I have a rsb6 soundbar and sub. No power on sub.

It occurs to me that if the sub is no longer sending signals back to the unit then it won't find it. I am certain that it should be easy to have the sub repaired so that it does send out the signals.

If you are connecting the soundbar to your TV with the digital audio cable, make sure to select "D IN" using the source button on the soundbar. Bluetooth (BT) is a separate source from another device. (phone, etc.) The TV will need to be set to use the digital audio output and probably PCM format. (?) The subwoofer is preconfigured at the factory to mate up with your soundbar. (See below instructions - your soundbar includes the amplifier:)

Digital audio output setting:
After connecting an amplifier with digital audio input and
external speakers as shown, you should set an audio
output format compatible with the programme you are
watching or the device connected.
Go to "HOME" > "TV Menu" > "Setup" > "Option" >
"Terminal setting" > "Digital audio output" > select
"PCM" or "Bitstream".
NOTE
• When set to "Bitstream", Dolby Digital is output when the Dolby
Digital or Dolby Digital Plus audio formats are received. When
set to "PCM", PCM is output no matter what audio formats are
received.
• When set to "Bitstream", HE-AAC audio formats can be output
as Dolby Digital.

Yes! Use the digital audio output from the Mitsubishi TV to the soundbar! You need a digital audio cable that usually comes with the soundbar!

set sound to defoult on main receiver power of and then power on

A capacitor on the power board has blown. Take it to a shop or warranty replace if available

my sony dvd it make dest error haw can i do?

I am also having the same problem. It was working fine until we moved. Plugged it in at the new house and nothing but a red light. Sub is green though.

No adapter. Your sound bar has to have wireless built in.

It is not latching on to the soundbar transmitter. Is the locked light on the device turning on.
Wireless devices are sometimes known to drift. Is the sub silent when the soundbar power is off ?. Even then if its making this sound, the subwoofer amplifier is oscillating at very low frequency. You will need professional help and needs to be repaired.