Alienware M18x R2 missing backlight[edit | edit source]
Troubleshooting Alienware M18x R2 missing backlight
This machine mounts Compal LA-8321P board. This post applies to other machines, with different motherboard, but using similar backlight control.
If we note missing backlight, should check if internal LCD has image at least. If yes, is time to check Q45 area.
See Fig. 1.
Very likely we find +INVPWR_B+ is not present. We must assure no short to ground w/ and w/ LCD connected.
Next will check LCD_BKL_EN signal. If present (3V), then check R423 voltage on both pins. Getting 0V at pin 2 assures Q44 works correctly. 19V there suppose bad Q44; need to change it. If we get 0V at pin 2, but 19V at pin 1 (PWR_SRC_ON), 99% Q45 is bad; replace it. Is still possible (very low chance) to have bad C346 (corroded), or R423 (open).