Lenovo T43 Laptop Display dimming

So how can I tell if it is the display, the backlight, or the inverter?

And could someone give me an idea what's involved in replacing each?

Reply to
spamtrap1888
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Clean the screen. Fire up the laptop and get it to boot. Darken the room. Use a flashlight at an angle to see if you can detect any text on the screen. For Windoze, you should see the Windoze logo as it boots. If you do see an image, your LCD panel is probably fine, and you are having a problem with the LCD inverter or the CCFL lamps in the panel.

It's also a good idea to plug an external monitor into the VGA port to see if the video card is working.

Determining if it's the inverter or the CCFL lamp is a bit tricky. If you get a pink colored dim background, it's probably the CCFL lamps. These are a major project to replace. You'll find instructions on web sites selling LCD panels and CCFL lamps.

The way to be sure is to open the display section and attach a test CCFL lamp to the inverter.

The LCD inverter is in the display section of the laptop. You only need to go to Step #9. The hard part is splitting the LCD frame. Don't use a metal screwdriver to pry open the display.

I usually buy two to avoid surprises. Note that there are different part numbers for different display types. You'll probably have to get the number off your inverter to be sure which is the correct number.

Bug me if stuck.

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Jeff Liebermann     jeffl@cruzio.com
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Jeff Liebermann

What do you mean by dimming? Dim? Dark? off?

Another way to check the inverter is to waive an oscilloscope probe around the area of the inverter. If it's running, you can often see the radiation from it on the scope. That won't prove the inverter board is good, but might lead you to check the lamp before buying an inverter. Don't go probing the inverter circuit unless you know what you're doing. There's voltages there that the scope won't like at all. You might find yourself with a dead laptop and a dead scope.

Most people don't have 'em, but an ultrasonic leak detector translates ultrasonics down to the audible range. You can easily hear the inverter transformer "singing" and hear it change as you adjust the brightness setting.

I'm interested in hearing how to check CCFL lamps. In the old days, you could plug on just about any inverter and see if it lights. Today, the proliferation of connectors and inverter topologies makes this harder.

I bought a fluorescent lamp checker at a garage sale. It's basically a transmitter. You waive the antenna around the lamp and see if it lights. Works great on household fluorescents. I've been afraid to try it on a laptop for fear that it'd blow up the display drivers.

I don't have that model, but I did have a thinkpad with a bad fuse. Was located near the display connector and well disguised. Didn't look like a SMT fuse at all. Was open and extinguished the backlight.

Reply to
mike

I suspect it is my CCFL lamp, because I still have an image, and it has a rosy glow. I haven't found a good page explaining how to replace the CCFL, though. Are they fairly generic, or do I need to make sure I have an OEM replacement? And can you suggest a good set of replacement instructions?

The inside-my-laptop site seems to recommend replacing the whole display even if just the CCFL is faulty. Is replacing the CCFL that much of a nightmare? My display is actually pretty good, so if I could just replace the CCFL, I would, rather than take a chance of getting a crap LCD.

Thanks so much for your help.

Reply to
spamtrap1888

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Dim. Going but not gone.

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Backlight is still working somewhat. A lot of good tips, thanks.

Reply to
spamtrap1888

I suspect it is my CCFL lamp, because I still have an image, and it has a rosy glow. I haven't found a good page explaining how to replace the CCFL, though. Are they fairly generic, or do I need to make sure I have an OEM replacement? And can you suggest a good set of replacement instructions?

The inside-my-laptop site seems to recommend replacing the whole display even if just the CCFL is faulty. Is replacing the CCFL that much of a nightmare? My display is actually pretty good, so if I could just replace the CCFL, I would, rather than take a chance of getting a crap LCD.

Thanks so much for your help.

+++++

Felt-tip pen marking junctions of materials and photographs while taking apart is advisable. Don't pull on anything that looks as though it should be free, there maybe something at the other end unseen , that is locking it in place. Without all the framework stuff, the tubes are about as fragile as spaghetti and not much thicker.

Reply to
N_Cook

Here's another article on the problem:

When the CCFL bulbs crap out, the display initially becomes pink colored. As more air leaks in, the CCFL lamp becomes dimmer and dimmer until it finally quits altogether. Some inverters have protection circuits to detect CCFL faults and will turn off the display after a few seconds. I forgot what the thinkpad inverters do. Note that this is for CCFL backlighting, not LED backlighting.

Good idea.

Bah. I use two 10:1 probes setup for differential input. My probes will handle 1000VDC so there's not going to be a problem with the typical 500-700V peak output from the inverter. However, if you forget and set the probe to 1:1, there's going to be an expensive problem in the scope.

Great idea. I have an HP 4917A and never thought to use it to check the inverter. Thanks.

