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CCFL problem

exoticasian30

Mar 3, 2010
4
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Mar 3, 2010
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Hi there,

I wonder if you could advise me on a ccfl tube problem?

I have a dell inspiron 8600 laptop with a 15.4 wuxga screen and the ccfl tube stopped working. After asking for some advice, I replaced the independent inverter with a new one but still nothing so I stripped out the ccfl tube.

I plugged the inverter and ccfl tube back in, independent from the lcd screen so I could see what was going on and I found that the tube lights up for just a split second when I power on the laptop. Then nothing. This will happen every time the laptop is restarted, just a brief, split second flash from the tube which is around 5 years old.

I am currently using a second desk standing lcd through a vga cable and that works perfectly so I guess my graphics card is fine?

Can you comment on what you think the problem may be?

Many thanks in advance,

Paul
 

55pilot

Feb 23, 2010
434
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Feb 23, 2010
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CCFL inverters have open bulb and short circuit protection. One or the other is getting triggered on your new inverter.

I am missing one critical point. How was your original inverter behaving in death? Did it stop working completely or was that one flashing too?

If the symptoms were exactly the same with your original inverter as the new one, then the problem is in the tube or the wiring. Inspect the wiring for cracked or pinched insulation. The strike voltage can be over 1,000V and at that voltage even a tiny crack in the insulation can arc to the chassis and the stray current will cause the controller to see a short circuit and shut down.

Finally, CCFL bulbs do go bad. They have a life expectation of about 35,000 hours of use. That means that on average they will live that long, but it also means that some will die sooner. As CCFL lamps age, the strike voltage increases and the inverter will eventually not be able to generate enough voltage and the open lamp safety will kick in, even though the lamp is starting to strike.

Though very rare, it is possible for the lamp to leak over time. That one would be based on the 5 years of elapsed time (as posed to active time). The failure mode once again is requiring a higher strike voltage.

Where did you get the new inverter? Are you sure that it is a good inverter and not one out of a system that was having the same symptoms you are seeing? If you bought it on eBay, that is a very common scam (buy a new part and sell your old parts without saying that they do not work). Is the new inverter the EXACT same model? The longer the tube, the higher the strike voltage. There may be a family of inverters with different strike voltages and maximum currents and you may have ended up buying one that does not have a high enough voltage or high enough current.

Edited to add: The inverter on smaller screen Dell laptops is not the same as the inverter on larger screen laptops. This is due to the difference in voltage/current for the larger/smaller bulb. If you bought a generic "Dell laptop inverter" you may have gotten one that is not up to the task.

---55p
 
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exoticasian30

Mar 3, 2010
4
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Mar 3, 2010
Messages
4
Thanks for taking the time to reply 55pilot,

I was not too sure how my original inverter was behaving in death as it was still encased in the laptop to be honest but this is how the sequence has gone since then.

Stripped out the ccfl.

Plugged it back into the original inverter and layed it to one side, away from any metal casework.

Restarted computer and got a split second, bright flash from the ccfl.

Purchased a secondhand (supposedly tested and working) inverter from ebay. Original part with number (LTN154P/U-B) (K02I056.01).

Plugged in this 2nd inverter, started computer and get a split second, bright flash from the ccfl.

I asked the seller if he could confirm the part as working and he did. He has a very good feedback rating which was all I could judge by to be honest. He also sent me out another inverter to try, just incase. This is also secondhand, original and same part number etc.

So now I have three inverters!

Plugged in this 3rd inverter, started computer and get a split second, bright flash from the ccfl.

I have gone ahead an ordered a new ccfl (334mm by 2mm).

I would have thought I would have to be pretty unlucky to have three inverters all behaving badly although what you mentioned about ebay has worried me.

I was going to attemp testing the output voltage from the inverters but 1500 volts kinda worries me!

So at the moment, I've got my fingers crossed that I can fit the new ccfl without breaking anything...

Thanks again for your time,

Paul
 

55pilot

Feb 23, 2010
434
Joined
Feb 23, 2010
Messages
434
You have done a pretty good job of isolating the problem to the CCFL bulb or its wiring. You still need to take a close look at the high voltage wiring and the connector. In addition to a break in the insulation (unlikely if it is away from anything conductive) you also need to worry about the condition where the conductor has broken at the hinge bend point while the insulator is still intact over the break. In this case, the arcing is happening inside the wire. Same could be happening at the connector.

