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Old 09-30-2010, 11:51 PM   #41
alexanna
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Default Re: inverter problem in LG 1934S LCD flatron

If your realy wanting to stock your tool box look at http://ccflwarehouse.com/
They have a good assorment of ccfl pig tails,pin connectors-terminal pins and I think the kapton tape is important. It's the yellow tape.
Al.
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Old 10-02-2010, 01:45 PM   #42
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Default Re: inverter problem in LG 1934S LCD flatron

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Originally Posted by alexanna View Post
If your realy wanting to stock your tool box look at http://ccflwarehouse.com/
They have a good assorment of ccfl pig tails,pin connectors-terminal pins and I think the kapton tape is important. It's the yellow tape.
Al.
Thanks for the tip; I may end up doing that if I start to see a number of these monitors with similar problems. I ended up paying $32ish (incl. shipping) for 4 CCFLs on eBay from an auction that specifically mentioned the model of my monitor, which works out to about $8/lamp (seems like a competitive price, and shipped from the US). Since I only ended up needing one, I have 3 spares now. I re-used the original yellow tape, but it would probably be a good idea to get some more if I end up doing this more often. Same is true of the metal foil tape (that stuff refuses to stick again after being peeled up).

I got my new CCFLs last night and replaced the one defective-looking lamp from the top pair (it had dark ends, and the return wire was loose). I'm not sure if it's possible to get away with not completely taking the reflector assembly apart, but I couldn't figure out how to do it. Either way, I soldered the new lamp in place, plugged it in, and it worked perfectly!

After doing the replacement, I was curious if I could measure current draw and voltage drop of the bad lamp using my case mod inverter. I know the measurement won't necessarily mean anything for math in a different circuit, but I thought it might be useful to spot a difference between lamps. I wasn't brave enough to hook my multimeter to the return end of the CCFL to measure voltage, but I did measure current into the inverter on the bad lamp and one of the new ones. The inverter used 473mA on both lamps after sitting for a few minutes, but the inverter used 437mA immediately when plugged in with the new lamp attached, and 455mA with the bad lamp attached. Looks like I might be able to use this trick in the future to pick out a bad CCFL if current through the inverter is different for one lamp in a monitor than the others.

I had one more question after finishing up - what do you do with old CCFLs? Can I treat my bad one like any other fluorescent bulb and take it to my local transfer station for recycling, or is there something special I should do with it since it contains mercury?

Thanks for all the help, everyone! I really appreciate it!
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Old 10-02-2010, 02:17 PM   #43
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Default Re: inverter problem in LG 1934S LCD flatron

Quote:
Originally Posted by stevenps View Post

I got my new CCFLs last night and replaced the one defective-looking lamp from the top pair (it had dark ends, and the return wire was loose). I'm not sure if it's possible to get away with not completely taking the reflector assembly apart, but I couldn't figure out how to do it. Either way, I soldered the new lamp in place, plugged it in, and it worked perfectly!

After doing the replacement, I was curious if I could measure current draw and voltage drop of the bad lamp using my case mod inverter. I know the measurement won't necessarily mean anything for math in a different circuit, but I thought it might be useful to spot a difference between lamps. I wasn't brave enough to hook my multimeter to the return end of the CCFL to measure voltage, but I did measure current into the inverter on the bad lamp and one of the new ones. The inverter used 473mA on both lamps after sitting for a few minutes, but the inverter used 437mA immediately when plugged in with the new lamp attached, and 455mA with the bad lamp attached. Looks like I might be able to use this trick in the future to pick out a bad CCFL if current through the inverter is different for one lamp in a monitor than the others.

I had one more question after finishing up - what do you do with old CCFLs? Can I treat my bad one like any other fluorescent bulb and take it to my local transfer station for recycling, or is there something special I should do with it since it contains mercury?

Thanks for all the help, everyone! I really appreciate it!
Congratulations on the successful repair.

Thanks for the information on the current draw from the case mod inverter with the bad CCFL. Altogether, a lot of useful information.

Standard florescent lights contain mercury, just like CCFLs (Cold Cathode Florescent Light). Take them to the transfer station.

PlainBill
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Old 10-07-2010, 01:54 AM   #44
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Default Re: inverter problem in LG 1934S LCD flatron

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Congratulations on the successful repair.
Thanks To close, I did the same check on the second of these monitors that I had, and replaced the same CCFL (the one with the blue/black wires on the top of the monitor). Same problem on the inside - return wire was loose, and there were scorch marks on the rubber end cap.

