LG1915S backlight problem

[mr.tight]

HI people!

Never done this before, but have soldering iron and solder, (with some electrical experience too)

After 3-4 years, my monitor is playing up. For the last few weeks, ive come home to switch it on, and only get a quick flash with green light remaining on. (yes, i can see image with a torch). It took 1-2 hours of leaving it on and the monitor would usually work after a few presses. Last two days, and it refuses to play ball. Time to buy new or repair. Things are rather tight for me right now, and i dont think ive had my value out this monitor yet either. Doing some searching, im learning about capacitors being a common problem in these machines (pre- 2007?).

I have removed the power-supply board and inspected the capacitors, but im not seeing any significant bulging or leakages (after i realised those white blobs were just glue!) They are Samxon, and i think '(M) GF (M)' might mean something to you? Anyway, the shorter capacitor looks totally flat, but the 5 larger ones seem slightly distorted but its hard to tell. I hope to attach some pics of the board now, and hope you will see if they are good or not. I have a maplins local to me (in the UK) and i'll call them tomorrow to see if they sell these caps. £140 is too much for a new monitor, so if this is cap problem, im fixing it myself!

On viewing the side of the caps, they dont protude the top.

Please help, many thanks indeed!
Nick

[retiredcaps]

Re: LG1915S backlight problem

Last two days, and it refuses to play ball.

1) Currently, if you power it on, does the LED light up?

2) If the light is on, can you see the image using a torch or flashlight?

3) Can we get 5 shots like the following (so we can see the entire board)? See

https://www.badcaps.net/forum/showpo...94&postcount=1

4) Do you have a multimeter and can you measure voltage?

[mr.tight]

Re: LG1915S backlight problem

1) Currently, if you power it on, does the LED light up?

2) If the light is on, can you see the image using a torch or flashlight?

3) Can we get 5 shots like the following (so we can see the entire board)? See

https://www.badcaps.net/forum/showpo...94&postcount=1

4) Do you have a multimeter and can you measure voltage?

Thanks for the reply.

1. yes it does
2. yes i can. (as mentioned)
3. The other board is fixed to the back cover, which i think is the inverter board? I can post a pic of that (birds-eye view) and another of the main board in better light. I'll do that now.
4. i do, but not that great with them, will need new batteries too)

Its just not that obvious to me which caps are bad, so perhaps i could replace those large 5 ones, as the shorter one looks perfect. Ofcourse, there are lots more components that could be bad, im just hoping this could be simple.
thanks again.

[retiredcaps]

Re: LG1915S backlight problem

2. yes i can. (as mentioned)

It wasn't clear whether the torch trick works currently or 2 weeks ago.

3. The other board is fixed to the back cover, which i think is the inverter board? I can post a pic of that (birds-eye view) and another of the main board in better light. I'll do that now.

Yes, we will need a picture of the "panel" board. We also need a picture of the backside of the power and logic board.

Its just not that obvious to me which caps are bad, so perhaps i could replace those large 5 ones, as the shorter one looks perfect. Ofcourse, there are lots more components that could be bad, im just hoping this could be simple.

If the power LED is on and can see the display using a flashlight/torch, it is unlikely that the 5 caps you looking at are bad.

[retiredcaps]

Re: LG1915S backlight problem

Sorry, one other important question.

Does the LCD display briefly display the image at the beginning (like less than 2 seconds)?

Or is it black to begin with?

Depending on your answer, it will obviously affect how we troubleshoot this.

[mr.tight]

Re: LG1915S backlight problem

Thats a shame. I will have to take the panel board off, so i will do that tomorrow, and will take pics along with the backside of the power board too. If it means i will have to test each component and spend hours of experimenting, then maybe i will just fork out for a new monitor. Thanks for your help.

Nick

edit: It flashes up for a fraction of a second everytime i switch from off to on, or the display refreshes from the graphics card. I waited many hours yesterday expecting for it to eventually work, but it never did.

[retiredcaps]

Re: LG1915S backlight problem

I will have to take the panel board off, so i will do that tomorrow, and will take pics along with the backside of the power board too.

For the panel, we don't need a picture of the backside, just the front side. In fact, leave it for now because your answers to the following questions below will have dictate whether we need a picture or not.

If it means i will have to test each component and spend hours of experimenting, then maybe i will just fork out for a new monitor.

I don't know why you are already admitting defeat when we haven't even started yet?

Right now, you are totally focused on those 5 capacitors. The symptoms suggest otherwise.

At this point, I'm gathering as much information as possible so that members here can make informed suggestions on what to test. The more info we get, the more we can narrow it down to a certain area.

If you are not willing or do not have the patience, then maybe it is best for you to buy a new monitor and sell your old one?

edit: It flashes up for a fraction of a second everytime i switch from off to on, or the display refreshes from the graphics card.

