Digital cable is the cable format of choice for Americans, particularly after federal law phased out the analog "over-the-air" broadcast format in 2009. Because digital television stations broadcast over a different format than analog ones, signal problems manifest themselves in different ways and require other approaches to troubleshooting than the one required for analog television.
Recognizing Digital Cable Signal Problems
Signal problems associated with digital cable service manifest themselves in different ways than signal problems associated with analog cable. Whereas analog cable signal degradation generally causes static or popping on the screen, poor digital cable signal usually results in pixelization or "macroblocking" -- the term describing the puzzle-piece-like effect that breaks out over the entire screen. The picture may also freeze altogether and you may hear intermittent audio or no audio at all.
Reset Digital Cable Equipment
As noted, digital cable service is typically used in conjunction with digital cable equipment, most notably a digital cable converter box. The first and often most effective troubleshooting step to resolve digital cable signal problems is to reboot your Comcast digital cable box by removing its power cord for 30 seconds and plugging it back in. After the box reboots, check your Comcast cable signals to see if the picture has returned to normal.
Isolate the Problem
Since there are far more digital TVs on the market today than analog ones,the picture and audio problems you are experiencing may seem the result of a degradation of your Comcast digital signal when they are actually the result of problems with the TV generally. To determine if this is the case, check the other component devices that are connected to your TV -- DVD players, gaming systems, Blu-ray players -- and look for any of the same signal problems. If you notice the same issues, the problem is more likely your TV than your Comcast cable signal. If the problems appear to be confined to Comcast channels alone, however, the TV is likely not the source of the problem.
Among the most common causes of a degraded cable signal is a loose coaxial cable connection, obvious as it may seem. Check the coaxial cable that attaches your wall cable outlet to the coaxial input on either your TV or your Comcast digital cable box and make sure the fittings on either end of the cable are just hand-tight, no tighter and no looser. If the picture does not improve after tightening the cable, it is always useful to remove the cable completely and check the copper needle running through the middle of the cable for any bending or damage. Replace the cable if it is badly damaged, but if the signal does not improve at this point, it will be necessary to contact Comcast technical support and report the issue to them.