LCD turns off (can see light image) when AC adapter plugged

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aashtee · #1 Post by **aashtee** » Sat Nov 17, 2007 1:47 pm

Hi,
I have this probelm for last 2 months or so and not sure if it started after some windows update.
When I plug in my AC adapter to charge the battery of my T43 which is just over a year old, The LCD screen flickers and turns off. Actually I can see very faint images.
The battery charges just fine and I can use my laptop only on battery power.

I tried changing power settings to laptop, always on ... etc noting works. I do not see IBM power manager in my programs.

So effectively I cannot work on my laptop until the battery gets charged.

Please HELP!!!!
Regards,
Aashtee

aashtee · #2 Post by **aashtee** » Sat Nov 17, 2007 2:36 pm

I tried installing the power manager also but no use.
Still does not work on AC.

#3 Post by **richk** » Sat Nov 17, 2007 6:08 pm

I have not run across that problem, so I am guessing here. I would guess that the inverter (most likely) or the bulb is failing when it tries to run the lamp at full brightness.

ricerocket · #4 Post by **ricerocket** » Sat Nov 17, 2007 7:05 pm

Haha. I have the exact opposite problem. http://forum.thinkpads.com/viewtopic.php?t=52601

I'm buying an inverter b/c its only $15 or so shipped off eBay.

aashtee · #5 Post by **aashtee** » Sat Nov 17, 2007 8:10 pm

Since you mention it, will the inverter help? how does it work? Can you please elaborate?
I can surely try it out because I m tired of having to charge my laptop between work sessions!!!

#6 Post by **rkawakami** » Sat Nov 17, 2007 9:19 pm

No light being generated inside the LCD panel can have a variety of hardware reasons:

- backlight (aka, CCFL or cold cathode fluorescent lamp)
- inverter
- LCD ribbon cable; which connects the LCD panel and inverter to the...
- motherboard
- lid switch

As you say that the backlight works up until you plug in the AC adapter, I would guess that you have a problem with the motherboard, but let's take a look at each one of the items in the list above.

The lid switch is normally setup to put the laptop into sleep or hibernate modes. This can be verified by looking at the Advanced Power Option settings. If "do nothing" is selected, then that can allow the backlight and display to go off without affecting anything else. As your problem appears only to occur when the AC adapter is plugged in, this is probably not the source of your problem. (Note: this was verified on one of my T41s; a T23 will leave a faint, "ghost-like" image on the screen which means the pixels are working but there's no light. Don't know how the T43 is setup to operate when the lid switch is depressed). Although the switch itself is very inexpensive, it's usually very hard to locate a seller of one and often, even harder to replace since you have to extract the motherboard and/or a separate I/O board to get at the surface-mounted microswitch.

The ribbon cable that connects the signals/voltages from the motherboard to the LCD panel, inverter and status LEDs should also not be affected by being powered from an AC adapter. Fairly inexpensive (~$15-$20 on eBay) but it can be a little difficult to replace (entire lid assembly needs to be taken apart).

The inverter is a small, thin printed circuit board which takes a small DC voltage and converts it to a large AC voltage required by the backlight. richk had a good suggestion earlier that the inverter might have a problem with running at full output. When running on battery, is the brightness (Fn+Home) all of the way up? Easiest thing to replace (remove the LCD bezel is all that is usually required) and cheap; around $10-$20.

The CCFL is really just a small version of the fluorescent tube you have at home or work. It needs a very large amount of current to start up at first but afterwards it doesn't need that much power to keep lit. Costs about $20 for a new tube but it's VERY hard to replace. You basically need to take the LCD panel apart and solder in the new tube (without breaking it).

And finally, the motherboard. There's a whole bunch of stuff on there which can affect many different things. It knows when the AC adapter has been plugged in and it will start up the charging circuits. It can also send a (false) signal to some circuits telling it to shut down something (like power to the inverter). Cost: $$$$$$

So, short answer, try changing the brightness level when the AC adapter is plugged in. If that doesn't do anything, re-seat (remove the connector and re-install) the ribbon cable on the motherboard, re-seat the inverter board at the end of the ribbon cable. If that doesn't work, get yourself another (working) inverter and try that. If that doesn't work then I would suspect something is wrong with your motherboard.

You mentioned earlier about a software (Windows) update. Do you know exactly what that was?

#7 Post by **GomJabbar** » Sat Nov 17, 2007 10:38 pm

If you boot up into the BIOS menu screen or use any bootable CD, is your display still dark with the AC plugged in? If so, then I suspect your motherboard is the culprit. If not, then it is likely a software problem that may require reinstalling Windows.

Brad · #8 Post by **Brad** » Sun Nov 18, 2007 12:08 am

If your T43 is under warranty I think it may be time to give Lenovo a call.

If not under warranty the least expensive repair can be the inverter. After that you could be in for a motherboard.

Which graphics chip does your motherboard have?

Brad

aashtee · #9 Post by **aashtee** » Tue Nov 20, 2007 8:06 pm

Tried out ...
Brightness reduced to min with AC does not work ...
Next I will try Bios to rule out software issues

aashtee · #10 Post by **aashtee** » Tue Nov 20, 2007 8:15 pm

Bios also is not visible on AC

LCD turns off (can see light image) when AC adapter plugged

LCD turns off (can see light image) when AC adapter plugged

Power manager installation did not help

will the inverter help?

Brightness reduced to min with AC does not work

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