This is the solution I came up with to MUTE and UNMUTE my tv (through the receiver) using voice commands with Echo/Alexa without changing inputs or powering other devices off.
MY DEVICES: TV, AVR (Sony STRDN1040), Verizon cable set top box, SmartThings hub, Harmony hub, Amazon Echo.
This assumes you already have Alexa/Echo set up correctly to command your activities. (eg. “Alexa, Watch Netflix” – turns on tv and receiver to correct inputs.)
Go into your Harmony app and do the following:
Change the TV, receiver and set top box to the following power setting:
Change Device Settings > Power Settings > I want to keep this device on when switching activities and only turn off if I press the off button.
Save those and then you want to create another activity.
Add Activity > Create “Custom” activity.
I named mine “Shut Up” because I think there was an issue with Alexa recognizing/confused using “Mute” and “Silence”. You might have better luck with another name, but that was my experience in trying those first.
Add your receiver as the only device for this activity. When it asks which input to select, “I do not set an input”. Save.
Select the Activity you just created, then choose “Customize this Activity”. Add a step, select your receiver as the entertainment device, then chose the command “mute” from the drop down list. Save.
Create another activity exactly like you just did above - I named this one "Sound” – and customize it the same way adding the mute command.
NOTE: If you already have your Harmony set up with SmartThings + Echo, you will need to unlink and delete all the Things, then re-add them back in.
Now I can say “Alexa, turn on Shut Up” and it will mute, then I can say “Alexa, turn on Sound” and it will unmute. The inputs and power remain on and correct without any changes. If I want to turn off the TV, I simply tell her to and everything shuts off. Hope this helps- I couldn’t find a solution anywhere for a simple mute command.