How to Troubleshoot Video Problems
By Steve Faber
Few things can be as frustrating as picture problems. You get your system all ready to go, flip the switch, and WHAM! One or more channels look terrible. The good news is that the majority of video problems can be traced to just a few causes. Most problems are comprised of the following:
Horizontal bars rolling though the picture
Vertical bars rolling through the picture
Herringbone pattern (diagonal lines through picture)
Lower channels look fine, upper channels are not
These six are the main symptoms you’ll find when seeing video problems. Thankfully, most are fairly easy to fix.
Snow is caused by inadequate signal strength at the tuner. It’s usually caused by:
1 Splitting the signal too many times.
2 A weak signal from the antenna or cable company
3 A very long cable run
If the signal is snowy at all your TVs, especially if you have more than 4 TVs, you probably need an RF amplifier. Check the strength at the demark (service entrance). If it is fine there, add an amplifier before the splitter. Make sure to use a quality unit with good bandwidth (out to at least 1000MHz). If you have digital cable or a cable modem, get an amplifier with a bidirectional return path to allow for communication back to the cable company. If the picture looks bad at the demark, contact the cable company.
If it is bad at only one TV, you may have a bad cable between the splitter and the TV or a very long run of cable. You can amplify just that run.
Horizontal Rolling Bars –
Horizontal rolling bars are caused by DC power getting into the cable system. To fix it, disconnect the TV from all other components in the system. If the bars disappear, add the other components back in until the bars return. When you find the offending component, use a DC blocker to eliminate the DC power path to the system.
Vertical Rolling Bars –
Vertical rolling bars are caused by AC power getting on the cable line. The best fix for this is to use a ground breaker. A ground breaker eliminates the electrical connection between the TV and the cable system. A ground breaker is also the main fix for a hum on your audio system’s speakers.
Ghosting is caused by the tuner receiving identical signals at slightly different times. It can be caused by your TV receiving a local station broadcasting over the air and via the cable system at the same time. Make sure you are using good quality RG-6 coax cable and good compression fittings. Replace any low quality cable splitters or combiners with high quality units. Make sure they are tight also. This will also cure another cause of ghosting, signal reflection inside a poor cable.
Ghosting can also be caused by multi-path interference on an antenna system. This is especially true in an urban environment with lots of hills and tall buildings. To combat this, use a very directional antenna aimed directly at the desired station.
Herringbone Pattern –
A herringbone pattern is caused by radio frequency interference from other stations transmitting on the same channel or adjacent channels, powerful radio signals, computers, etc. Another common cause is being equidistant from two transmitters operating on the same channel.
In short, this can be caused by just about any sort of RF radiation at the correct frequency. Really great shielding found on high quality cables helps to combat this. If you are getting this interference while modulating an A/V source on a certain channel, try switching to a different channel.
Poor Upper Channel Reception –
Poor Upper Channel Reception is caused by poor signal strength on the upper channels. Use an amplifier with a tilt compensator that allows adjustment of the upper channels relative to the lower channels. This will prevent overdriving the lower channels while providing the upper channels with enough gain. Also, check to see if all components in the RF system are rated to at least 1GHz and RG-6 or RG-6Quad shield cable is being used throughout.
Bio: Steve Faber has almost 15 years in the custom installation industry. He is a CEDIA certified designer and Installer 2 with certifications from both the ISF and THX. His experience spans many facets of the industry, from the trenches as an installer and control systems programmer, and system designer, to a business unit director for a specialty importer of high end audio video equipment, a sales rep for a large, regional consumer electronics distributor, and principal of a $1.5M+ custom installation firm. He currently is senior sales engineer for Digital Cinema Design in Redmond, WA. For more on how to get the best video in your home or theater see Home Theater Video
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