The 1500V happens for a few cycles only, but it is dangerous. You can not measure it with a multimeter or even a standard scope. You need a special high voltage 100:1 scope probes.

Check out the cables and if nothing is found, report back when you get the bulb. It will not be easy, but it will be doable.

Good luck.

---55p
 

exoticasian30

Mar 3, 2010
4
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Mar 3, 2010
Messages
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A new tube seems to have fixed it in some strange way.

I soldered up the new tube and removed all the shrink wrap from the existing cabling to check for any shorts. That seemed to be ok visually. I suspected it would be as I am one of those people who rarely moves his laptop or changes the position of the lid/screen.

I plugged the new tube into the inverter before fitting it back into the lcd display casing to check if it was going to work. It did the same thing as the old tube. Just a brief flash of light again on start up.

I was feeling pretty deflated by now and decided to just fit everything back together again, leave it inoperable and put it down to experience.

The funny thing was that once the lcd was reassembled and bolted back up the the lid casing, the bulb worked perfectly!

I cannot explain what I might have done. The only thing I can think of is that on every occasion previously I had plugged the ccfl into the inverter for testing, I failed to have the lcd screen plugged into the wiring ribbon.

Maybe the inverter can sense if the lcd screen is plugged in or not?

Anyway, somehow I'm back up and running which is a big relief on my wallet!

Thanks, pilot. You have been a great help and I really do appreciate you taking the time to advise me.

Paul
 

55pilot

Feb 23, 2010
434
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Feb 23, 2010
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434
You are welcome.

Intel chipsets do have a backlight enable output that is connected to the inverter to implement sleep states. It is possible that they have implemented some means of detecting if the LCD is working and when the graphics driver realizes that the display is not working it it shuts down the backlight.

I would be hard pressed to believe that they are keeping the EDID data in the display and not hard coding it in the ROM, but maybe that is how they are doing it to support multiple display resolutions. In that case, it is possible that when the BIOS goes to enable the LCD it powers up the backlight, then goes looking for EDID, not find it and shut down the entire LCD system including the backlight.

Otherwise, what you are describing also fits the symptoms of a cable problem. You bent the cable to put it back together and it started to work. Don't be surprised if it stops working after a while, if that is the case.

In any case, I am glad you got it to work with a new inverter and a new bulb.

Congratulations.

---55p
 

exoticasian30

Mar 3, 2010
4
Joined
Mar 3, 2010
Messages
4
I think you may have a good point regarding the cabling. I'll be sure to keep a close look on that if the same problem returns.

Many thanks.
 

whiteoutage

Jul 20, 2017
108
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Jul 20, 2017
Messages
108
I think you may have a good point regarding the cabling. I'll be sure to keep a close look on that if the same problem returns.

Many thanks.


Old thread but common problem. For me it was a burnt out ccfl bulb. Usual repair is replace whole screen laptop panel assembly. While difficult, a bulb can be repaired but cost savings may be negligible especially in older laptops. Here is a link for an excellent tutorial on DIY ccfl bulb replacement: if you dare to.

http://www.laptoprepair101.com/replace-laptop-backlight-ccfl-lamp/

Clean work space, exact size bulb replacement, and lots of patience are all required. Special tape(both strong thin sticky and double sided tape) if you damage tape while removing. The problem you are facing is getting it back together with no light bleeding along the edges caused by improper repair. The bulb is contained inside a very delicate metal foil reflector shield that can not be damaged.

From memory a few years ago, my experience turned out usable with noticeable light bleeding on bottom of screen. This was caused by replacement ccfl being just slightly different. It was both a tad longer causing the ccfl to bow, and rubber end pads on bulb were a bit thicker which caused a bulge so the metal frame "clips" did not snap back in place thereby distorting the metal foil.

Originally these panels were made with precision machines assembling them perfectly every time, not designed with repair in mind.

The panels are so cheap on eBay etc., so the only time I would recommend this repair is if you happen to have a known good identical bulb lying around or used panel can not be procured.
 
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