CCFL replacement for LTN141P4-L02

[tadejr]

Hello, everyone.

Some time ago I posted here asking for help re. a failing backlight in my T61 (14.1", SXGA+) and was advised to try finding a T6x to act as a donor. I eventually found a cheap T60 (malfunctioning motherboard/graphics) with the same panel type and swapped the panel. I hoped to be able to relax for a while, but the dreaded red hue on display startup, low brightness and occasional noise from the inverter is also present on this other panel; I expected the panels to be hit and miss at this age, so I'm not too disappointed. The T60, apart from the motherboard, is a fine machine and I hope to fix it eventually.

Most importantly, however, I bought a little time, so I can at least use the computer AND I now have a spare panel to fiddle with. Time to get that CCFL replaced.

I'm thinking of getting the backlight from here: http://backlightweb.co.uk/index.php?mai ... ucts_id=96

The same shop also offers a replacement kit: http://backlightweb.co.uk/index.php?mai ... ducts_id=8

Would you recommend I also get this kit? Apart from what they simply call "wires" and "ends" (I can't figure out what exactly they mean), all of the stuff contained within is standard off the shelf stuff, presumably cut to size. Getting a set of CCFL bulbs (2 of them... in case you break one?) along with the kit is still pretty cheap though, in comparison to the alternatives, at around 16 €.

I know the CCFL replacement is a handful, but I'm ready to attempt it now.

There are instructions for many different panels here, but sadly none for mine (LTN141P4-L02):
http://www.lcdparts.net/howto/instruction/ICCFL1.aspx
I've taken a look at some of them for LTN141[...] panels, which are the same size and they all look fairly similar in the way they are built, so I imagine there isn't all that much difference.

What do I have to be most careful about? Does anyone have any experience or suggestions?
I'm thinking of maybe getting an anti-static wrist strap (I've been meaning to get one for a while), although I can't imagine the bulbs to be all that sensitive to static discharges in comparison to ICs. I also have a 30W soldering iron with a conical point, which seems like it might be too much, but hopefully if I'm careful it shouldn't be a problem.

Another question on my mind is about whether to also replace the inverter. The noises in mine are barely noticeable and very occasional, whereas the one from the T60 I bought and scavenged the panel from sounded pretty bad (plus the screw holes don't line up with the mounting points in the screen cage).

Okay, that's a lot of stuff, thanks in advance for any help. Cheers!

EDIT:
ahh, the "2 x 290 mm" means a 2 mm diameter bulb, not two bulbs. I thought that was a bit weird... that site is hardly a jewel of clarity, though.

EDIT nr.2:
This looks like the same bulb, except with the wires already soldered on and the tiny rubber boots in place. Am I correct to think that this would avoid all the delicate soldering and also the need to order the fitting kit? I already have the high temperature tape, shrink wraps and soldering tin...
http://backlightweb.co.uk/index.php?mai ... cts_id=153

[zogthegreat]

Hi tadejr,

If it was me, I would start with replacing the inverter first, then see how it works. Also, it has been my experience that soldering the leads on to the ccfl tubes is a huge PITA. I would recommend getting the pre-assembled tubes.

Is E-bay a possibility where you are? You can get the parts you need fairly cheaply on E-bay. I love to tinker with computers and purchase my hardware there regularly. You could purchase a complete LCD and just drop it in with out risking damage to the screen itself, (as I have done several times!). Although as I said earlier, I would try replacing the inverter first.

zog

[tadejr]

Hi, thank you for your reply.

The thing is, the red hue is supposed to be quite symptomatic of the bulb failing. I think I might need to replace both, but first I'm going to try just the bulb, because the inverters seem to be a bit more expensive, I've seen anything from 20 € up to 50 €.

Soldering the leads is what I'm most concerned about, but I was thinking of practicing a bit on the burnt-out bulb. De-soldering and then re-soldering the wires a couple of times, just to get a feel for it. Overheating the ends and destroying the bulb is the mistake I fear the most.

I've already ordered the bare bulb+kit, because the lead time on the pre-assembled tubes is quite a bit longer. I might order one of those for the second panel if I screw up this one.
E-Bay is a possibility, certainly, but ordering a complete LCD seems like another wager. I already took one with buying the used T60 and it turned out to have an aged panel as well...

I also like the challenge itself. Since I have two panels now, I'm under less pressure to get it right the first time. Maybe I'll be able to fix them both and then I might sell one and recoup some of the money... I might even try to get a motherboard to replace the broken one in the T60 and then I'd have a second machine.

[tadejr]

Here's an update on the situation.

I've received the backlight and the kit and I've managed to replace the backlight... it was very fiddly, but not as bad as I feared. Unfortunately, using my old inverter, the backlight only lights up for a couple of seconds on startup, at normal brightness (as far as I can discern) and then turns off- always at the same point during startup, a little bit before the post screen disappears. Today I received the new inverter and installed it, hoping that would solve the issue. Sadly, the new inverter doesn't seem to work at all, as the backlight doesn't light up at any point.

I'm at my wits end. The replacement inverter is supposed to be new and it was shipped in a sealed anti-static bag. I was careful with the installation. To confirm that the backlight is still working and to make sure I didn't accidentaly burn out a fuse, I installed the old inverter again. It worked just as before (backlight for several seconds, then darkness again).

I sent an e-mail to the store I bought the inverter from, inquiring about my options. It's a spanish store: http://myworld.ebay.co.uk/alcatronics_madrid/

Still, I'd like to know what other issues may present with the aforementioned symptoms (with the old inverter). My soldering work wasn't really top notch, but I'd say if the contacts were to blame, the backlight would be intermittent, possibly responding to pressure applied in the area of the contacts. Instead, it lights up without flickering or odd hues and always turns off at pretty much precisely the same moment.