Thanks again for all the great assistance!
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Old 01-05-2011, 03:56 PM   #45
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Default Re: inverter problem in LG 1934S LCD flatron

thank you verry much for all this informations
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Old 01-12-2011, 06:05 PM   #46
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Default Re: inverter problem in LG 1934S LCD flatron

Hello people. I got one w1934s yesterday from a friend of mine, and he said to me that monitor just woun't turn on. I got it allready in peaces. I saw that the capacitor c506 is all black and around him too. in specification I've found that it is 10pF 3KV. I got one of those and have changed, but monitor still wount turn on. Can you give me some ideia what else can I check?
thnx
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Old 01-12-2011, 10:46 PM   #47
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Default Re: inverter problem in LG 1934S LCD flatron

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Originally Posted by ljubomir View Post
but monitor still wount turn on. Can you give me some ideia what else can I check?
1) With power off and lcd unplugged, check your fuses with a multimeter. A good fuse should measure less than 1.0 ohms.

2) Is the green power led on?

Report back and we can suggest more test points. Also, please state your experience in using a multimeter. For newbies, we can give explicit instructions. If you have a Fluke 87-5, then I will assume you are an expert.
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Old 01-24-2011, 08:06 PM   #48
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Default Re: inverter problem in LG 1934S LCD flatron

Hi guys, much searching and some testing and I'm a bit stuck. I have this monitor and the backlight goes out after a 2 seconds.

Here's what I've done so far:

I think I eliminated a bad CCFL by unplugging one at a time and turning it on. Same problem.

I've followed this flow chart in the service diagram and it all seems to check out.



I'm not sure if my results are any good though as I've not desoldered anything from the board, and I'm getting a 1.7ish volts reverse voltage on a couple of the diodes and transistor junctions.

Also when it said about instantaneous pulse I just stuck the dmm on dc and there was definitely some "pulsey" potential going on in there.

Am I going about this all the wrong way? Not done any electronics for quite a while and most of that was telecomms based.

p.s. I'm using a Fluke 25 I can get a 'scope from work but I'd rather not lug it home and set it up on the dining table if I can help it!

As an afterthought, I'm testing this with the CCFLs and the panel NC, is that going to put a spanner in my works? And there is no green light! I have a blue/orange one on the bezel but I thought there may be one on the PCB somewhere. Should there be?

Errr... I'm poking holes in my testing quite a bit here, I measured the inverter transformers just for resistance, they were the same and not a large number.

Last edited by woody_294; 01-24-2011 at 08:14 PM..
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Old 01-24-2011, 08:31 PM   #49
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Default Re: inverter problem in LG 1934S LCD flatron

Quote:
Originally Posted by woody_294 View Post
I think I eliminated a bad CCFL by unplugging one at a time and turning it on. Same problem.
The inverter will shut down if one lamp is not connected even if all the lamps work, as the inverter will "sense" there is a problem.

Post pictures of your boards ...
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Old 01-24-2011, 08:40 PM   #50
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Default Re: inverter problem in LG 1934S LCD flatron

Quote:
Originally Posted by woody_294 View Post
Hi guys, much searching and some testing and I'm a bit stuck. I have this monitor and the backlight goes out after a 2 seconds.

Here's what I've done so far:

I think I eliminated a bad CCFL by unplugging one at a time and turning it on. Same problem.

I've followed this flow chart in the service diagram and it all seems to check out.



I'm not sure if my results are any good though as I've not desoldered anything from the board, and I'm getting a 1.7ish volts reverse voltage on a couple of the diodes and transistor junctions.

Also when it said about instantaneous pulse I just stuck the dmm on dc and there was definitely some "pulsey" potential going on in there.

Am I going about this all the wrong way? Not done any electronics for quite a while and most of that was telecomms based.

p.s. I'm using a Fluke 25 I can get a 'scope from work but I'd rather not lug it home and set it up on the dining table if I can help it!

As an afterthought, I'm testing this with the CCFLs and the panel NC, is that going to put a spanner in my works? And there is no green light! I have a blue/orange one on the bezel but I thought there may be one on the PCB somewhere. Should there be?

Errr... I'm poking holes in my testing quite a bit here, I measured the inverter transformers just for resistance, they were the same and not a large number.


