I’ve had a Dell Latitude C840 for the past 4+ years now. It’s big and heavy, but I absolutely love the 15″ UXGA display at 1600×1200 resolution. It’s crisp and readable and bright. Until, of course, this past Thanksgiving weekend, when it went dead.
At first, I didn’t know what broke and in opening up the laptop, I managed to break a few of the delicate traces on the flex cable that connects the display to the video card on the laptop. A quick search of eBay turned up a replacement for $15. That arrived yesterday and replacing it was easy. Reconnecting the display, I discovered that there was an image on the LCD, but it was completely dim–no backlight, at all. In a sense, this is good news: an entirely new display assembly goes for $150-$200 on eBay, but the display itself is okay. The problem could either be in the CCFL (lamp) or in the power inverter.
How is this good news? The specific display I have is the Samsung LTN150U2-L02, and according to lcdpart.com, the suitable replacement CCFL is model MS20305, $9.99 (plus $9.99 shipping). Of course, the lamp could be just fine and it could be the backlight inverter that’s busted, which could be replaced by Ambit J07.027.P.00 for $39.99 (plus $9.99 shipping). (Note: The inverter that’s currently on the display is labeled “AMBIT REV:2 K02I051.00” and “LTN150U2-B”.) Both amount to less than the replacement of the display assembly, of course.
The downside here is that there’s no easy way (that I can think of) to test whether it’s the CCFL or the inverter that’s gone bad–or, worst case, both. Laptop Freak had a similar idea, trying to test the inverter with a multimeter, but the output from an inverter is typically in the range of 1,500 VAC which is both dangerous and outside the range of the average multimeter. The folks at Endicott Research Group published a great whitepaper on backlight inverters: Design Issues in the Selection of Backlight Inverters (PDF). In it, they explain how CCF’s work and how they test backlight inverters and how sensitive the tolerances are for proper operation. I’m guessing it’ll be cheaper to buy a replacement CCFL and hook it up to the inverter to see if it works than it would be to fiddle with the inverter and risk breaking it in the process.
Throughout all of this, I kept trying to think of people I knew who were hardware geeks who could help me troubleshoot this and I realized: as many online communities that I’m a part of and as many people I know, I don’t know any hardcore hardware geeks. I mean, I know plenty of folks who fiddle around and delve deeper than your average “I’ll just buy it at (insert electronics chain store name)” consumer, but that’s about it. In the upcoming year, I think I know what kind of new friends I want to make. :-)
Tags:
Dell C840,
LCD,
repair,
CCFL,
backlight inverter
Programmer, husband, father, singer, guitarist, tinkerer, reverse engineer, strange, and living in New Jersey. 
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Very inportant is lamp diamerter and lenght, if you can tell us the exactly figure for length and diamerter, OVL and supply all kind of ccfl lamps.
In this case, when you can see an faint image on the screen but there is no backlight, I would try replacing the screen inverter. Most likely that’s a problem.
Inverters are cheap, easy to replace and you have a good chance to fix the backlight problem.
Here’s an example of replacing screen inverter on an IBM notebook.
Laptop Repair Tech: I actually did replace the inverter first (hoping to avoid having to replace the CCFL). No luck–it was definitely the CCFL.
I chickened out on replacing the CCFL: rather than replace the CCFL, I just went and bought a whole new display assembly from eBay, for around $150. The time it would have taken to carefully replace the CCFL wasn’t worth it if I could just get a new assembly for $150.
Dossy,
I understand you. Replacing the CCFL tune is not an easy task, because you have to disassemble the laptop screen completely. Even experienced laptop repair technicians avoiding this job. Actually $150 is a great price for a new LCD screen.
Just recently I had to fix a laptop screen with water damage, I had to disassemble the LCD screen. It wasn’t very easy. If you have no experience fixing laptops, do not do that. You can easily damage the screen.
Right now I have another laptop. The laptop itself works fine, but the CCFL tube is bad. A new screen will cost me over $300 – it’s over the value of the laptop. Probably I will try to replace the CCFL tube myself (never done it before). I’ll create a disassembly guide for this project, so other people can see how difficult it is. :)
Hi All,
Thanks for a very interesting article. Have a similar problem myself. Symptoms – Power Laptop on, screen flashes normal brightness for a split second, then goes dark, but still functions, as can be seen if you shine a light onto it. I bought a new CCFL (http://www.jkllamps.com/) and have ordered a used but functioning inverter (www.eBay.com). I found the laptop “Dell Inspiron 510M” in someone’s trash and so I decided that it would be a fun project to fix it, so I’m not scared of doing further damage. I have also ordered a transformer for the presently non-functioning inverter.
My repair will be as follows:-
1 –
I will attempt to solder a new transformer component into the existing Inverter board. These can be purchased for £5 from http://www.lcdinverter.co.uk/coils.htm
2 – Failing this, I will try using the inverter I purchased
3 – Failing this, I will attempt to replace the CCFL by disassembling the LCD screen – a last resort, which I’m not really wanting to do.
The only reason I’m doing these things myself is because I have no time pressure to do a repair, and it’s costing a max of
Transformer – $8
Inverter – $20
CCFL – $15
Postage – DK – $30
$73 instead of $150 (+$40 postage) for a replacement LCD with inverter.
I will, of course update this blog once I have completer the repair and let you know what I had problems with. (and how hany CCFLs I snapped in the process ;)
Another good sight:-
http://iantha.vectorstar.net/ccfl.html
in my opinion it is foolish to repair laptops because in the market good laptops are available for cheap prices so why waste money on repairs!!!!
i would like people to comment on this issue cauz no one has yet commented after me
Tracy: Until replacement laptops are as cheap as–or, at least within 30% of the cost of–repairs, people will continue to repair laptops.
Also, it’s a factor of quality: newer laptops are cheaper, but their quality reflects their lower price. My Dell C840 has a gorgeous 15″ standard aspect ratio (4:3) 1600×1200 screen. Modern laptops all have much lower resolution widescreen displays.
well i agree to you to an extent but the changing trend in the market is actually moving towards disposing off things once they are gone bad
Well I would agree with Tracy anways ……laptops are not cheap because of poor quality always….find a better vendor and he might tell you….I personally myself bought a Dell Lattitude D600 ….it’s affordability plus comfort, and I’m in love with it !
refurbished computers is what i would want you to experience ….
I see that a few people posted what they are going to do to fix their laptops, but no updates to let us know what happened. I too have the same problem with my C840 (there is an image but no backlight).
And to answer why we would fix our old junk… Duh, because its fun.
Don: Alas, I’m ashamed to admit that I decided to not replace the CCFL in the display–too much effort involved–and just bought an entire replacement display assembly off eBay.
I do still have the old display in my parts closet, and some day I will buy a CCFL and do the replacement – but for now, I just needed to get my laptop working and went for the quick and easy fix.
Well it certainly could be fun to fix your laptops if you see it that way
That’s absolutely true , it’s not necessary that all used computers are junk i am into refurbished products and why not if they are in perfect working condition.