Just to clarify, you can see the display briefly each time you power on/off?

[mr.tight]

Re: LG1915S backlight problem

For the panel, we don't need a picture of the backside, just the front side. In fact, leave it for now because your answers to the following questions below will have dictate whether we need a picture or not.



I don't know why you are already admitting defeat when we haven't even started yet?

Right now, you are totally focused on those 5 capacitors. The symptoms suggest otherwise.

At this point, I'm gathering as much information as possible so that members here can make informed suggestions on what to test. The more info we get, the more we can narrow it down to a certain area.

If you are not willing or do not have the patience, then maybe it is best for you to buy a new monitor and sell your old one?




Just to clarify, you can see the display briefly each time you power on/off?

hi, Heres the underneath of the power board (the panel board pic i attached earlier)

The backlight comes on, but its only a flash on the screen, youd be hard-pushed to find your mouse arrow! I get the flash when i power on, or 2 or 3 when the pc boots up and goes though start-up. Sorry if im not being clear.

I appreciate your help, no doubt about that. What would you suggest my next action?

thanks

[mr.tight]

Re: LG1915S backlight problem

also, i was focussed on those capacitors because i found a thread where the symptoms matched, and it was fixed by replaciong those caps. Perhaps i might be confusing this as the same problem. http://www.fixya.com/support/t368291...shes_instantly

[retiredcaps]

Re: LG1915S backlight problem

What would you suggest my next action?

What are the part numbers of U303 and U304 on the backside?

[retiredcaps]

Re: LG1915S backlight problem

also, i was focussed on those capacitors because i found a thread where the symptoms matched, and it was fixed by replaciong those caps. Perhaps i might be confusing this as the same problem. http://www.fixya.com/support/t368291...shes_instantly

I understand what you are saying and in the end it might very well be the caps are bad, but I'm trying to gather as much information as possible because several members here will ask for the same.

It could be just bad caps. Or bad caps and a shorted transistor. Or bad caps with a bad ccfl. Etc.

[mr.tight]

Re: LG1915S backlight problem

What are the part numbers of U303 and U304 on the backside?

That was unbelievably hard to read! omg! therefore, even with magnifying glass, i may still have a digit wrong, but this was what i could make out:
Nikos, P2103NVGG4549841

[mr.tight]

Re: LG1915S backlight problem

I understand what you are saying and in the end it might very well be the caps are bad, but I'm trying to gather as much information as possible because several members here will ask for the same.

It could be just bad caps. Or bad caps and a shorted transistor. Or bad caps with a bad ccfl. Etc.

I'll see if i can buy those caps easily, and if i can, then it wont hurt to replace them and fingers crossed. I did read from wikapedia that mass cap production for use in lcd monitors, were sub-standard between 2000 and 20007. You know more than me, clearly, so im not going to give my opnions any credit.

[retiredcaps]

Re: LG1915S backlight problem

I'll see if i can buy those caps easily, and if i can, then it wont hurt to replace them and fingers crossed.

Caps don't have to be bloated in order to be bad. They can be out of tolerance uF wise and/or have high ESR (ohm).

Having said that, all I'm trying to do is help make an informed decision rather than "shot gunning" and guessing.

Right now, I'm the only one who is asking questions, researching, and digesting this information. Others may join in and add their insight.

If you want to rush and buy the caps, go ahead. If this were my monitor, I would at least want to do some basic troubleshooting and have some evidence that it is the caps. We haven't even done one single test yet!

[retiredcaps]

Re: LG1915S backlight problem

P2103NVGG4549841

How is actually written on the chip? Like this?

P2103
NVGG
4549841

It matters because it will help find the datasheet.

[mr.tight]

Re: LG1915S backlight problem

Caps don't have to be bloated in order to be bad. They can be out of tolerance uF wise and/or have high ESR (ohm).

Having said that, all I'm trying to do is help make an informed decision rather than "shot gunning" and guessing.

Right now, I'm the only one who is asking questions, researching, and digesting this information. Others may join in and add their insight.

If you want to rush and buy the caps, go ahead. If this were my monitor, I would at least want to do some basic troubleshooting and have some evidence that it is the caps.

I hope i can find that evidence shortly then. If im none-the-wiser by saturday, and if i can get them, ill buy that set of caps, after-all, its all i hear about "bad caps!" Im not the specialist, you are, but i'll admit, i just want my monitor back...

thanks for your time, and im up for testing, if youre up for it too.

[PlainBill]

Re: LG1915S backlight problem

I think you may have two problems here. The slow startup is usually an indication of failing capacitors. The brief flash of light is usually caused by a problem with one of the CCFLs. 'Two seconds to black' can be caused by bad capacitors. It depends on the design of the inverter; sometimes they have a very short startup time. Samxon's are not known for high quality, but I am not aware if they are known to fail without physical signs.

