LG1915S backlight problem

[mr.tight]

Re: LG1915S backlight problem

oh, and email me on nikijb@live.com if you have same problem, and i'll send you the set of caps (in the UK). I probably wont have any use for 21 caps now.

[mr.tight]

Re: LG1915S backlight problem

Excuse my language........IT F**KING WORKED!!


I thought id messed it up though, when soldering. I accidentally joined over to some solder strip about 2 cm long. I dont know what their job is, but i did my best to seperate them again, but still wasnt 100% happy. Tried it anyway, and came on immediately!

I searched for many links on this problem, and no thread had a proven solution, until now. I hope others will find this thread that have the same problem. Thanks Plainbill for giving me the incentive, and thanks to others that showed an interest.

£20 quid well spent!

Lets re-assemble it and hope it stays that way now.

[mr.tight]

Re: LG1915S backlight problem

well, the caps arrived today, costing me £20. (Packs of 5 only)
In the next couple of hours i will be soldering them on. Please keep your fingers crossed for me, and perhaps you might want to place your bets now. Im going for a 30% success rate.

I hope this works and makes this thread very usefull to others in the future.

[mr.tight]

Re: LG1915S backlight problem

Just don't try replacing the caps while the monitor is plugged in.

ok, i will try not to, although its tempting.

be in touch

[PlainBill]

Re: LG1915S backlight problem

Thankyou PlainBill. I will post my results in a few days. It would be nice if this symptom was fixed with a capacitor change. Just one last question for now: When i remove the old capacitors, is it right that i have to short them with a screwdriver?

No. If the power supply is working (and yours is), it will discharge the large cap down to about 20 volts. The small caps will discharge normally within minutes of the power cord being unplugged.

Just don't try replacing the caps while the monitor is plugged in.

PlainBill

[mr.tight]

Re: LG1915S backlight problem

Here's what I came up with. These are the Panasonic part numbers. They should apply to any supplier. I can't come up with a compatible

2x 1000uf 16v EEUFM1C102
1x 1000uf 25v EEUFM1E102
2x 680uf 25v EEUFM1E681
1x 470uf 25v EEUFM1E471
2x 33uf 50v EEUFC1H330

And the last is a Nichicon part.

UPW1HR47MDD

For the service manual, try this link.

PlainBill

Thankyou PlainBill. I will post my results in a few days. It would be nice if this symptom was fixed with a capacitor change. Just one last question for now: When i remove the old capacitors, is it right that i have to short them with a screwdriver?

[PlainBill]

Re: LG1915S backlight problem

Congrats on learning something new
I did do electronics at college, but ive forgotten so much. At least i walked away with the ability and courage to solder. Can he replace that CCFL, or will he buy new?

Can i have your help with the caps please? Ive looked at some uk sites selling panasonic caps all except the 0.47uf 50v, but another site has it. When i was looking at them, there were a couple that had slightly different names. These are panasonics, which ones should i go for?

http://uk.rs-online.com/web/search/s...016+4294626541

I need:
2x 1000uf 16v
1x 1000uf 25v
2x 680uf 25v
1x 470uf 25v
2x 33uf 50v
1x 0.47uf 50v

I could not find the service manual in that link. I would be really really gratefull to you, Plainbill, if you could confirm the exact ones i need for my monitor. Im bound to make a mistake if left unguided.

your hopefully
Nick

Here's what I came up with. These are the Panasonic part numbers. They should apply to any supplier. I can't come up with a compatible

2x 1000uf 16v EEUFM1C102
1x 1000uf 25v EEUFM1E102
2x 680uf 25v EEUFM1E681
1x 470uf 25v EEUFM1E471
2x 33uf 50v EEUFC1H330

And the last is a Nichicon part.

UPW1HR47MDD

For the service manual, try this link.

PlainBill

[mr.tight]

Re: LG1915S backlight problem

im going to leave the monitor on until i get the caps. If i pull the vga lead out, i think the OSD just dances around the screen indefinitely. I dont think that would use much power would it? The weather is mild at the moment, and i cant help thinking this is why its working right now.

[mr.tight]

Re: LG1915S backlight problem

Congrats on learning something new
I did do electronics at college, but ive forgotten so much. At least i walked away with the ability and courage to solder. Can he replace that CCFL, or will he buy new?

