Subwoofer doesn't turn on

I suppose you could, but you are talking about a driver (speaker) that was not designed for that cabinet size and amplifier used in the Kenwood, There are differences in speaker design besides power rating and impedance.

Several possible answers. First - is that the Yamaha has a fault that is sending a signal with too much power on it. And the sub detects this and switches off.
Second - either the Receiver or Sub is switching off when no audio is present. A setting problem?
Third - the sub has a fault, possible overload, and goes to standby for safety.

If the cable is really old try getting a new one. I would recommend either a monoprice cable or a mediabridge cable both are as high quality and much cheaper than a monster.

After making sure that your subwoofer is receiving power, as most models have their own amplifier, make sure that it actually is turning on. There is a possibility of a faulty power switch. Lets rule that out first.
Once the switch is on and the proper power connection is verified, turn your attention to the setup menu on your receiver. Navigate to the LFE/Sub output level. Adjust it up all the way. Then navigate to the crossover setting. Turn it up all the way. If the subwoofer also has it's own control panel including a crossover, turn that up all the way as well. Then with an input on the receiver that has a subwoofer output set up such as for DVD, play some audio. Or likewise you can also use the receivers' test tone capability that will pan each channel individually with a wide band pink noise signal that also includes a signal sent to the subwoofer output.

If this procedure does not produce results then send me a message including your subwoofer model and your observations of your systems' operation.

UNHOOK YOUR SPEAKER WIRES FROM AMP/IF THE GREEN LIGHT STAYS ON IT IS ONE OF
YOUR SPEAKERS.

Subwoofer output: Hold the (AM-) button down for at least two seconds. You can do this function when "SWPRE" in is set to . The SWPRE (Switching Preout) Switches the preout between rear output ("R") and subwoofer output ("SW").

Disconnect its input cable to see if a true lack of signal lets it go to sleep. If not, it has a bug. Otherwise, you probably have some sort of signal present on the sub cable.

Hi, I was able to take care of this issue by talking to Onkyo tech support. They diagnosed over the phone and concluded that the receiver set the volume for the sub way too low (-12), therefore sub was not receiving the input and was doing what it was supposed to be doing. They walked me through manually increasing the volume and now everything works great.  Good luck! I hope this helps.

It sounds like your subwoofer acts as a receiver in its own right. Many low-budget home theater systems act this way, and it may in fact have a Dolby Pro Logic II encoder in it. Your best bet is to hook up either the speakers it came with, or purchase speakers from your local audio visual store. Check its power rating per speaker (in watts) in your manual, and purchase speakers that are rated for it.

The "red and white" input you mention are RCA connectors, and should allow you to connect a source to your system. If you have any more specific questions, please post them here.

"Sub-woofer output not working" problem, and notify you when a new solution is offered.
Press the setup key on the front of the receiver
Select the subw setting
Move the multicontrol knob until the sub woofer is on
Turn off the receiver and turn back on- the subwoofer should be on

The operator manual can be downloaded on the web site--- free

http://www.retrevo.com/support/Kenwood-VR-507-Receivers-manual/id/480ag219/t/2/