Nakamichi Blond Moment

The issue you're describing with your Nakamichi NA6605 head unit muting itself after installing new Infinity speakers could be caused by a few different factors. Let's go through some troubleshooting steps to help pinpoint the problem:
1. **Impedance Mismatch:** You mentioned that you replaced the factory speakers with Infinity 6x8 REF-8632cfx speakers. These Infinity speakers have an impedance of 3 ohms, while the original speakers were likely 4 ohms. This difference in impedance could potentially cause issues with the head unit's output stage. Some head units are designed to handle a specific range of speaker impedances. Make sure the Nakamichi unit is compatible with 3-ohm speakers. If it's not, this impedance mismatch could indeed lead to the behavior you're experiencing.
2. **Wiring and Connections:** Double-check all your wiring connections. Make sure that the speaker wires are properly connected and that there are no loose or exposed wires that could be causing a short circuit. Incorrect wiring can cause the head unit to detect a fault and enter mute mode.
3. **Power Supply and Ground:** Ensure that the head unit is receiving a stable power supply and that the ground connection is solid. Voltage drops or poor grounding can lead to unstable operation.
4. **Short Circuit Protection:** Many modern head units have built-in protection mechanisms that detect short circuits or incorrect impedances. If the head unit detects a problem, it might enter mute mode to prevent damage. Check the head unit's user manual to see if it has any relevant protection features.
5. **Head Unit Settings:** Check the Nakamichi unit's settings, especially those related to speaker impedance or output settings. Some head units allow you to adjust output settings based on the connected speakers.
6. **Firmware Update:** If there's a firmware update available for your Nakamichi head unit, consider updating it. Firmware updates can sometimes resolve compatibility issues.
7. **Test the Speakers:** To rule out the possibility of a faulty speaker causing the issue, you can temporarily disconnect the Infinity speakers and see if the head unit behaves differently.
8. **Professional Inspection:** If none of the above steps resolve the issue, it might be best to seek the assistance of a professional car audio installer or technician. They have the expertise and tools to diagnose and address complex issues with car audio systems.
Remember, electrical issues in car audio systems can be complex and require a methodical approach to troubleshooting. If you're not comfortable diagnosing the issue yourself, it's best to seek professional assistance to ensure a safe and accurate resolution.

Generally speaking, an amp protects itself from heat, shorts, overloads and operator exuberance by refusing to turn on or stay on.

Overloads can be from excessive periods of high output or marginally low impedance loading by the speakers; and shorts would be wiring issues or a speaker blowing up.

In your case it is obviously not heat, speaker load or excessive volume at the moment.

You could unplug it then turn it upside down and shake it to see if something metallic is rattling around inside it. Maybe open it up and sniff for burnt components, but even if you see something obvious and replace it you migh not know what the original cause for failure was, so you may just be wasting time and sacrificing new parts.

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Check the speaker wires and be sure they are not shorted. If no obvious signs, remove alll speaker wires and check system. It could be a short in the wire, a bad speaker, or a problem in the receiver.

The most common problem found on FixYa for Audio Video Receiver's is:

My receiver say's "Protect" or turns on then off. What's wrong? Seven times out of ten it is a shorted speaker or speaker wire. To determine your exact problem, the first step is to disconnect all speaker wires "at your receiver" Next: Turn the receiver back on. If your receiver still says "protect" or turns off, it needs to be serviced. If your receiver stays on; reconnect your speakers one at a time and power back up after each speaker. You may find that after reconnecting all speaker wires it works! Most commonly the small braids of wire from the + to the - have touched and have caused the problem. In some instances, you noticed the problem only when turning the volume up. either way, make sure the exposed wires to your receiver are no longer than 1/2" long and are completely under the screw down terminal or slide in. When you've found the wire or speaker with the problem, your receiver will go back into "protect" At this point, disconnect the wire from the speaker at the speaker that may be causing the problem then test again.* Note* Make sure speaker wires do Not touch each other as this Will cause a short! If you turn the receiver back on and it stays on, you now know the problem is in your speaker itself. To test your speaker, you will need a multimeter. Set it to ohms resistance and touch the speaker terminals, if there is a short internally the meter will read "1......" If it's an analog meter, it will peg to the right. There's your problem. Now, within any speaker there are quite a few possibilities as to what could be causing the problem. Most common is a blown coil and the speaker needs to be replaced. Some speakers have internal crossovers (usually floor standing speakers) and may have a shorted or burnt board (usually very visible brown burn marks on the board) and can possibly be repaired if your handy with a soldering iron. Now, if you disconnect the speaker wire at the speaker and it still says "protect" Check your wire for the obvious cut or nail thru the wire if possible. If your system has wiring that runs behind walls, you may need to use your meter again. Disconnect the wire at both ends, keep the ends separated, put your meter on ohms resistance and touch probes to the + and - wires at one side. If the meter pegs to the right or reads "1...." the wire is shorted and needs to be replaced or repaired at the short. Hope this helps.

