A common problem with CRT displays is a dim picture. This can happen for several different reasons, and this page will go over them.
You've checked the brightness controls, right? Some CRTs have a hardware control (such as a stand-alone monitor), while many All-In-One computers may need to be adjusted in software.
If you have adjusted the brightness already, and still have a dim picture, you may also want to check the CRT Analog Board, as many boards have a a seperate control on the board itself that can be adjusted for an improved picture.
Another potential cause of a dim CRT picture is (you guessed it), faulty capacitors. Bad caps can cause CRT quality and picture issues, although they are more likely to do with the shape of the picture, or the ability to display a proper picture itself, not the brightness.
Replacing the capacitors on the CRT's analog board is a good place to start troubleshooting a dim picture, but it isn't that likely to be the cause.
The most likely cause of a dim picture on a CRT display is the CRT itself growing weak. High-hour CRTs can often have lower "emmisions" than less-used tubes, and lower emmisions brings a dimmer picture.
A good thing to check first here is to look for burn in on the tube. If you can see any burn-in on the display, it's likely seen a lot of use.
Unfortunately, not much can be done about a worn-out tube. Devices exist that can "rejuvinate" the tube, potentially restoring lost emmisions, but these tools are rare, expensive, and rarely work. While it is possible to use them to get more life out of a worn-out tube, you are more likely to damage it further.
Failed rejuvinations can cause:
Due to these concerns, it's only really worth trying this method on tubes that cannot be used as-is. If a rejuvination works, it may only brighten up temporarily as well.
Video showing a successful rejuvination of a Macintosh Plus CRTIndex < Important Issues < Dim CRT Picture