Welcome to the forum! There's a few things that need to be cleared up. First, like EGuevarae says, disconnecting one CCFL at a time only tells the CCFL controller chip that there's an open circuit and it will kill power to all the CCFL's. Ideally, you'd want to check the CCFL's by substituting a known good CCFL one at a time. With power off, disconnect one CCFL and connect the good one. Power up monitor. If it goes off then power down and try the next tube. Do this for all 4 tubes. If you get all 4 tubes to light, then you've found the bad tube.

Next thing, good flowchart. However, since we don't know what U501, U502, IC501, etc is, it makes it difficult to follow what's going on. This is why we request clear focused photos of the entire power board top and bottom.

Your problem can be caused by:

bad CCFL(s)
bad CCFL wiring
bad inverter transformer
bad CCFL controller or sense circuitry

Last edited by jetadm123; 01-24-2011 at 08:44 PM..
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Old 01-24-2011, 08:40 PM   #51
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Default Re: inverter problem in LG 1934S LCD flatron

What EGuevarae said. Also, retiredcaps has written extensively on troubleshooting '2 seconds to black' problems.

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Old 01-24-2011, 09:35 PM   #52
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Default Re: inverter problem in LG 1934S LCD flatron

2 seconds to black guide.

Start with post #13 and #14 at

http://www.badcaps.net/forum/showthread.php?t=10419
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Old 01-25-2011, 11:11 AM   #53
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Default Re: inverter problem in LG 1934S LCD flatron

Thanks guys for pointing me to all that useful stuff! I think I'll make much better progress when I get going this time!

For reference and any further questions I ask, some photos and info:

Also the ICs, IC501 is an OZ9938GN
U501 and U502 are both a P6006HV

I have the photos in a much larger resolution but I though 800px wide would be enough, let me know if it's not

Thanks again all, great replies!!
Attached Images
File Type: jpg board top crop800.jpg (373.0 KB, 93 views)
File Type: jpg board_bottom crop800.jpg (309.7 KB, 90 views)

Last edited by woody_294; 01-25-2011 at 11:15 AM.. Reason: Grammar!
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Old 01-25-2011, 03:52 PM   #54
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Default Re: inverter problem in LG 1934S LCD flatron

Quote:
Originally Posted by woody_294 View Post
Thanks guys for pointing me to all that useful stuff! I think I'll make much better progress when I get going this time!

For reference and any further questions I ask, some photos and info:

Also the ICs, IC501 is an OZ9938GN
U501 and U502 are both a P6006HV

I have the photos in a much larger resolution but I though 800px wide would be enough, let me know if it's not

Thanks again all, great replies!!

If you haven't done so, try measuring the resistance across the inverter transformer secondaries (marked 7 and 8 on the circuit board) for transformers T501? and T502? Should be no more more than 3% difference in your readings.
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Old 10-29-2011, 02:57 AM   #55
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Question Re: inverter problem in LG 1934S LCD flatron

Hi,

I have the similar problem with the monitor mentioned it the first post of this thread LG Flatron W1934S.

Few days ago it suddenly went black while the blue light still lit indicating that it is turned on and connected to power and video source. I tested it with different cable and different machine, different OS, but the result was the same. So it is definitely a monitor problem.
In detail:
After turning the monitor on it goes fine for about 15-20 min. and then goes black. It usually goes black when bright colors are displayed. Also I noticed that when I set brightness (in the monitor settings) to the lowest value, it will work then for 1 to 3 hours. But after that it still goes black with blue light at the bottom still shining. Then if I turn it on again it displays for a few seconds flashes (bright, low bright and again bright) and goes black again. If I wait about 20 mins I can use it again for 1 to 3 hours at lowest brightness.

I think it could be a component that heats up too much and then shuts off. I haven't tried to take it apart yet.

So I am waiting for any help anyone can offer.
Thank you in advance
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Old 10-29-2011, 07:48 AM   #56
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Default Re: inverter problem in LG 1934S LCD flatron

Quote:
Originally Posted by younio View Post
Hi,

I have the similar problem with the monitor mentioned it the first post of this thread LG Flatron W1934S.

Few days ago it suddenly went black while the blue light still lit indicating that it is turned on and connected to power and video source. I tested it with different cable and different machine, different OS, but the result was the same. So it is definitely a monitor problem.
In detail:
After turning the monitor on it goes fine for about 15-20 min. and then goes black. It usually goes black when bright colors are displayed. Also I noticed that when I set brightness (in the monitor settings) to the lowest value, it will work then for 1 to 3 hours. But after that it still goes black with blue light at the bottom still shining. Then if I turn it on again it displays for a few seconds flashes (bright, low bright and again bright) and goes black again. If I wait about 20 mins I can use it again for 1 to 3 hours at lowest brightness.

