LG W2442PA-BF wont power on.

[Trune]

Hey everyone,

This looks to be a great forum so I thought I would join and learn a little more.

I am trying to fix a LG W2442PA-BF monitor. There is no power at all and originally the fuse was blown. I have replaced the fuse and now it stays intact but still no luck with the monitor.

I have looked around the board the caps look ok.
I have gone around with a multimeter and can only find AC current. I cannot find any DC voltage on the side of the board that says secondary.

Now I don't know detailed electronics but the final place I cam find voltage is what I assume is the input legs of a gh-130 transformer.
Also at the primary side legs of a 817c octo coupler.

I was wondering if anyone could give me some help on what to test and where? Would like to learn

[Trune]

Re: LG W2442PA-BF wont power on.

Second pic

[selldoor]

Re: LG W2442PA-BF wont power on.

Hi - would have preferred straight on pictures of the boards - we need to be able to read the board numbers. When you measure anything you need to tell us what result you got. Anyway first can you test the voltage on the two 68uf 450v caps.
CAREFULLY. as this is high voltage. Put your meter on 600vdc and put black probe on
negative leg and red on positive.

[Trune]

Re: LG W2442PA-BF wont power on.

Okay I will test that and get straight on pics on daylight tomorrow.
Poor lighting is only reason they aren't.

Thanks.

Voltages on the input of the transformer were around 150v but will confirm numbers tomorrow.

[Trune]

Re: LG W2442PA-BF wont power on.

Better pics, hopefully

[Trune]

Re: LG W2442PA-BF wont power on.

Sorry for some reason won't let me put them on one post.

[Trune]

Re: LG W2442PA-BF wont power on.

Ok both caps are 337vdc.

[selldoor]

Re: LG W2442PA-BF wont power on.

Ok Pictures are great voltage on caps is good.

Not sure about the soldering on the fuse,at some point perhaps you can reflow the joints- add some unleaded solder might help.

There is a resistor at R109 is it just a mark on it or is it a hole?

Bottom left corner of the board looking from the top there is a black rectangular component - has T4A on it - this is another fuse. You can test it ( Resistance test first with power off) on the bottom of the board.

As a starter for things to test this is good - start at post19
https://www.badcaps.net/forum/showthread.php?t=10419

[Trune]

Re: LG W2442PA-BF wont power on.

Thanks, I will carry out tests later

Yes, fuse is temporary solution, going to fit a fuse holder if I get it up and running.it looks awful I know

[Trune]

Re: LG W2442PA-BF wont power on.

T4a is fine.

The resistor does appear to have damaged casing. Not a complete hole though.
It's reading 18m ohms one way and -3.5m ohms the other. The reading also climbs as I stay on it.

[Rtech]

Re: LG W2442PA-BF wont power on.

Take it out and measure.

[Trune]

Re: LG W2442PA-BF wont power on.

Of course, sorry that should have been obvious.

138m ohms one way and 130m ohms the other.

I take it that it is destroyed ?

Which type of resistor would this be? Trying to find suitable replacement from maplin.
Bands are green, brown, silver, gold. Is that right, 0.51 ohms?
Can't really find similar on maplin site.

[Rtech]

Re: LG W2442PA-BF wont power on.

Thats is correct 0.51Ω.However with the fuse been blown before,and now the resistor open circuit,you need to be aware that you may have other problems around that area.with diodes or mosfet or the SMPS chip itself.So you need to advise the code on the chip,and if possible find the datasheet on the net.You also need to check the mosfet on the heatsink,this may help if necessary...
http://www.4qdtec.com/mostest.html
or you can measure between its pins and you do not want a short cct .

[Trune]

Re: LG W2442PA-BF wont power on.

Thanks, yeah I guessed there is more to find yet.
I guess it can't be as simple as the resistor giving up?

Btw how do I know what wattage the resistor would be to find a suitable replacement?

I have checked the diodes before and they seem good.

I did try to test the MOSFET Last night with that test, I got a reading of 3.6 but touching with my finger didn't seem to drain, it was late though and difficult with one set of hands.
I am guessing the diode test range they talk about is the beep test, I normally call it a continuity test, is that wrong?

[selldoor]

Re: LG W2442PA-BF wont power on.

I take it that it is destroyed ?

Weird - not seen that before - a grey colour though so is probably a fusible resistor- better get the same type. I would test the diodes first. When you are ready to re test with power you should use a 60w filament 230v lightbulb in the circuit across the fuse, in case you have not bottomed the problem and blow your new parts.


EDIT - Diodes already tested - good

You need to measure the length/width of the resistor to get a clue as the wattage.

Cant just find my link at the moment

[Trune]

Re: LG W2442PA-BF wont power on.

Any pointers on where to purchase them? Does it need to be a 0.51 or can you stray a little (0.47 for example)

Hopefully I start learning fast about these things, finding it very interesting.

Fixed a Samsung plasma for my friend this weekend too, I've got the bug I think!

[selldoor]

Re: LG W2442PA-BF wont power on.

Any pointers on where to purchase them? Does it need to be a 0.51 or can you stray a little (0.47 for example)

I was wondering the exact same thing perhaps Rtech can advise.

Cant find any at Cpc (Farnell) they have 0R47 and 0R56

and there are these on ebay
[url]http://www.ebay.co.uk/itm/4x-0-47-ohm-0R47-0-47R-1W-1-Watt-Metal-Film-Resistor-/200640446205?pt=UK_BOI_Electrical_Components_Supplies_ET&hash=item2eb71a3efd[/url


http://www.ebay.co.uk/itm/2x-0-47-ohm-0R47-0-47R-5W-5-Watt-Resistor-/200640455803?pt=UK_BOI_Electrical_Components_Supplies_ET&hash=item2eb71a647b






Did you get a physical size yet

[Rtech]

Re: LG W2442PA-BF wont power on.

It will probably be 1Watt minimum,and I would probably use 2Watt to be sure.These small values however are usually used in the Drain of the Mosfet,so you really need to take that out and test properly.That would also mean that the SMPS Chip needs to be fully tested as well.If I have a first class stamp,and you PM me your address I can find a tested resistor for you.Also let me have the Mosfet details as I may have one of them as well.

[Trune]

Re: LG W2442PA-BF wont power on.

i would say the resistor is 14mm x 5mm at the end "bulge", circumference 20mm.

Found this at Farnell but no idea if its suitable.
http://uk.farnell.com/international-...w-5/dp/1026689

That would be very kind of you Rtech Maybe that is where i was going wrong, to do the test to drain the mosfet so i need to remove it from the board? I guess i should be using what i call the "continuity" setting on my multimeter?

I will try and get those tested tonight.

The Mosfet is an AUK STK0765.

Let me know if you have any spare, id be happy to pass something your way

[Trune]

Re: LG W2442PA-BF wont power on.

Okay with multimeter set to 200 ohms..
Mostfet STK0765
a) black on pin 1- red on pin 2 - 0.08
b) black on pin 1- red on pin 3 - out of range
c) black on pin 2- red on pin 3 - out of range

But with multimeter set to 2k ohms..
a) black on pin 1- red on pin 2 - 0.000
b) black on pin 1- red on pin 3 - 0.315
c) black on pin 2- red on pin 3 - 0.315

Not sure exactly what that means?