Backlight or Inverter?

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Stargate199 · #1 Post by **Stargate199** » Tue Feb 20, 2007 12:01 pm

Okay, I might be in trouble if I can't find a replacement screen soon. This morning when I fired up my T21, the backlight did not come on. I know that the LCD is working because I see the image on the LCD. Now I know that my backlight is going bad (pinkish redish tint of startup), but after 15 min of playing around with it, the backlight came on! Funny enough, it came on when the Win XP boot screen came up. I have had trouble getting the backlight to come on, but I thought it was the inverter board because if I put pressure when it was on startup, the backlight would come on. Now I'm not sure. It seemed like today that the backlight was not energizing. Anyone have a guess what I need to replace (besides replacing the entire lid assembly as a whole).

#2 Post by **rkawakami** » Tue Feb 20, 2007 1:39 pm

First thing to check is the lid closure switch in front of the right hinge cover. With the laptop off, slightly push down on it a couple of times real fast, then turn the system on. If the switch is dirty/stuck, that can cause the backlight to not turn on.

If that doesn't get it to work, find/buy another inverter and see if that helps. If that doesn't work, then try another panel.

That said, I still have a 600E that refuses to turn the backlight on for at least 5 minutes. That's after replacing the Sub Card (where the lid switch is), the inverter and finally the entire LCD panel. I believe the problem to be on the motherboard. It has always turned on after several minutes.

Msmax · #3 Post by **Msmax** » Tue Feb 20, 2007 3:54 pm

@Ray,
Will there be a dark image on the LCD if the cover switch is damaged/not working? I do not hink so, but have not tried it yet. If the lid is closed then not only the backlight is switched off but also the video signal to the LCD is switched off.
So my guess is that with a dark image on the LCD the inverter, backlight tube or the LCD cable can be the cause of this problem.
Please let me know your thoughts about this. Would be great if you could test this on a machine, just to be sure. If not, I will test it on the next notebook I disassemble.

@Stargate199,
Have had about 4 IBM T2x machines with same problems as described by you. Everytime the problem was traced back to the LCD cable.
You can try to do a LCD cable continuity test if you have a multimeter available from the connector which fits the mainboard to the connector on the inverter board. In my case every time 1 track was broken: the one to switch on the backlight.

Msmax

#4 Post by **rkawakami** » Tue Feb 20, 2007 4:14 pm

Msmax wrote:@Ray,
Will there be a dark image on the LCD if the cover switch is damaged/not working? I do not hink so, but have not tried it yet. If the lid is closed then not only the backlight is switched off but also the video signal to the LCD is switched off.

Ah, yes, I believe you are correct and I'm wrong on that point. The lid switch should kill the video signal as well as the backlight. I read past the description that Stargate199 had about the image on the screen. And yes, a ribbon cable could be a problem as well as the inverter.

dogma420 · #5 Post by **dogma420** » Wed Feb 21, 2007 10:44 am

use a knife to jam 'open' the lid is closed button...this is a bad keyboard bezel.

dogma420 · #6 Post by **dogma420** » Wed Feb 21, 2007 10:46 am

lid switch DOES NOT kill video signal, only the backlight...if it killed video signal then it would not show up on ext mon either

Msmax · #7 Post by **Msmax** » Wed Feb 21, 2007 11:25 am

How come one can select to display:
- LCD only
- External screen Only
- Both

Because analogue switchers are used to enable/disable output signals. The wires to the LCD are not directly connected to the wires of the VGA output connector.

Msmax

danage · #8 Post by **danage** » Wed Feb 21, 2007 12:21 pm

just try the switch on a working t23 and the discussion will be obsolete. i don't have one unfortunately.

#9 Post by **rkawakami** » Wed Feb 21, 2007 1:48 pm

The lid switch will kill ONLY the backlight and leave the video signals going to the LCD, IF the power settings under Windows says "do nothing" when the lid is closed. It may also be controlled from a BIOS setting. I'll have to get one of my other systems and see.

This was just tested on the T23 I'm using. I normally set the lid switch to go into standby so that's why it killed both the backlight and video signal to the LCD yesterday.

Msmax · #10 Post by **Msmax** » Thu Feb 22, 2007 3:55 pm

@Ray,
Confirmed, same behavour on my T21.

Msmax

Stargate199 · #11 Post by **Stargate199** » Thu Feb 22, 2007 4:31 pm

Thanks all. From what I understand, it could also be the video cable, or the lid close switch. I will open my T21 to look at things, but most of my tests seem to lead to the inverter board.

#12 Post by **tomh009** » Thu Feb 22, 2007 6:50 pm

For sure, the pink hue points to the inverter board, so that's definitely going. It's possible (though IMHO not likely) that something else also has a problem, but since the inverter is going, I would replace that first and then see whether there is another issue still present.

Stargate199 · #13 Post by **Stargate199** » Thu Feb 22, 2007 7:38 pm

Actually, pink hues are caused by an aged backlight that needs to be replaced, but my guess is that may get better with a new inverter board. I would replace the CCFL (backlight) tube myself, but I lake the skills needed to do it successfully.

Stargate199 · #14 Post by **Stargate199** » Thu Feb 22, 2007 7:42 pm

Okay, I took everything apart, reset the video cable and I still have the problem. I am absolutely sure its the inverter now. Alphakilo470 may (and I stress MAY) have a replacement inverter, but I will need to see. Meanwhile, I will hunt down the parts I need else where. Maybe one of my friends has a broken T2x computer I can sacrifice

#15 Post by **tomh009** » Thu Feb 22, 2007 8:13 pm

Not expensive at all on eBay. Here is one example:
http://cgi.ebay.com/ws/eBayISAPI.dll?Vi ... 0081906211

Msmax · #16 Post by **Msmax** » Fri Feb 23, 2007 6:00 am

@Stargate199,

Why don't you do a continuity check wit a multimeter?
Then you know for sure if the LCD cable has any broken tracks or not and this test costs nothing!

Put the LCD cable on a table with the mainboard & inverter connector towards your self and facing up.

There should be a short between:
- Inverter connector 5th pin from left bottom row &
- Mainboard connector 8th pin from left bottom row

If this is open just replace the LCD cable.

Msmax

Stargate199 · #17 Post by **Stargate199** » Fri Feb 23, 2007 9:31 am

I don't have a multimeter, but I know the inverter is the problem because I took it out and inspected it. It looks like there possibly may be some burn marks on circuit board (most likely due to a big static shock a received when I touched the the computer a few weeks ago. It was a big shock by the way). Alphakilo470 (who lives down the road from me) has a few spare boards that may work. I'm going over there later today to look at them and see if they may be compatible.

Stargate199 · #18 Post by **Stargate199** » Sat Feb 24, 2007 9:00 pm

None of Alphakilo470s inverters work. I did track down some T21 parts elsewhere. Hopefully they will come soon.

Backlight or Inverter?

Backlight or Inverter?

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