I see two approaches. The first would be to replace every electrolytic cap on the power supply / inverter except the large 450 volt one. I count 9 caps, including the two small ones by the transformer. If you are in the USA this will cost about $10 - $12 from Digikey if you specify USPS First Class Mail shipping. DON'T buy them from Radio Shack!!

The second approach is a little more daring. Reassemble the boards so you can plug in the CCFLs. Don't plug in them all, just plug in one. Now turn on the monitor. Do you see a brief flash of light? If so, unplug that CCFL and plug in another into it's connector. Again, turn on the monitor and look for a brief flash of light. Continue testing one CCFL at a time. If every CCFL gives a brief flash, order a full set of caps as in approach 1. This MIGHT be an inverter problem, but it's not worth troubleshooting until you are sure the caps are good.

PlainBill

[mr.tight]

Re: LG1915S backlight problem

How is actually written on the chip? Like this?



It matters because it will help find the datasheet.

Bring on the testing! lol

It's written:

NIKOS
P2103NVG
G4549841

[mr.tight]

Re: LG1915S backlight problem

I think you may have two problems here. The slow startup is usually an indication of failing capacitors. The brief flash of light is usually caused by a problem with one of the CCFLs. 'Two seconds to black' can be caused by bad capacitors. It depends on the design of the inverter; sometimes they have a very short startup time. Samxon's are not known for high quality, but I am not aware if they are known to fail without physical signs.

I see two approaches. The first would be to replace every electrolytic cap on the power supply / inverter except the large 450 volt one. I count 9 caps, including the two small ones by the transformer. If you are in the USA this will cost about $10 - $12 from Digikey if you specify USPS First Class Mail shipping. DON'T buy them from Radio Shack!!

The second approach is a little more daring. Reassemble the boards so you can plug in the CCFLs. Don't plug in them all, just plug in one. Now turn on the monitor. Do you see a brief flash of light? If so, unplug that CCFL and plug in another into it's connector. Again, turn on the monitor and look for a brief flash of light. Continue testing one CCFL at a time. If every CCFL gives a brief flash, order a full set of caps as in approach 1. This MIGHT be an inverter problem, but it's not worth troubleshooting until you are sure the caps are good.

PlainBill

Thanks alot for reply.

You included the 'inverter' board, and i think there are 3 caps on there too? They look very different and dont have the cross on the top. I live in UK, but i do have a store nearby, i'll see if they have the full set tomorrow, or order them. When you talk of CCFL's, you are talking about the 2 connectors at each end? Just try all 4 in one socket?

I used to think it was temperature sensitive as it was only a matter of 1-2 hours and it would work, but yesterday it had 7 hours with the green light on and still wouldnt stay on. A problem that was developing, isnt a DEVELOPING problem more likley to be capacitors? Dont laugh, i know nothing...

[PlainBill]

Re: LG1915S backlight problem

Thanks alot for reply.

You included the 'inverter' board, and i think there are 3 caps on there too? They look very different and dont have the cross on the top. I live in UK, but i do have a store nearby, i'll see if they have the full set tomorrow, or order them. When you talk of CCFL's, you are talking about the 2 connectors at each end? Just try all 4 in one socket?

I used to think it was temperature sensitive as it was only a matter of 1-2 hours and it would work, but yesterday it had 7 hours with the green light on and still wouldnt stay on. A problem that was developing, isnt a DEVELOPING problem more likley to be capacitors? Dont laugh, i know nothing...

The inverter is on the power supply board. I refer to the other board is the logic board; a more accurate term would be 'video and control board', but that's a bit much.

From my point of view, the 'smoking gun' is the brief flash. That and the fact you can see a display tells me the logic card is working. The fact that the backlights flash briefly during as the computer boots confirms the problem is with the inverter. As resolution changes the logic card will momentarily switch off the backlight, then switch them back on.

As far as testing the CCFLS, try each one in it's 'normal' socket. If one does not flash it could be either the inverter or the CCFL. If that happens, try switching it to the adjacent socket.

There are a number of possible causes of this problem. Certainly a deteriorating cap is a possibility. Indeed, if it were in the 12V supply or the inverter that would explain the symptoms. Another possibility is a deteriorating CCFL, or a lead to a CCFL that is breaking down or arcing.
The only reason I am suggesting testing before replacing caps is I have never heard of a case where there was a progressive deterioration that did not include bulging caps.

By the way, Farnell is on common source of capacitors. Also, make sure they are low ESR rated for 105°C. I personally prefer Panasonic FMs, but the third link in my signature leads to a FAQ listing other brands.

By the way, the Service manual is available on elektrotanya.com

PlainBill