I have an inverter used by gamers to light up the inside of their tower cases glued to a board. I've ripped off connectors from dead LCD inverters and built a connector octopus. I've only found 4 different HV connectors so it's not an ugly mess yet.

Don't do it. Chances are good that you're going to apply HV to some place that won't appreciate the voltage. Incidentally, I have a customer that keeps blowing up monitors, mice and keyboards. It's obvious that it's his "negative ion generator" that's causing the problem, but he insists on using it near the computah.

I saw that on a Thinkpad T22 or T23. If you short something in the external LCD connector, it blows the fuse, which also kills the LCD display. The clue is that BOTH the internal LCD and external video are dead. I found a rather vague article on the problem:

Finding the fuse was easy. There was an F(something) reference designator silkscreened nearby.

Incidentally, I have several USB microscopes that are quite handy for looking at SMT components that my rapidly fading eyesight can't see.

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Jeff Liebermann     jeffl@cruzio.com
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Jeff Liebermann

Don't assume it's the CCFL quite yet. It's best to verify that the inverter is doing its job before attacking the LCD panel. That means hanging another CCFL lamp across the inverter output to see if it lights up, and applying voltage from an external LCD inverter to see if the CCFL lamp is any good. I would not try to replace the CCFL lamp until you've clearly identified it as the problem.

Also, as a contingency, I would buy a replacement LCD inverter on eBay simply because they're cheap and I hate waiting for parts to arrive.

I just wrecked a Toshiba panel so I may not be the best person to ask. These are the link I bookmarked for the exercise:

It is NOT easy and you will probably wreck a few panels as part of the learning process. If you can find a dead LCD monitor, it might be useful to tear the panel apart for practice.

You can find panels on eBay, but they's not cheap:

If you look at the first link above, you'll probably see the burned spot on the CCFL terminal and rubber boot. This is where the HV has arced over to the frame. It's also where the CCFL lamp terminal got hot, and slightly charred the rubber boot. I've had to use high voltage RTV (from my TV repair kit) to make sure that the insulation is intact on reassembly.

The big danger in replacing the CCFL is in peeling or even touching the row/column connections going to the LCD panel itself. Break the connection and the panel is dead. I can sometimes use my hot air SMT desoldering station to repair the damage, but my batting average is lousy.

What's your time worth? About $100 will get you a new display with CCFL lamp. My shop time is $75/hr. I can do the CCFL job (including checking out the laptop, cleaning out the dust, etc) in about 2 hrs for a total of about $170. Or, I can replace the panel in 1 hr, for a total of $175. Given the high chances of failure with replacing the CCFL lamp, I would suggest a panel replacement.

It really depends on which LCD panel you have.

The T43 comes in 1024x768 or 1400x1050 in 14" and 15" panels. If you have a 1400x1050 15" display, it might be rather expensive to replace.

If you have the time, and are willing to take the chance, I would try the CCFL replacement. The only catch is that the lamps are about $15-$25/ea including shipping, which makes this a potentially expensive learning experience.

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Jeff Liebermann     jeffl@cruzio.com
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Jeff Liebermann

You've got better probes than most people. Probes are significantly derated at higher frequencies. What's the peak voltage out of the inverter when the lamp is open? Bottom line is that most people asking the question asked here would be better off not probing the output of the inverter.

Got a recommendation for a cheap one of those? I got my hands on one once with a killer zoom, but didn't think I'd use it. Wish I'd bought it. I do have a dental camera with fiber optic light source. Looks like a colonoscopy machine. Gets real close, but takes up way to much space to justify infrequent use.

The ideal solution would be a high resolution camera with autofocus and zoom. Need to get it far enough away to make room for the soldering iron under it. I still haven't mastered the coordination needed to look one direction at a display and solder in another direction.

Reply to
mike

You shoulda led with that statement. That's common among IBM laptops.

Replacing a lamp is a crap shoot. I've done some that had removable panels that gave access to the lamp. Others have it buried DEEP in the frame and you have to completely disassemble the display. Be very careful when you unfold the boards with the display drivers. It's not difficult to turn a dim display into one full of bright lines. Don't mix up the order or direction of all those plastic sheets that fall out.

Like most things, it's a LOT easier the second time you do it.

Reply to
mike

Amazing technology in their own right those sheets of plastic - I've never seen a laptop with a noticeably dim centre of the display or farthest edge, if only one light tube.

Reply to
N_Cook

I once replaced both the inverter and the tube on a Thinkpad, only to discover that the actual problem was a break in one of the conductors of the ribbon cable joining them.

Sylvia.

Reply to
Sylvia Else

I don't know, but I can measure one after I'm back from my mini-vacation. I don't like running the inverters without a load as I'm afraid the xformer will arc over. So, I've never bothered to measure it. Also, some inverters will shut down if they see an open or a shorted load.

