One possibility is that the power-on speaker protection delay is stuck on. The most common cause of this is a shorted transistor in one of the power amplifier channels. In that case, you will need to replace the speaker driver transistors in that channel. I don't have service information on your particular model; it may use power amplifier modules rather than individual transistors.
The tricky part is identifying the amplifier power and speaker output terminals to test for this problem. To find a shorted output transistor, you need to measure the resistance between the output of each channel and the plus, then the minus power supply connections. There is a relay between the amplifier output and each speaker terminal
on the back; this relay is turned off by the speaker protection circuit, so you can't measure from the speaker terminals. If you have a fried transistor, one of the tests will show a resistance of a fraction of an ohm. A good transistor will have a very high resistance or read open. This will be the case whether you have modular amplifiers or discrete transistors.
If you see a blown fuse, that is a strong indication that you do have a fried transistor. Sometimes the speaker protector circuit shuts down fast enough to save the fuse, but not always.
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