If TVGuardian LT seems to have learned your remote control mute code, but pressing TST does not mute your TV (or audio receiver), check for these things:
The IR cable eye is not over the IR sensor on your TV (or audio receiver)
Sometimes, locating the IR sensor is easy, other times it is not. You may have the IR eyes close, but not quite close enough. Move the IR eyes around the area on your TV where you think the IR sensor is located and press and release the TST button. Make sure the IR eyes are nearly touching the TV when you do this. If you find the IR sensor spot, tape the IR eye over it.
If you're remote control stops working, you might want to move the eye slightly to make sure it doesn't interfere with your TV remote.
Special Mute Learning Instructions
If you’re having trouble getting your TV or audio receiver to mute, try one of these special settings:
Dual Mute Code Mode: Sony TVs, and perhaps others, require the mute code to be sent twice. Select either IN1 or IN2. Press and hold the LRN/TST button until IN1 or IN2 blinks. Press the H/D button (it should light up). Point your TV remote at the front side of TVGuardian and press the mute button. The IN1 or IN2 light should stop blinking. Test the mute.
Half Mute (Soft Mute): Follow the instructions under Dual Mute Code Mode, except, instead of pressing the H/D button, press the R button (it should light up). Then complete the Learn and Test steps.