There's an LG flatscreen, 1920x1080, which has been one of my main display screens for some time.
A few days ago, upon sitting down to resume my session, it flashed the display and the power-on light briefly, turned them off again, then about a second later came back on and worked fine. Next time, same thing. Then it started flashing multiple times before settling down. Eventually it got to the point where it was taking long enough to settle down to be a problem in practice.
I had a different monitor do something similar in the past. I fixed that one by re-capping the power supply. That is, by replacing the capacitors, or condensors if you speak East Pondian, in the power supply; lots of flatscreen makers got hit with the subpar dielectric formulation. At a past workplace I was four for four fixing flatscreens by recapping the power supplies. But this monitor has an external wallwart for a power supply rather than a built-in supply.
I opened up the monitor, since it's bound to have, at a bare minimum, a DC-to-DC converter to drive the backlight. None of the caps were visibly bulging. I measured the wall-wart's output. It is marked 19V 1.7A, and, under no load (well, miniscule load, just my Fluke meter), it is reasonably close to 19V. In order to measure results under load, I soldered wires onto the connections from the jack to the board and reassembled the monitor, running those wires out (through the security-anchor lock hole). Hooking the meter to those, I found that the power supply was driving only some 12V or so under load, and with quite a bit of ripple, about 220mV.
I tried putting a smoothing cap, 470μF, on the outside end of those wires. Because of the wires and because it's a large electrolytic with, probably, significant series inductance, it probably wouldn't help with really high-frequency noise, but the original design wouldn't either, with multiple feet of wire between the jack and the wallwart. It reduced the ripple and helped, but didn't cure, the problem.
But then, I had an idea. Since the wallwart sagged so much under load, the monitor clearly could do just fine with about 12V. And I have power supplies all over the place that can drive a good solid 12V into a wide range of loads. So I disconnected the wallwart and hooked one up to the wires I ran out. (I left the smoothing cap connected.)
It works wonderfully. I can only figure that the problem was actually in the wallwart, not the monitor proper, and between the external supply's regulation and the smoothing cap I added, it's now getting good power and isn't unhappy.
I really should pretty this up a bit, using proper connectors instead of the kutcha setup I have now, which has four wires and the smoothing cap connected using a solderless breadboard; if nothing else, I'd rather sub-one-ohm soldered connections instead of the 1-10 ohm friction connections the breadboard provides. I also may cut the wire off the wallwart and use the cable and plug from that, removing the soldered-on wires.
This also points out a common problem with wall-warts (and, usually to a lesser extent, with power-bricks): they are labeled misleadingly. This one is labeled 19V 1.7A. I would initially tend to assume this means it drives 19V and can sustain that into a load that draws 1.7A. It obviously is nothing of the sort. Perhaps it's really more like 19V without load, 1.7A max current before current-limiting foldback kicks in? Or 1.7A into a dead short? I would suspect it of being something like "19V into 1.7A is one of the points on the load/voltage curve", except that that doesn't match well with 19V open-circuit. Back when they were just transformers, diodes, and caps, this was to be expected, but this one is, or at least is marked as, a switcher. Perhaps they couldn't be bothered to add regulatory feedback.
You can, perhaps, see why I put quotes around "fixing" in the title: I haven't actually fixed anything, just worked around the (apparent) actual problem. (Though I suppose in a sense I've fixed something, in that I formerly had a misbehaving flastscreen and I now have a non-misbehaving flatscreen.)