No, it is NOT true, although some manufacturers would like you to believe that.
The biggest problem is identifying and purchasing replacement parts. Some of these are proprietary to the manufacturer, who can be pretty choosy about who is allowed to purchase them. Commonly available parts like resistors, capacitors, diodes, transistors, etc. can be replaced if you can identify them or their function. Do what
@(*steve*) suggested: open it up and take a look. There might be something obvious like a burnt resistor, a leaking or bulging electrolytic capacitor, blown fuse, burnt circuit board trace, or any number of other things you can repair without too much knowledge or experience in electronics. If you are stumped, take some close up, well-lighted, pictures of both sides of any circuit boards and upload them here. Don't forget to include manufacturer and model number of whatever you are trying to repair.