When power button turned on, receiver powers up

Press and hold the "straight" and "Tone control" buttons and press power. This should release the protect lock that the receiver is in. If it shuts back off immediately, then you most likely have a blown amp that will need to be repaired.

Have you provided adequate ventilation?
May be your receiver is running hot and when there is loud volume it is obviously getting overloaded. There are no fans inside 674, the only way to provide good ventilation is to keep the top of receiver clear for atleast 6 to 8 inches.

Hope that helps.....

The amp protection circuit has been activated. Remove the power cord from the wall outlet immediately. Disconnect all speaker cables and input sources, and leave the AV receiver with its power cord disconnected for 1 hour. After that, reconnect the power cord and reconnect an input and a pair of speaker wires onto the unit. If the receiver still does not turn on than you will have to bring it in for service. Turn up the volume and if the receiver doesn't shut down, power off the receiver and add another pair of speakers. Power up the unit again and turn up the volume. If it doesn't shut down, power off the unit again. Now connect all your input sources and turn on your receiver. If the unit shuts down again, your unit will need to be further serviced at an authorized Onkyo service center.

The amp protection circuit has been activated. Remove the power cord from the wall outlet immediately. Disconnect all speaker cables and input sources, and leave the AV receiver with its power cord disconnected for 1 hour. After that, reconnect the power cord and reconnect an input and a pair of speaker wires onto the unit. If the receiver still does not turn on than you will have to bring it in for service. Turn up the volume and if the receiver doesn't shut down, power off the receiver and add another pair of speakers. Power up the unit again and turn up the volume. If it doesn't shut down, power off the unit again. Now connect all your input sources and turn on your receiver. If the unit shuts down again, your unit will need to be further serviced at an authorized Onkyo service center.

I had this problem also and discovered an easy way to trick it into powering on: Click the power button, then within 1 second of the receiver powering off, click the power button again. The receiver should stay on this time. This works with both the button on the receiver and the remote control.
I would like to know what causes this problem and whether or not I should be concerned about damage being done. I assume this is a power protection. I haven't tried plugging this receiver into a different power socket to test, but I don't think the power plug is the problem. Note: I have the subwoofer plugged into the power plug on the back of the receiver.

Most likely bad output transistors and a couple of resistors. mp1620 and mn2488 are the part #s for the transistors. If you take it to a repair shop you are looking at spending $100-$130

power output shuts ......send to service

r this one: Switc off your receiver using the main power button on the front face. Hold the the Effect button and the Direct button, and turn the main power ON.f it ain't working, try this one: Turn your receiver ON and, while holding down the [VCR1] button, press the [STANDBY/ON] button. "Clear" might appears on the display and your receiver might enter Standby mode.
Hope it does.. With your receiver in the Standby mode, hold on STRAIGHT (EFFECT) on the front panel and press STANDBY/ON.
* The ADVANCED sETUP menu appears in the front panel display.ress STRAIGHT (EFFECT) to select the desired setting.
RESET = To reset your receiver to its factory presets.
CANCEL = To cancel without making any changes Press STANDBY/ON to confirm your selection.
* If you selected "RESET", your receiver is reset to its factory presets and switches to Standby mode good luck

shaun

www.eserviceinfo.com/downloadsm/28790/Onkyo_HT-R500.html

Unplug all the speaker wires first, then unplug the unit from the wall for at least 24 hours, The plug back in without the speaker wires or anything else plugged in. Then see if it goes to the protection mode. If it does not, plug in each speaker at a time, and see if any speaker, when hooked up, makes the receiver shut down. If it does shut down, My friend, I'm afraid you will need to take this unit into a repair shop, OR get a new unit. Good Luck