Denon Home Audio Video Receiver AVR391. This is an entry level home theater receiver.

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Why is a red light flashing?

When the sound is too loud the receiver shuts off. Now a red light is flashing around the power button and the receiver will not come on. I have already tried to reset it.

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Here is the User Guide explanations for a red light flashing on your receiver.

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Hopefully is it of some help.

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I know that this is a late posting, but some explanation is required.

The red blinking in general is an indication of “protect” mode. This is a case where a problem has been detected and the unit shuts down to prevent further damage to either the receiver or the speakers. As indicated in the posting above, this can happen for a several reasons.

1) Heat - When the receiver works too hard and generated too much heat, it will shutdown the speakers until the temp reduces to a safe level. Once cooled, the receiver will function again as expected. Excessive volume for an extended period of time can trigger this. This is what was reported in the original question.

2) Failure of the Amp section - In this case, the unit will show the protection stage immediately upon turning on. This is the shorter interval flashing. In most cases, the output transistors have failed (at least one). When this happens there is DC voltage present on the speaker line which will cause the speaker voice coil to heat up like a light bulb. This is not good for the speaker and will cause it to fail. To prevent this, the Amp will detect this DC voltage and shutdown the output.

3) The speakers have failed creating short circuit on the outputs - In this case either the speaker wires have crossed or the speakers have failed. Since the Amp is expecting a particular “load” for the speakers, a short circuit will create too much of a load and the Amp will work too hard drawing too much current. This too is detected and will cause a shutdown.

These are the main causes of protect mode.

Hope this helps,


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That's an awesomely comprehensive explanation.... Thank you. Do you happen to know if there is any other way to reset the unit or fix the problem besides taking it to a Denon specialist ( as advised under " Troubleshooting" in the manual) surely they don't use a special Denon Tech magic wand.... Do they)?? ? I have the same issue with my PMA720AE Amp. It can't be that big a fix.!?


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Hi @ Biker MacBikeFace,

It may or may not be a "big fix". Only testing can determine that.

Here's a link to the service manual for your receiver which should be of some help.

Only p.13 section 2.2 of the manual you’ll find the flow charts for the red light protection mode. Depending on which condition is being shown the problem is either in the power amp circuit or the temperature detection circuit.

After that you’ll have to use the schematic diagrams found on p.21/22 to determine where the fault lies.

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