Sony "Protection" mode - STR-DE725

Repair the damaged amplifier.

if you disconnected everything and it still goes into protect, the most likely there is a damaged amp channel that will need to be repaired.

More than likely a blown channel.

Some models of systems will switch to a new source automatically if the source sees a new signal coming on. Try disconnecting the device on your Video 2 to see if this is the case.

I have seen the IC or component(s) in the switching circuits become defective and cause unpredictable or faulty operation. This can also be a fault condition you are seeing.

Yes, it will support a powered subwoofer.

If your existing speakers are from an all-in-one Home Theater in a Box and they have molded connectors you'll have to chop them off to make the ends bare wire and determine which is plus and which is minus on each. Loads of 4 ohms may present a problem at high volume levels.

Take the rated wattage of the sub and other speakers in an HTIB with a HUGE grain of salt. They plays numbers games with th low impedance and the allowable distortion levels to get the results they publish.

For all anyone knows, the speakers and their original electronics may have been designed to operate together to yield adequate performance (like Bose does). Breaking that pairing may give unpredictable results and risk of damage to the speakers or the new receiver.

Do you hear any clicks? If not, the standby transformer or related circuitry is bad. If you hear 1 relay click...the audio output section is most likely the problem. The first click you hear is the main power relay...and should see display.. the second relay click is the protection circuit relay engaging to let audio to your speakers...if the second click is not heard (it should occur in 3 to 5 seconds) there are shorted output transistors or a shorted output IC trying to blow your speakers with 50 to 75 volts dc. The protection circuit monitors the speaker lines for voltage. They should always read milli-volts only...not even 1 volt.Anyway, good luck

Audio Amplifier IC damaged

Go to this site (sony)
http://esupport.sony.com/US/perl/model-documents.pl?mdl=STRDE725

I Have a son STR DE 845 and the speakers make a popping sound when it is in DTS mode what is the problem.

Thanks,
Larry

Here is Sony's support site for that model.