Can i have your help with the caps please? Ive looked at some uk sites selling panasonic caps all except the 0.47uf 50v, but another site has it. When i was looking at them, there were a couple that had slightly different names. These are panasonics, which ones should i go for?

http://uk.rs-online.com/web/search/s...016+4294626541

I need:
2x 1000uf 16v
1x 1000uf 25v
2x 680uf 25v
1x 470uf 25v
2x 33uf 50v
1x 0.47uf 50v

I could not find the service manual in that link. I would be really really gratefull to you, Plainbill, if you could confirm the exact ones i need for my monitor. Im bound to make a mistake if left unguided.

your hopefully
Nick

[PlainBill]

Re: LG1915S backlight problem

just to add...
Ive just spent a couple of minutes pressing the power button, and its decided to come back to life. Its now on, but still in pieces. Im relieved about that as i thought i might had damaged something yesterday with that unsavoury noise i heard. So at least im still only dealing with this one problem. Now, im going to put it back together, (while its on!) because i would like to use it this evening. (getting neck-ache looking at tv)

I honestly don't know. I just completed a marathon session with another person who had a classic 'two seconds to black' problem. After extensive troubleshooting an a tremendous effort on his part he discovered that he had a bad CCFL. When he compared the old and new CCFLs he discovered they both drew the same current after they had been on a for 10 seconds or more, BUT the bad one drew significantly more in the first few seconds.

That might explain the behavior of your monitor.

I learned something new today!

PlainBill

[mr.tight]

Re: LG1915S backlight problem

just to add...
Ive just spent a couple of minutes pressing the power button, and its decided to come back to life. Its now on, but still in pieces. Im relieved about that as i thought i might had damaged something yesterday with that unsavoury noise i heard. So at least im still only dealing with this one problem. Now, im going to put it back together, (while its on!) because i would like to use it this evening. (getting neck-ache looking at tv)

[mr.tight]

Re: LG1915S backlight problem

Hello guys.

Well, i spoke again about caps with 'Maplins' (a uk store), and when i asked about whether or not they are branded and reputable, the answer was no. Some of them have some sort of brand name, but they arent all the same. I find that odd, that one of the few places one can buy components, they decide to sell cheap ones. Why would they not sell quality? Anyway, he wasnt saying they were rubbish, but id rather listen to your advice, than his. Why wont these caps work? If they wont do the job, then who are they selling these components to and what for?

I will have to phone around and see if any places sell good ones, but i suspect i may need to order them online, which will be days

However, before i do that, i have another observation.
Plainbill, you asked me what happens if i hook up two connectors on the same side? Well, i get a flash of the screen. I hooked up the vga lead so i had a proper image to look at. If i hook up one lead, i get a dim screen for exactly 1 second. If i hook up two on same side, i get a flash. However, if i hook up 3, i get the screen for 1 second, then finally with all 4 plugged in, back to a flash.

Is this still looking like bad caps? If so, i will order them tomorrow and go with a brand you recommend.

Many thanks.

[pedro]

Re: LG1915S backlight problem

The good news is, the local store sells most of the capacitors i need, but i guess i still need good reason to go ahead with that.

I don't know who/what your "local store" is. I hope you have taken on board the important advice about using only good quality (aka reputable brand/series) 105C low-ESR caps, not generic electros which will as a rule NOT fulfill the required function, let alone last the distance.

[PlainBill]

Re: LG1915S backlight problem

p.s. I only tested them quickly, as there was no video signal, then there wasnt anything to see apart from the initial 1 sec OSD.
Im very willing to start testing more, now this is becoming a mission

There are several possibilities - the caps on the inverter supply lines are bad, allowing excess ripple. The situation is worse when all CCFLs are drawing power, hence the quick shutdown. Another possibility is the CCFLs are drawing too much power, causing the shutdown.

The only other test I could suggest is to hook up two CCFLs on the same side and see what happens.

The best advice I can give at this point is to replace the caps in the power supply. Certainly the symptoms sound like deteriorating caps. But unlike the cases when I open up a monitor and find half a dozen vented caps, I'm not sure that is the problem.

