Also see the related document: Troubleshooting and Repair of Consumer Electronic Equipment.
Manufacturer's service literature: Service manuals are available for a great deal of consumer electronics. Once you have exhausted the obvious possibilities, the cost may be well worth it. Depending on the type of equipment, these can range in price from $10-50 or more. Some are more useful than others. However, not all include the schematics so if you are hoping to repair an electronic problem try to check before buying.
Inside cover of the equipment: TVs often have some kind of circuit diagram pasted inside the back cover. In the old days, this was a complete schematic. Now, if one exists at all, it just shows part numbers and location for key components - still very useful. Some TVs - as late as 10 years ago, maybe even now - included a complete schematic with the product information and owner's manual. I have a 1984 Mitsubishi which has this. It is, however, the exception rather than the rule anymore.
Sams' Photofacts (http://www.samswebsite.com/): These have been published for over 45 years (I don't know for how long but I have Sams' for a 1949 portable (3 inch) Pilot TV - about as portable as an office typewriter (if you remember what one of those was like) and are generally the best most consistent source of service info for TVs (nearly every model that has ever been sold), radios, some VCRs and other consumer electronics. For TV servicing, they are indispensable.
There are some Computerfacts but the number of these is very limited. The VCRfacts are also somewhat limited and the newer ones tend to have strictly (obvious) mechanical information.
Even if they don't list your model, they may have a folder for one using the same chassis so search by chassis number as well. Even if this doesn't help, there still may be a folder for models that are similar enough to be of value (though you really have to be in the library to be able to determine this by looking at the circuit diagrams or photos) so check out folders for other model numbers that are close to the one you really want.
You can search this site to determine if they have a folder for your model. Service info (EFacts) for most models manufactured after 1992 is available in electronic form (currently) about $11. These are similar to the print PhotoFacts but may be ordered on-line and will arrive via email within 1 business day. The hard copy versions are also available from major electronics distributors but may be more expensive than the EFacts. However, I don't know how quickly the Photofact is created after a new model is introduced. So, if your set is just out of warranty, it's possible that none is available.
Sams' Photofacts are also often available (for photocopy costs) from your local large public library which may subscribe to the complete series.
One advantage of the Sams' info is that it is compiled in a very consistent format so that once you are familiar with one model TV, it is easy to transfer that knowledge to any other. They provide waveforms at key locations and DC voltage measurements almost everywhere. Additional info such as IC pin to ground and coil resistances are often provided as well. The manufacturer's service manuals are generally not nearly as complete.
Note that I have no connection with Sams Technical Publishing (formerly Howard Sams).
Elsewhere around the world, libraries may also have Sams' or other service information:
(From: Chris Laudan (email@example.com).)
This is true here in UK too, though not Sams photofacts, just schematics issued by manufacturers. Go to the reference library and ask for Video and TV service manuals, most main libraries carry a good selection.
(From: Michael Covington (firstname.lastname@example.org).)
Concerning Sams' Photofacts, here is a bit of history that seems to be very little known:
The name "Sams" is not an acronym, nor is it "Sam." It's the last name of Howard W. Sams, who founded the Howard Sams publishing company (now Sams Technical Publishing). Accordingly, they are "Sams' Photofacts" rather than any of various other spellings that we often see on the net.
And they're a great product. Apparently "Howard W. Sams & Co., Indianapolis, Indiana" is a sufficient address to reach them. So is 1-800-GAT-SAMS.