T41/t42p doesn't light backlight

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juhpal · #1 Post by **juhpal** » Sat Sep 27, 2008 10:35 am

Hello,

I got a t42p mainboard (bought it from ebay.de) working in my t41, wohoo!! But: Seller said that this mainboard doesn't lit backlight of the LCD. He thought it was inverter problem. The backlight of my tested LCD won't lit either:( What could be the problem? Should I update bios? External monitor works OK.

juhpal · #2 Post by **juhpal** » Sat Sep 27, 2008 12:03 pm

Update:

OK, the problem seems to be a blown fuse somewhere in the mainboard. The mainboard will charge a battery, but no green indicator. Also no power on indicator, so no power to the screen electronics. Only VGA signal to the screen works, nothing else won't. If someone knows the fuse in the T41/T42/T43(p) mainboard for screen electronics I would save time. Please help

#3 Post by **richk** » Sat Sep 27, 2008 12:35 pm

I have not been able to find a fuse fior this problem, but have fixed it (sometimes) with a reflow of the graphics chip.

juhpal · #4 Post by **juhpal** » Sat Sep 27, 2008 12:54 pm

richk wrote:I have not been able to find a fuse fior this problem, but have fixed it (sometimes) with a reflow of the graphics chip.

Well, if nothing else works, I will make an own small switching regulator for the inverter and take power from input power connector

But well, I will check the fuses first, because the machine from which this mainboard is had an inverter fault. (which has most likely blown the fuse for screen electronics)

juhpal · #5 Post by **juhpal** » Sat Sep 27, 2008 1:47 pm

richk wrote:I have not been able to find a fuse fior this problem, but have fixed it (sometimes) with a reflow of the graphics chip.

OK, got the indicator lights (battery, power on etc.) working by replacung burned fuse F8. So F8 is indicator light fuse! I still have to find the inverter fuse.

sjthinkpader · #6 Post by **sjthinkpader** » Sat Sep 27, 2008 2:23 pm

Here is a fuse map:

T4x/R5x Fuses

juhpal · #7 Post by **juhpal** » Sat Sep 27, 2008 2:30 pm

sjthinkpader wrote:Here is a fuse map:

T4x/R5x Fuses

Thanks! I found the blown fuse F7. I replaced it too and now my T42p/T41 is working flawlessly!!! So F7 is the inverter fuse.

sjthinkpader · #8 Post by **sjthinkpader** » Sat Sep 27, 2008 2:36 pm

I could not find F4, F5 and F14. There is a F marking without number near F2. If you do find these, please let us know.

juhpal · #9 Post by **juhpal** » Sat Sep 27, 2008 2:38 pm

I also found out that in the new board (t42p) the graphics chip Fire GL T2 is glued? with red glue spots to the mainboard. So I hope i will avoid the flexing problem that i had with my T41 mainboard w/R7500. Can somebody confirm that red it is glue? This new board would have had warranty left so i took some risk to repair it myself...

sjthinkpader · #10 Post by **sjthinkpader** » Sat Sep 27, 2008 3:22 pm

The red dots means this board had been repaired or reflowed. They are used to prevent the BGA from collapsing onto the solder balls below.

It will be interesting to know how long it will stay fixed. The board I sent to Hammerhead came back with these red dots.

Preventing the board from getting too hot and reduce the number of cooling/heating cycles (on/off) should help. I seriously doubt flex contribute much to solder balls breaking.

I never held my T41 (Radeon 9000) by the front but turn it on and off at least twice per day and it had a SXGA+ LCD plus a SXGA DVI external monitor connected. It failed two months after the warranty expired.

My colleague likes to hold his T40 with the LCD open to the point front edge of the KB popped out!!! But only turn it on once per day. This machine is still working today.

My empirical data indicate failure will likely occur after 2000 on/off cycles. Temperature delta between hot and cold likely play a big parts too.

raueda1 · #11 Post by **raueda1** » Mon Mar 09, 2009 7:59 pm

juhpal wrote:Thanks! I found the blown fuse F7. I replaced it too and now my T42p/T41 is working flawlessly!!! So F7 is the inverter fuse.

I seem to have exact same problem as OP with T42. LCD display is scarcely visible but external display is fine. I know it's not the display, it works fine on another unit. BUT... I tested all the fuses shown and all test OK (zero ohms on a with DVM). Should i replace F7 anyway or is there something else to try? Very frustrating! Thx.

SlamX · #12 Post by **SlamX** » Sun Apr 05, 2009 9:14 pm

Could be the inverter have you tried a new one?

EinsteinWasRight · #13 Post by **EinsteinWasRight** » Thu Jul 24, 2014 10:58 pm

My ThinkPad T41 display backlight wasn't working in WinXP, but OK on external display. Hinge position made no difference. From forums here and elsewhere I was convinced it was a hardware problem, so I was going to move hard drive to external case, save the RAM, and trash the rest.

Dual boot system. Don't know why, but for the heck of it I restarted into Ubuntu. Before the Ubuntu login screen appeared the T41's main screen lit up! It worked perfectly in Ubuntu, no problems moving the hinge to any angle.

Restarted, backlight off during BIOS splash, boot menu, and WinXP.
Back into Ubuntu backlight working.
Back into WinXP no backlight.

Then in WinXP I used Function-F7 to cycle through all possible int/ext display combinations and then the backlight started working in WinXP! No hardware problem after all!! It has been fine ever since. So basically the ThinkPad got "confused".

I don't know if running Ubuntu helped solve the problem or just revealed that the hardware is fine. I wonder how often this is the explanation for a ThinkPad backlight not working?

[Last time this happened to me with a different model ThinkPad, I tossed it, but maybe it could have been fixed just as easily.]

T41/t42p doesn't light backlight

T41/t42p doesn't light backlight

UPDATE

If nothing else works :)

Update 2

Thanks!

Re: Thanks!

Re: Thanks!

Re: T41/t42p doesn't light backlight

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