I think it could be a component that heats up too much and then shuts off. I haven't tried to take it apart yet.

So I am waiting for any help anyone can offer.
Thank you in advance
Take the %#@#%*%#@ monitor apart!!! See if there are any obvious problems. If there are not, take good pictures of the top and bottom of the power supply and attach them to your next post using 'Manage Attachments' - below the text entry area.

There are a number of possible causes, none of them are going to get fixed without taking the monitor apart.

PlainBill
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Old 10-30-2011, 05:12 AM   #57
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Default Re: inverter problem in LG 1934S LCD flatron

Quote:
Originally Posted by PlainBill View Post
Take the %#@#%*%#@ monitor apart!!! See if there are any obvious problems. If there are not, take good pictures of the top and bottom of the power supply and attach them to your next post using 'Manage Attachments' - below the text entry area.

There are a number of possible causes, none of them are going to get fixed without taking the monitor apart.

PlainBill
Thanks.

Ok. I have disassembled the monitor. It was a bit tricky to open it up even after looking at the service manual. So, the board seems to be without any visible damage.
I have already looked through the troubleshooting guide from the "jetadm123" post. I noticed then, that the 2nd pin of IC501 has not 5Vdc but 6.6Vdc. Is this normal? If not then what should I do next?
If it is normal then I faced another problem. I checked the pin10 of IC501 for high level voltage? it is 4.2Vdc. The thing is that I am not sure what "high level" actually means
Attached Images
File Type: jpg upper.JPG (1.47 MB, 52 views)
File Type: jpg bottom.JPG (1.50 MB, 46 views)
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Old 10-30-2011, 08:05 AM   #58
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Default Re: inverter problem in LG 1934S LCD flatron

Quote:
Originally Posted by younio View Post
Thanks.

Ok. I have disassembled the monitor. It was a bit tricky to open it up even after looking at the service manual. So, the board seems to be without any visible damage.
I have already looked through the troubleshooting guide from the "jetadm123" post. I noticed then, that the 2nd pin of IC501 has not 5Vdc but 6.6Vdc. Is this normal? If not then what should I do next?
If it is normal then I faced another problem. I checked the pin10 of IC501 for high level voltage? it is 4.2Vdc. The thing is that I am not sure what "high level" actually means
While the pictures aren't great, they are good enough to confirm the caps LOOK good; of course appearances can be deceiving. They probably aren't the problem because of the time lapse between initially turning the monitor on and the backlights failing.

I'm afraid the next most likely suspect is the CCFLs, but let's try an easy test first. T501 and T502 are the inverter transformers. Pins 7 and 8 are the secondaries on each one. Measure the resistance between pins 7 and 8 of T501 and between pins 7 and 8 of T502. They should be about 1K, and must match to within 3%. Report the numbers.

I'll look up the information on the voltages at IC501. That may well be a clue as to what is going wrong.

I just reviewed the schematic; that clears it up slightly. Pin 2 is the Power pin of IC501, pin 10 is Enable. In this context 'high' means 2.2 volts or higher. The problem is the troubleshooting guide covers NO backlights, you have a variation of 'two seconds to black', so we know most of the test points (Power, Enable, are good).

One additional simple test. Does the screen have a pinkish tint when it is first turned on, particularly if it's been sitting off for more than an hour? This tint may last for only a few seconds.

PlainBill

Last edited by PlainBill; 10-30-2011 at 08:22 AM..
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Old 11-26-2011, 07:17 AM   #59
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Default Re: inverter problem in LG 1934S LCD flatron

hi all I am only using a dmm.... I need some help in measuring an LG flatron 1710 inverter voltages..... From the schematic the voltages are on the 1KV range.... Did anyone measure them? I want to trouble shoot my inverter...... so far I have found that the U501, and U502 are shorthed.... Help please...
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Old 11-26-2011, 08:24 AM   #60
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Default Re: inverter problem in LG 1934S LCD flatron

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hi all I am only using a dmm.... I need some help in measuring an LG flatron 1710 inverter voltages..... From the schematic the voltages are on the 1KV range.... Did anyone measure them? I want to trouble shoot my inverter...... so far I have found that the U501, and U502 are shorthed.... Help please...
The output voltages of the inverter are in the order of 1KV at 40 Khz. That is beyond the normal capabilities of a DMM, and trying to measure it can kil a DMM.

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