The Set 840 wireless headset system can be connected via a 3.5 mm plug into a dedicated headphone jack (which will often cut sound to the external speakers) OR to the RED & WHITE RCA audio output jacks (often found on the back of the TV, cable box, receiver, etc) and when connected in this manner they will allow for operation of both the headphones and the external speakers.
The first step is top connect the transmitter (base station) to power and the second step is to connect the audio cable to the audio source. When the audio cable is connected to an audio source that is turned on the first thing to check is that the GREEN light on the front of the transmitter (base station) comes on. This indicates that the unit has both power and is transmitting audio. Once this GREEN light comes on it is simply a matter of tuning the headphones into the right frequency. You do this by pressing the channel button on the back of the receiver. You may need to do this a couple of times. If the receiver does not pick up the audio transmission once you have pressed the channel button on the receiver you may need to try a different transmission channel. To try a different transmission channel you need to locate the channel button on the back of the transmitter and select a different channel. There are 3 options so be sure to try them all.
If the GREEN light doesn't come on or comes on and then goes away when the transmitter is plugged into both a power source and an audio source then it means that the audio signal is is too low (or not getting to the transmitter at all). The transmitter needs a nice, loud signal to work with or the internal electronics will shut off within 5 minutes if no/very little volume is detected to conserve battery life. The signal level needs to be increased before reaching the transmitter. This can be accomplished by turning up your source on variable-level outputs (TV Volume) or by increasing the signal from a fixed-level output (increasing the output level to the audio output jacks which is done through the TV set up options). Try increasing it in small increments to prevent overload which results in distortion. Also check to see that you are connected to outputs and not inputs. You may also try to connect to a cable box (or DVR, HD receiver, etc) and its audio outputs or through a headphone plug.
The other lights that appear on the transmitter (base station) are the battery charging indicator lights. There is one light to indicate charging when the headset is in the charging cradle and one light to indicate charging if a battery is in the side charging slot. These lights will light up RED when the battery is charging and turn GREEN when the battery is fully charged.
There are three lights are on the left hand side of the transmitter (base station) and these indicate the frequency boost functions. If the frequency boost function is not activated then no light will appear. If the frequency boost function is activated then the light will appear to indicate which level (low frequencies, mid range frequencies or high frequencies) is being boosted. To change from one level to another simply push the frequency boost button.