I have a TLA7012 logic analyser that I use on occasion. It hadn't been powered up in a long while and when I wanted to use it again the backlight was very dim, to the point of the screen being barely visible at all. My fist thought was that either the backlight or the inverter were bad, but it turned out to be something completely different that I hadn't expected.
The BIOS has a setting that determines how the backlight is controlled. It can be set to "I2C" or "PWM". The default is "I2C" but the TLA actually needs it to be "PWM". When the CMOS battery on the motherboard dies, the setting reverts to "I2C" and you end up with a dim screen. Replacing the battery and selecting "PWM" in the BIOS fixed the issue.
I found this surprising, so I post it here in case anyone else runs into this issue.