Hi I have a Sony STR-KM2 amplifier and it keeps saying USB fail and switches off. any suggestions on how to fix it?

SOURCE: Sound turns off for Sony STR-DE875 amp

If you do not here a click as soon as the power is turned on, (note you must be in a very quite environment no noise absolutely to hear this) then the amplifier has blown output transistors which are pushing DC current to the speakers.

SOURCE: Can you hepwith my sony LCD Problem?

It could only need some soldering of the display itself. If you want to try it your self.
remove the top cover (you may need to remove the front panel also)

1. inspect the twenty or so pins of the fl display tube especially the end ones (resolder if bad).
2. if they all look good check for DC voltage on the end pins (20 to 30 volts)

The Knight

• 76851 Answers
• Posted on Aug 12, 2015

SOURCE: What's your question?Sony STR-KM2 no sound the relay click two times still no sound please help

Short circuit protection section energizes. The should be any short circuit, either outside the set or inside. Disconnect all the speaker connections and check. If no short circuit symptom; after disconnecting the speakers, try connect it one by one before each switch ON, and make sure about which connection shows the short circuited speaker. If even after all the external connections are removed, and still the short circuit symptom occurs, the fault is with its internal power amplifier section circuit. Contact any service technician in this case, to rectify the problem. If you wish to get some details; check the site linked here. Pull up older posts. Surf the site with patience. http://electronicshelponline.blogspot.com/