PlainBill

[mr.tight]

Re: LG1915S backlight problem

p.s. I only tested them quickly, as there was no video signal, then there wasnt anything to see apart from the initial 1 sec OSD.
Im very willing to start testing more, now this is becoming a mission

[mr.tight]

Re: LG1915S backlight problem

One of the problems with 'remote troubleshooting' is understanding what is happening. It is normal for the display to be dimmer when only one CCFL is plugged in. It is a good sign they all worked. I am curious about the length of time they were on for each test. When only one CCFL was hooked up you reported seeing an OSD. How about when you had all of them plugged in? I was under the impression they were on only for a small fraction of a second.

If the time duration is the same in all cases, I would replace the capacitors. It is likely to fix the problem; certainly it is the easiest step.

PlainBill

HI, thanks for replying.

It is a good sign they all worked

But what about the first test where the blue/black leads (in their correct socket) produced an unhealthy sound and image?

How about when you had all of them plugged in?

Then im back to a flash. (literally, a flash)
It is only when i connect them one at a time, i get the dim OSD, but this lasts for about a second. Seeing as there is no video signal, i only get to see the OSD, but i think 1 second is the correct amount of time.

Im concerned why it made that noise the first time around, (with the corrupt OSD), could that be to do with the caps? I really hope it is the caps, as i feel confident enough to replace them. I dont want to replace them unless you guys genuinely feel it would fix it.

Thankyou,

[PlainBill]

Re: LG1915S backlight problem

Dont you hate it when you type a post only to hit the wrong button and accidently close the page? Grrrrrr.

The long and short of it was...

I tested the leads, then tested again some minutes later, but had different results.

The blue/black leads are furthest in, with the grey/black leads towards the edge. There was an issue when plugging in the blue/black lead which briefly showed a fuzzy OSD with a static noise from the board. That happened on the opposite end too. Plugging that lead in the socket next to it, just produced a dim OSD (for the correct amount of time i believe) The grey/black leads just resulted a brief OSD no matter what socket i put them in. The second time around, i couldnt repeat the fuzzy OSD with the noise; i was getting a dim OSD everytime. Its so fiddly to plug and unplug them as the screen needs to plugged in too, leaving me very little room. Anyhow, the results are inconlusive im afraid. I connected all the leads back up, and it flashed as 'normal', but not dim.

The good news is, the local store sells most of the capacitors i need, but i guess i still need good reason to go ahead with that. Im happy to test again, but perhaps i need step-by-step instructions.

I eagerly await your assistance.

Many thanks
Nick

One of the problems with 'remote troubleshooting' is understanding what is happening. It is normal for the display to be dimmer when only one CCFL is plugged in. It is a good sign they all worked. I am curious about the length of time they were on for each test. When only one CCFL was hooked up you reported seeing an OSD. How about when you had all of them plugged in? I was under the impression they were on only for a small fraction of a second.

If the time duration is the same in all cases, I would replace the capacitors. It is likely to fix the problem; certainly it is the easiest step.

PlainBill

[mr.tight]

Re: LG1915S backlight problem

Dont you hate it when you type a post only to hit the wrong button and accidently close the page? Grrrrrr.

The long and short of it was...

I tested the leads, then tested again some minutes later, but had different results.

The blue/black leads are furthest in, with the grey/black leads towards the edge. There was an issue when plugging in the blue/black lead which briefly showed a fuzzy OSD with a static noise from the board. That happened on the opposite end too. Plugging that lead in the socket next to it, just produced a dim OSD (for the correct amount of time i believe) The grey/black leads just resulted a brief OSD no matter what socket i put them in. The second time around, i couldnt repeat the fuzzy OSD with the noise; i was getting a dim OSD everytime. Its so fiddly to plug and unplug them as the screen needs to plugged in too, leaving me very little room. Anyhow, the results are inconlusive im afraid. I connected all the leads back up, and it flashed as 'normal', but not dim.

The good news is, the local store sells most of the capacitors i need, but i guess i still need good reason to go ahead with that. Im happy to test again, but perhaps i need step-by-step instructions.

I eagerly await your assistance.

Many thanks
Nick

[mr.tight]

Re: LG1915S backlight problem

Thanks for that wealth of info.

I will report back the results from CCFL testing tomorrow.
Are you certain those caps look ok in the pictures? The short one out of the 6, looks flatter than the taller ones. Ive made a note of all the caps i need and have taken onboard what you recommended. If its the CCFL's, then is it still worth repairing?


thanks to all.

[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