It is important to understand a key difference between analog TV and digital TV. With analog TV, the pictures could have lots of snow or lines, but there was still a picture. But with digital TV, you either have a picture, or you have nothing. As long as the TV set has enough digital information to build a picture, the picture will be near perfect. However, if the TV set doesn’t have enough digital information to build a picture, it will display a black screen. This doesn’t mean that there is no signal to the TV; it just means that the signal isn’t good enough for the TV set to build a picture that you can view. This can happen with low signal levels as well as with high signal levels. Too much signal is just as much of a concern as too little signal. When the signal is too high, it can overdrive the TV tuner, which creates distortion that blocks the digital signal. In either case, the TV set can’t build a picture, so it displays a black screen.
There are a number of troubleshooting steps you can take if you are missing one or more channels. But, before you start, it is recommended that you go to www.antennaweb.org, www.dtv.gov, or www.tvfool.com to get a listing of channels available in your location. Each of these sites will display the information slightly differently, but they are all excellent resources to find out what channels can be viewed in your location.
The channel listings provided at the above Web sites will also indicate if one or more channels in your area are still broadcasting in analog. The CM7001 is capable of viewing digital ATSC signals and Clear QAM digital channels. It cannot view older analog NTSC channels. Analog channels can be viewed by connecting your antenna directly to the TV set.
If you are connected to a cable television network, they will typically have analog NTSC, Clear QAM, and encrypted QAM signals on their network. The CM7001 will only be able to view the Clear QAM channels. The analog NTSC channels on a cable television network can be viewed by connecting the cable directly to the TV set. The encrypted QAM channels can only be viewed with the set top box provided by the cable operator. Check with your cable operator to see what channels are provided using Clear QAM.
Troubleshooting loss of channels:
- If you are unable to receive a channel you formerly received, try a different channel. Sometimes, just one channel may be experiencing a problem, while other channels are fine.
- Verify that the coax cable connecting to the ANT IN connection is hand tight, and is connected to your over-the-air antenna.
- Verify that your over-the-air antenna is still in place, and does not appear to have moved. If the antenna is moved out of proper alignment, then you may receive signal loss messages on some or all of your channels.
- If your over-the-air antenna is mounted outside, make sure no water has gotten into the coax cable, and that the coax cable hasn’t been damaged.
- If you have recently added a preamplifier, distribution amplifier, or splitter to hook up more TV sets, trying removing or bypassing the additional equipment to see if any of them are causing the problem.
- Check the signal strength on your over-the-air channels. Using your CM-7001 remote control, press the green Signal button on the bottom row of colored buttons. This will bring up the Signal Bar on screen that shows the Signal Quality and Signal Strength of the selected channel. If the signal quality is below 70%, or the signal strength is below 40%, you may experience video drop outs, video tiling, and image freezing.
- Your over-the-air antenna may need to be adjusted. Contact your local retailer for assistance. If you want to try adjusting the antenna yourself, refer to any instructions accompanying the antenna, or visit www.antennaweb.org for antenna recommendations and general information on antenna alignment.
- Make sure you are providing enough signal to your TV set. The channel listings available from the sites listed above will indicate what type of antenna is recommended, or the expected receive signal strength, for each channel on the list. To receive the weakest channels, it may be necessary to use a larger antenna to pick up the signals. It may also be necessary to use a preamplifier ensure enough signal to the TV set.
- Make sure you are not providing too much signal to your TV set. The channel listings available from the sites listed above will indicate what type of antenna is recommended, or the expected receive signal strength, for each channel on the list. If there are strong channels and weak channels both listed, it is possible that a high gain preamplifier may amplify the signal too much, overdriving the TV tuner and blocking the reception of the weaker channels, or causing the loss of all channels.