Dark Screen - Anything OTHER than backlight?

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RWDPLZ · #1 Post by **RWDPLZ** » Mon Aug 20, 2007 2:28 pm

I just recieved in the mail a new screen for my A31p. What showed up was actually a screen for an A30p, but according to the HMM they use the same parts. No big deal.

SO I install the screen, boot it up, and the screen is really dark. I can just barely make out the IBM logo. If I shine a flashlight on the screen I can just barely see things better, depending where I point the flashlight.

I swapped out the inverter with the one from my old screen (which ALSO had a bad backlight), and had the same result.

Could this problem be anything other than a bad backlight? The eBay seller claimed it was tested and in good working condition, but he also called it an A31p screen. I'm quite [censored] right now.

#2 Post by **carbon_unit** » Mon Aug 20, 2007 2:42 pm

Have you connected an external monitor up to it? That will tell you if the video chipset is bad. It could also be the ribbon cable from the motherboard to the display panel or the actual CCFL lamp itself is bad.

RWDPLZ · #3 Post by **RWDPLZ** » Mon Aug 20, 2007 3:16 pm

Works fine when connected to an external monitor, before and after installing the screen. Before I got the screen I had it hooked up to an external monitor and was using the base unit as a keyboard, it felt like using an old Apple IIc

The screen came as a whole self-contained unit, with it's own new inverter and ribbon cable, which are oing the same thing as the original screen (extremely dark). Adjusting the brightness doesn't do anything either. That's why I believe it's the backlight.

It was eBay item number 130141977980 for anyone that wants to see the auction.

#4 Post by **tomh009** » Mon Aug 20, 2007 3:28 pm

Did your A31p's backlight originally work, or did you buy it with a broken backlight? I wonder if there might be a bad connection somewhere, as it's a bit suspicious that you have two screens with bad backlight symptons.

RWDPLZ · #5 Post by **RWDPLZ** » Mon Aug 20, 2007 3:46 pm

I bought the computer with a bad backlight. I was hoping a new screen would have a working backlight and fix the problem. The seller never provided any proof the screen infact worked before I got it though, and I don't have another A31p to test it in, unless you can put a UXGA screen on an XGA Thinkpad (which I'm 99% sure you can't).

#6 Post by **carbon_unit** » Mon Aug 20, 2007 3:49 pm

As long as you have the ribbon cable I think you can.

RWDPLZ · #7 Post by **RWDPLZ** » Mon Aug 20, 2007 4:13 pm

I think you can't ecause of this thread:

http://forum.thinkpads.com/viewtopic.php?t=21740

With my old screen, I tried taking it apart and replacing the backlight, as in this link:

http://sourcepower.co.nz/A31/A31Backlig ... ement.html

Unfortunately while I was taking it apart, I bent one of the films, threw out the whole mess in frustration, and decided to get another screen.

Since the backlight is powered by the 2-pin connector off the inverter, can I connect a voltmeter accross the two terminals and see if the backlight is getting any power? How many volts should it read? Similarly, can I plug in my extra backlight bulb to the inverter and see if it lights up?

#8 Post by **carbon_unit** » Mon Aug 20, 2007 4:28 pm

RWDPLZ wrote:I think you can't ecause of this thread:

http://forum.thinkpads.com/viewtopic.php?t=21740

You are right. I learn something new every day and today it is this.

RWDPLZ wrote:With my old screen, I tried taking it apart and replacing the backlight, as in this link:

http://sourcepower.co.nz/A31/A31Backlig ... ement.html

Unfortunately while I was taking it apart, I bent one of the films, threw out the whole mess in frustration, and decided to get another screen.

I've changed my last backlight bulb also. What a major PITA.

RWDPLZ wrote:Since the backlight is powered by the 2-pin connector off the inverter, can I connect a voltmeter accross the two terminals and see if the backlight is getting any power? How many volts should it read?

I don't think I would attempt this. The voltage is high enough to jump between the two pins if you don't use an insulated connector.

RWDPLZ wrote:Similarly, can I plug in my extra backlight bulb to the inverter and see if it lights up?

That should be OK.

#9 Post by **rkawakami** » Mon Aug 20, 2007 4:54 pm

RWDPLZ wrote:Since the backlight is powered by the 2-pin connector off the inverter, can I connect a voltmeter accross the two terminals and see if the backlight is getting any power?

No! I tried that and heard a pop, saw a flash and ended up with a burnt plastic clip.

Output voltage from the inverter can be in the range of many hundreds of volts to over a thousand. The backlight is a fluorescent lamp and as such requires a large voltage (and current, I believe) to start up. From my research it appears that you can't simply use a voltmeter.

http://forum.thinkpads.com/viewtopic.php?t=34876
http://forum.thinkpads.com/viewtopic.php?t=34561

edit: I just remembered/thought of something from my days with playing around broken TVs. A trick back then was to hold a neon bulb (disconnected and insulated from yourself) around the high voltage section. If it lit up, the power supply was working. Not sure exactly how much voltage would be required but I'll try this with an inverter board. Certainly would be useful to determine if an inverter is working or not.

pjm99au · #10 Post by **pjm99au** » Wed Aug 22, 2007 7:39 am

I don't know the a31 but if it has one I'd also try playing with levering up with a small flat bladed screw driver the small micro-switch which turns off the screen when the lid is closed. This fixed a similar problem of a dark screen on my r40

#11 Post by **rkawakami** » Sun Sep 02, 2007 6:48 pm

Earlier, I wrote:A trick back then was to hold a neon bulb (disconnected and insulated from yourself) around the high voltage section. If it lit up, the power supply was working.

Confirmed. See this thread:

http://forum.thinkpads.com/viewtopic.php?t=48910

Dark Screen - Anything OTHER than backlight?

Dark Screen - Anything OTHER than backlight?

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