No Backlight at Login Screen
Sorry for the long post... This is an annoying problem I've been researching this for three days and trying different things with no success.
I've been running 8.04 on a Dell C640 for about 3 months. Throughout this period, I would have occasional issues with the LCD backlight not working during bootup. In most cases, if I unplugged the power for a second, the display would be fine.
About 7-10 days ago, when I bootup with the power plugged in, the backlight is off unless I do the quick unplug/plugin trick. During the bootup process, I can see everything, and my keyboard brightness keys work fine - I can dim and brighten. After the Ubuntu load status bar completes and disappears, but before the login screen appears, the backlight goes off. Then the login screen comes up but I can barely see it, but it's useless other than to shutdown via Alt-T > D > Alt-D.
Now, if I unplug the laptop during the bootup before the Ubuntu load status bar completes, the backlight will turn on fine, but it is dimmed per the BIOS settings. I can login and work, but the brightness controls are non-functional. The applet moves, but nothing happens, and Fn DnArrow/UpArrow do nothing. Even if I reconnect the power, the display stays in the dimmed mode. If I go into the BIOS and set the "battery" display brightness higher than halfway, the display may not turn on at all during bootup. I've had to reflash the BIOS from a CD to reset the defaults and allow me to boot up again with a working display.
If I connect an external monitor before booting up, all is fine whether on AC power or battery.
I don't know if this is ACPI related, if a recent update did something, or if it could be hardware (LCD inverter). I've tried adding a line /etc/init.d/gdm to set brightness to 100% at the login screen but it had no effect. I've tried disabling power management in the BIOS, and setting acpi=off during bootup.
I have a Dell C640, running Hardy 8.04, 2.6.24-23-generic, GNOME 2.22.3. Video driver is Radeon Mobility M7 LW (ATI Radeon 7500). My BIOS info is
858: Vendor: Dell Computer Corporation
893- Version: A10
1782- Manufacturer: Dell Computer Corporation
1823: Product Name: Latitude C640
1871- Version: Not Specified
2056- Manufacturer: Dell Computer Corporation
2097: Product Name:
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