Thanks, everyone.

[RealBlackStuff]

I wrote a How-to on replacing CCFL: http://forum.thinkpads.com/viewtopic.php?f=31&t=88991
It was for the (easier) 15" IDTech screens.
I refuse to replace CCFLs on any 14.1" or smaller screen, and definitely on ANY LCD from Samsung or Hitachi.

When unsoldering/resoldering the wires on each end of the CCFL, note that the wire used is in an O-shape and slides off/on the metal CCFL-ends after just a little heating up with your soldering iron.
Resolder the O-wire against the glass tube and then carefully cut off the rest of the metal pin.
Then put the silicon cap back on.

You should also check the fuse immediately to the right of the mobo's LCD connector.
If it needs to be replaced, you'll have to take the mobo out of the chassis, and piggy-back solder the new one on top of the old one.

[tadejr]

Thanks Even though my display is a 14.1", I found your how-to quite useful. As I said, my soldering appears to have been successful; I did make a small loop of wire that I slid onto the CCFL ends.

There were two potential problems with the joints - they had a bit of a solder poor area on the side where the wire sticks out, but I tried tugging them slightly and they stayed put. There was another annoyance in that when I put the silicone caps on (I actually got new ones in the CCFL repair kit), they sticked out slightly out of the sides of the metal channel where the bulb resides, because the wire sticked out of my solder bead at a more acute angle than originally. I had to push the wire (along with the silicone cap) inwards. I was worried that could break the connection, but the connection seems fine - like I said, the bulb does light up normally using the old inverter, always turning off at the same moment. I'd imagine if the joints were poor, it would not be so predictable, especially since applying pressure to the area where the joints are doesn't have any effect.

Thank you also for the tip regarding the fuse. I still think it's not the fuse, because then no inverter would work at any time, I imagine. I hope so, anyway... I would feel uncomfortable soldering that tiny SMD fuse :/

[systemBuilder]

So did you get your screen fixed yet? Have you tried going back to the previous inverter (you might do that to see if your soldering skills were up to the task in the new inverter installation)?

It is possible that the new one was soldered incorrectly, or do you think the new one was just defective? Most electronic parts follow a lifecycle called "the bathtub curve" where the chance of failure is very very high in childhood but declining steeply (like one end of a bathtub) and then it reverses and the chance of failure climbs quickly at end-of-life (wearout) period (like the other end of the bathtub. In between there is almost no chance of failure (a really low point like where you lay, in the bathtub). So you probably just got an infant mortality replacement inverter, a stroke of bad luck, but not insurmountable.

[RealBlackStuff]

@systemBuilder:
are you done uttering your incomprehensible nonsense?

[tadejr]

I don't know, actually I found it quite comprehensible. He used colorful metaphors, but the "bathtub" curve of electronic equipment failures is a well-known phenomenon.

Anyway, the situation is as follows; I got a whole display assembly (including the frame and an XGA panel) for a T61 from EBay, along with the replacement motherboard for the faulty T60. I'd hate that machine to just gather dust... whenever I see the colorful IBM logo I just think "man i have got to bring this thing back to life"

Right now, the XGA panel (a Toshiba part, FWIW) is installed in my T61 machine, working well - so the fuses were OK after all. That's a relief.

It still leaves me with the SXGA panel with my kludgy bulb repair job. To summarize- if I use my previous, old inverter, the panel lights up at normal brightness initially and then it turns off at the point where the backlight usually turns off anyway (just after POST). Except that it doesn't light up again after that. With the new inverter, it doesn't light up at any point. The shop I ordered it from swore up and down that it's new and that if I want, I can send it back (at my own expense) and they'd test it. They are willing to send a new one if it turned out to actually be faulty.
Thing is, I'd pay at least 5 euro just for the shipping and I'm really not sure if it's the inverter fault. I'd like to first test it myself somehow.
My rather naive hypothesis is that, assuming that my soldering work was poor, the voltage drop at the bad quality joints might make the actual voltage across the bulb just marginally enough for lighting it up with the old inverter, whereas the new one might have a slightly lower voltage or perhaps some sort of overload protection circuit. I'm not too knowledgeable about electronics yet, because I've just started to really dabble in it, but I can't imagine what else might cause the symptoms I noticed.

I would like to test the new inverter myself somehow, but I'm not sure how to go about it. I'd need an oscilloscope, presumably, but since the bulb isn't lighting up, it means that I probably shouldn't just stick the probes to the terminals... if the bulb were lit, I would basically just be connecting the high impedance oscilloscope voltage measuring circuit in parallel and everything would be fine, but as it is, I would be forcing the inverter to work against the high impedance of the oscilloscope circuit... And since apparently a bad bulb can harm the inverter, this would probably damage it as well. Have I got that right or am I way off the mark?

[RealBlackStuff]

FYI: the CCFL starts up at around 1300-1400 Volts, and once the CCFL is ON, the voltage remains around 600-700 Volts.
I'd be very careful there!
No idea how to test that stuff though.
In the end it might be cheaper to just get another working LCD.

[tadejr]

You are right that this would be the easiest way, but I'm not looking for easy right now, I like tinkering.

Besides, while the voltage @ inverter output is high, the maximum power that the circuit can provide is limited since the fuses on the motherboard are supposed to blow way before anything really dangerous would happen. I'm actually thinking the tiny leads that bring DC voltage to the inverter board are physically incapable of delivering much power before they are destroyed.
That said, obviously I don't want anything to blow either... I'm not doing anything without consulting an electronic engineer. I just thought maybe some of you have done this kind of thing already.

in any case, thanks for the replies. I'll post again if I figure something out. At least I have a working laptop again. And the XGA resolution reminds me of childhood