There is a short either on the speaker wires to the speakers or the speakers are defective (some sort of a short or too low of resistance). Lastly, check to see if a stray strand of wire is not touch the left and right terminals. Any short in the network (wire, lack of insulation, staple, screw, etc. ) will cause the system to clip.

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The most common problem found on FixYa for Audio Video Receiver's is:

My receiver say's "Protect" or turns on then off. What's wrong? Seven times out of ten it is a shorted speaker or speaker wire. To determine your exact problem, the first step is to disconnect all speaker wires "at your receiver" Next: Turn the receiver back on. If your receiver still says "protect" or turns off, it needs to be serviced. If your receiver stays on; reconnect your speakers one at a time and power back up after each speaker. You may find that after reconnecting all speaker wires it works! Most commonly the small braids of wire from the + to the - have touched and have caused the problem. In some instances, you noticed the problem only when turning the volume up. either way, make sure the exposed wires to your receiver are no longer than 1/2" long and are completely under the screw down terminal or slide in. When you've found the wire or speaker with the problem, your receiver will go back into "protect" At this point, disconnect the wire from the speaker at the speaker that may be causing the problem then test again.* Note* Make sure speaker wires do Not touch each other as this Will cause a short! If you turn the receiver back on and it stays on, you now know the problem is in your speaker itself. To test your speaker, you will need a multimeter. Set it to ohms resistance and touch the speaker terminals, if there is a short internally the meter will read "1......" If it's an analog meter, it will peg to the right. There's your problem. Now, within any speaker there are quite a few possibilities as to what could be causing the problem. Most common is a blown coil and the speaker needs to be replaced. Some speakers have internal crossovers (usually floor standing speakers) and may have a shorted or burnt board (usually very visible brown burn marks on the board) and can possibly be repaired if your handy with a soldering iron. Now, if you disconnect the speaker wire at the speaker and it still says "protect" Check your wire for the obvious cut or nail thru the wire if possible. If your system has wiring that runs behind walls, you may need to use your meter again. Disconnect the wire at both ends, keep the ends separated, put your meter on ohms resistance and touch probes to the + and - wires at one side. If the meter pegs to the right or reads "1...." the wire is shorted and needs to be replaced or repaired at the short. Hope this helps.

Disconnect the speakers and see what happens. Carefully examine the speaker cables for unwanted connections (shorts).
Take a clue from when the power problem appeared. Something was moved and made the buzz a (probable) dead short.

so what is happening now?

are the speakers not functioning completely?

I was having this problem and after research on internet found that this could be because of speakers wire being short. I recheck all the connections and most likely have short due to wires being stapled on the wall and staple causing short. It is working fine now for me. Check your wires...

The very FIRST thing to check is to make certain ALL of your speakers have an IMPEDENCE of 8 OHMS. Virtually all speakers of even modest quality will include this specification on a label on the back of the speaker. You CANNOT run more than (2) TWO speakers with 4 OHMs impedence on ANY amplifier (technical discussion too long!) [NOTE: Some Sony equipment have internal overload protection systems to prevent permanent damage. However, you cannot re-set these systems yourself. Your dealer or authorized HK service center must do this.] But, before you take the unit in for service, there is one more "test": check for shorted and/or mis-connected/disconnected speaker cables/wires. Visually inspect connections at the receiver and speakers first. You might find something obvious! If everything looks okay, then disconnect ALL of the speakers; and reconnect and test them one at a time (at relatively low volume.) For example, reconnect the left front speaker, test the system; THEN add the right front, test the system,and so on, ADDING one more speaker each time - FIRST MAKING SURE EACH OF THEM HAS AN IMPEDENCE OF AT LEAST 8 OHMS! IF there is a short (or bad speaker) this will help isolate it. Hopefully one of these "fixes" will work for you. GOOD LUCK!