My probes are nothing special. I bought them on eBay from some random Chinese source. I got tired of constantly fixing my collection of HP and Tek probes. So, I bought 10 new probes and am slowly blowing them up as I blunder forward. By using two of these probes with differential inputs to the scope, I essentially double the maximum voltage rating of the probes.

What I really should use is a 100:1 probe that can handle 1200VDC:

Maybe. However, I figured that anyone that owns an oscilloscope should know something about how to use it and about its limitations.

Same problems. I bought several different styles on eBay for about $20/ea. Something like this one:

All are rather crudely built, fat, etc. No adjustable illumination. Very crude mounting hardware. The software universally sucks, but fortunately there are substitutes. A major problem was that the required drivers all interfere with each other, with my microscope camera, and with my other USB video cameras. I don't know what to recommend because nothing works perfectly.

The original plan was to strap the camera on the back of my hand to aid in soldering. I'm getting old and my eyes are deteriorating. I have trouble seeing SMT parts and thought the camera will help. It does, but due to the lack of depth of field, the ability to keep the camera in focus is limited. I've switched to surgeons eyeglasses, which are much better.

I just put a layer of cellulose wrap over the camera lens to keep the flux fumes from trashing the lens. Doesn't affect the image very much, but does keep the lens clear. What I would really like is a pseudo color far-IR camera, so I can see how hot things are getting when I use my hot air SMT desoldering gun.

Yeah, that was another problem. I did OK, but was still somewhat clumsy. The surgeons glasses were much easier.

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Jeff Liebermann     jeffl@cruzio.com
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Jeff Liebermann

It is difficult to tell if the CFL tubes or the power supply is bad unless = you have the proper test equipment to determine this. Generally speaking, a= fter the CFL tubes go weak, the power supply also has a lot of wear on it. = When I used to change the CFL tubes I also changed the power supply at the = same time. This gives better reliability.

Reply to
Jerry G.

It is difficult to tell if the CFL tubes or the power supply is bad unless you have the proper test equipment to determine this. Generally speaking, after the CFL tubes go weak, the power supply also has a lot of wear on it. When I used to change the CFL tubes I also changed the power supply at the same time. This gives better reliability.

++++

Can something weaken in the inverter section , assuming a perfectly good tube ? Or is it just increase in leakage through disc ceramics, wiring or Tx winding insulation.

Reply to
N_Cook

Was the symptom no video at all?

Reply to
spamtrap1888

s you have the proper test equipment to determine this. Generally speaking,= after the CFL tubes go weak, the power supply also has a lot of wear on it= . When I used to change the CFL tubes I also changed the power supply at th= e same time. This gives better reliability.

Jeff L: How necessary is this?

Reply to
spamtrap1888

Jeff Liebermann wrote in news: snipped-for-privacy@4ax.com:

one thing; there's usually a film cap between the two CFL filaments,that with the tube OFF,has a relatively low reactance compared to the unlit tube,and allows the filaments to conduct the voltage and heat up,and after the tube strikes it's arc,the arc shorts around the cap and the filaments turn off. If that cap shorts,the tube will never strike an arc,and the filaments stay lit.

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Jim Yanik
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Jim Yanik

Nope. There are no hot filaments on CCFL tubes. That's why they're called "cold cathode".

I've taken apart many LCD panels and have never seen a capacitor at the CCFL lamp terminals. There's the stiff wire coming out of the glass tube, a flexible wire soldered to it, and a rubber insulating cover. No capacitor. Something like this:

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Jeff Liebermann     jeffl@cruzio.com
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Reply to
Jeff Liebermann

Probably a good idea especially if the LCD inverter is cheap. In the T43, the LCD inverters on eBay are quite cheap at $4 to $6/ea. If you recall, I suggested that you purchase two:

It's true that trying to drive a failing CCFL tube is going to cause problems with the LCD inverter. What happens is that as the tube becomes gassy, it ceases to conduct, which causes the LCD inverter to drive an open circuit. That raises the voltage at the transfomer output. Eventually, the insulation on the transformer breaks down and produces tiny arcs. This does take a while, but most users will try to use the laptop until the display completely quits. Eventually, the transformer will short, but in the mean time, the xformer will have holes in the insulation. These could arc over later for other reasons (e.g. moisture)[1]. There's no guarantee that whatever you buy on eBay is any better than what you're replacing, but the odds are in your favor. That's also why I suggested buying a spare inverter.

Hmmmm... ebay lamp prices vary from $4 to $18.

[1] I've only done 4 autopsies on LCD inverters to see what has failed. In 3 of the 4, the xformer had a shorted turn. I'm not sure if this is a common characteristic as all 4 came out of identical HP something laptops. I never could determine the cause of failure on the 4th inverter.
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Jeff Liebermann     jeffl@cruzio.com
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Jeff Liebermann

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