lamps, if they're black at the ends or a dark color, they may be simply too old, dying.

[sakoria]

Re: LG Flatron W2231S no power

Check the ends of the lamps and make sure the wires are properly soldered at those ends.

Sometimes a wire is making very poor contact causing electric arches and making the inverter stop for safety.

And while you're there, inspect the lamps, if they're black at the ends or a dark color, they may be simply too old, dying.

Which lamps are you referring to?

[mariushm]

Re: LG Flatron W2231S no power

The monitor has 4 thin fluorescent tubes that look like this:




In the 2nd picture you attached, you have on the left 4 connectors, those are the connectors for the tubes - I may have expressed myself badly because they're not really "lamps", they're fluorescent tubes

There's two tubes at the top, two at the bottom of the screen, usually.

There's silicone "jackets" at the end of the light bulbs which you can GENTLY pull away to see the actual place where the wire is soldered to the tube :



Sometimes the wires inside the jacket is loose and isn't soldered anymore to the light bulb, or is just burnt out (weak solder made connection not so perfect and since there's 700v going through the wire, it can burn out from sparks)

Also, if the tube is brown/dark yellow or black at the ends, it just means it's very old and maybe it's pulling too much current from the inverter (tubes going bad do that or fail to start triggering the inverter protection) so you'd have to replace them.

People that fix monitors often make their own test lamps by stripping out the electronics from normal fluorescent lightbulbs you see in store and attaching a connector like the one inside your monitor directly to the fluorescent tube in the light bulb.
Then, by replacing one connector with your test bulb that you know works, you could tell if the fluorescent tube is faulty.

budm here on this forum has a picture gallery where he shows faulty light tubes and wires : http://s807.photobucket.com/user/bud...%20lamp?page=1 hope it shows what i mean

and he's his replacement lamp made from an old cfl lamp : http://s807.photobucket.com/user/bud...d%20CFL?page=1

[sakoria]

Re: LG Flatron W2231S no power

Is this also applicable when the monitor does not power on at all?

[mariushm]

Re: LG Flatron W2231S no power

No, the monitor should at least have its standby led blink for a bit, or when you push the power on button there should be some light for a few seconds.

You say you have voltage on the primary capacitor, so the fuse isn't popped.

You have to check if there are voltages at the output of the power supply, which is that connector on the power supply under the green capacitors. You should have there 12v, 5v and possibly other voltages. Some of those pins in that connector are for the inverter to power on and off and to adjust brightness

You have the manual, follow the flowcharts starting from page 14.. follow the troubleshooting steps. Measure what it asks, and see where you get stuck.

For example when it says Check J703 voltage pin 5, 6 ... go down to page 22 at the display board schematics and see which one is the connector J703, or look straight at the display board, it should have J703 written there (hint, it should be the cable coming from the power supply plugged in it)


On page 22 you have the design of the display board and there you have the connectors described, what each pin/wire in that connector is supposed to receive from the power supply.
On page 23 you have the design of the power supply

[budm]

Re: LG Flatron W2231S no power

"caps C103, C105" Did you check or repalce them? You can also try heatimg them up with hair dryer to see if the power supply will start up.

[sakoria]

Re: LG Flatron W2231S no power

I noticed that the PSU PCB was mounted with 4 screws and 2 of these had metal plating which led me to believe that these completed the circuit or grounding and as soon as I mounted them the monitor started working! Will be running it 24/7 to see if the cap replacement was enough! Thanks guys!

[budm]

Re: LG Flatron W2231S no power

The power supply will run by itself without mounting to the chassis, it is an always on power supply. The main board may use the metal chassis for the ground connection to the power supply ground, then you should also tighten the main board mounting screws also. I always see at least one ground wire between the main board and the power supply board, otherwise it would have been hard to do pre-test of the boards out off the chassis.