It was almost imperceptible at first, but it got worse over time, to the point that the screen would, at random intervals, suddenly dim gradually and then brighten back, for a second or so.
I suspected that the laptop screen was failing. The prospect of having another headless laptop made me anxious. But after a while I noticed that whenever the screen brightness flickered, a battery icon would show up momentarily in the system tray.
So I came up with a theory: it may be some kind of a power supply problem that causes the laptop, for very brief periods of time, to think that it is disconnected from the mains power, causing it to switch to battery power, which, in turn, causes the OS to lower the screen brightness in order to reduce power consumption.
This theory seemed plausible, but with the warranty long-since expired, and without spare parts (power cord, power supply, battery, motherboard, etc.), my only option was to let it go. After all, other than this issue, the laptop seemed to be as functional as it can be.
The flickering, however, made me crazy, so I searched for a way to prevent Windows from automatically darkening the screen when the laptop is switched to battery power.
Well, it's easy, but it ain't obvious:
- disconnect the laptop from the mains power - the screen dims
- use the screen brightness controls to brighten the display back to the same brightness level when the mains power is connected
- reconnect the mains power
A few days ago the laptop switched to battery power and stayed there. I took a little chance and purchased a replacement AC adapter over at eBay. Surprisingly enough, that was it. Happy Happy Joy Joy.