Recently I bought an old ThinkPad R32 on Tradera, the Swedish equivalent of EBay. The plan is to use this laptop as the basis of a DIY tablet-PC project.
Anyway, I got the laptop cheap because the LCD panel was broken. The LCD displayed an image but it was very dark, a classic backlight problem. After a bit of googling around I found out that either the CCFL (Cold cathode fluorescent lamp) or the LCD inverter could be the cause of the problem. The CCFL is basically a lamp which illuminates the LCD pixels from the backside while the inverter is a circuit board which supplies the CCFL with the correct voltage.
Replacing a CCFL seems very complicated while replacing the LCD inverter is trivial, at least on this particular ThinkPad model. According to Google the most common cause of backlight problems is the inverter. To confirm that this was the case I ripped the LCD panel out of my old ThinkPad A20m and connected it to the inverter in the R32. I figured that if the R32’s CCFL was broken the A20m’s LCD panel would light up when I plugged it in. It didn’t light up but I did see the same very dark Thinkpad logo during the BIOS initalization so I concluded that the inverter was the problem. After a quick search on EBay I found a new inverter for $30 including shipping to Sweden.
When the inverter arrived after about a week I followed the instructions over at Laptop Repair to replace the old one. Unfortunately, nothing happened when I turned on the laptop. What Laptop Repair fails to mention is that, at least with ThinkPads, you may have to run a program which updates an EEPROM chip on the inverter after it has been connected. This EEPROM stores the id (manufacturer and size) of the panel connected to it. If the wrong id is set or no id is set at all the panel will stay black.
It took me a while to find this information in the ThinkPad R32 Series Hardware Maintenance Manual:
System board/LCD/Inverter replacement notice
Restoring the LCD panel ID
The EEPROM on the inverter stores its supported LCD type ID code. If you replace a LCD with one of a different brand or use a new inverter, the ID information in the inverter EEPROM should be updated.
Follow the steps blew to set the LCD panel ID:
1. Install the ThinkPad Maintenance Diskette and restart
2. When the IBM logo is displayed, press the ′′ESC′′ key
few times until BIOS copyright and diagnostics screen
3. Select 1. LCD Panel ID Utility from the main menu.
4. Follow the instruction on screen to read current or to
set new LCD Panel ID code.
5. Restart computer : the new LCD should work normally.
I quickly found the ThinkPad Maintenance Diskette. Then I spent hours and hours trying to get it to boot from a USB memory stick. According to the forums I’ve read this disk MUST be booted from a floppy drive (it can be a USB floppy drive). The forum posts say that making a bootable CD out of it will not let you write to the EEPROM. Since I don’t have a USB floppy drive at my disposal I tried for days to get the floppy image onto a memory stick and fool the ThinkPad into believing that the memory stick was a floppy disk. It’s supposed to be possible. I finally gave up and bought a USB floppy drive on Tradera.
Now I was finally able to boot the damn disk using the floppy drive but it didn’t seem to be the right disk. No such thing as “1. LCD Panel ID Utility” turned up in the menu. After a bit of more googling I discovered that the maintenance manual was incorrect. I should have used the so called ThinkPad CE Utility Diskette instead. Thank you IBM!
After a couple of hours I managed to find the correct version of the CE Utility Diskette for the R32 ThinkPad model (this link was of great help). First I ran the LCD Panel Utility with the old inverter in place to get the correct LCD Panel ID. Then I replaced the inverter and ran the utility again to set the correct LCD Panel ID. And now, finally, the backlight works great!