Basic CCTV system troubleshooting
September 2003, CCTV, Surveillance
Troubleshooting a CCTV system is an art form. Whether the problem occurs during initial system installation or after, most installation and service managers fear troubleshooting procedures.
Many view the troubleshooting process only as an added expense above the overall system operation cost. However, by following a few basic guidelines and using some basic test equipment, even a novice technician can more easily solve CCTV system problems.
Diagram the system
One of the first steps in troubleshooting a system is examining the system block diagram. Doing so will allow the service technician to obtain a basic understanding of the equipment layout. This step is especially important when systems include different monitoring locations. Following the video and data paths of an entire system is essential for proper troubleshooting procedures. Understanding these paths will help determine, for instance, the proper terminations of all signals. Remember, it is much easier to understand a system on paper than to understand that same system in the field. Examining the diagram also takes less time than walking through the system in the field.
A technician may have to gather a good deal of information about the system in order to troubleshoot the problem and service the equipment. Some of the following questions, particularly the first few, may seem very basic. However, they are the perfect starting point for troubleshooting any system.
1. How old is the system?
As we all are aware, even the best electronic equipment eventually wears out and fails. The average life of most system components is about seven years. Components such as pan-and-tilt units, analog recording devices and monitors have shorter lifespans and will require more maintenance.
2. Has the same problem previously occurred?
The reoccurrence of a system failure - the same component at the same location, is usually associated with power, power surges or improper installation procedures. Low AC input voltages and excessive voltage have contributed to many such system failures. Before blaming the equipment, remember the odds of the same system component having the same problem at the same location are very high.
3. Has anyone tried to repair or troubleshoot the system?
The simple yes or no answer to this question may completely change your troubleshooting methods. Electronics and electronic equipment are logical; human behaviour is not. If a previous technician has shorted a terminal with a screwdriver or adjusted the control potentiometer without knowing the functions, it can add to your headaches. So it is a good idea to ensure no one else has tried to fix the problem. If you find someone has, you must perform a complete check of all connections and settings before moving forward. It may also be a good idea to speak with the previous technician regarding the problem, but proceed with caution. One person's impression of the system trouble may or may not be accurate. System technicians must rely on the information at hand, but they must also verify this information. Assumptions have led to excessive troubleshooting time and many failed attempts at system repair. Asking the following questions can help limit the possibility for unwarranted assumption.
4. What type of video cabling is installed?
5. Are there video amplifiers installed in the system?
6. Is there more than one video monitoring location?
7. Who installed the cables and when?
Divide and conquer
A basic rule in the art of troubleshooting is to divide the overall system into sections. This system dissection will ensure you do not miss any areas, and it also usually leads to a quicker solution to system problems. I use the three Cs when dividing the system: cameras, communications and control systems. Many times the major problems are found within the first two sections. Third section problems usually consist of simple termination and programming errors.
An estimated 65% of all system problems are caused by cable, connections and termination. Problems associated with power, power surges and excessive AC voltage range from 20 to 25%. That means only a maximum of 10% of system problems stem from equipment failures. The rest are caused, for the most part, by human error. However, if you supply your service technicians with proper tools and education you will find that your return on investment both in time and in money will far exceed expectations.
Tools and test equipment
We can no longer afford to guess at what system problems may be. Technicians must be able to properly evaluate the symptoms and make the correct decision for system repair. Troubleshooting requires some basic tools, which range from a simple screwdriver to an oscilloscope. The following is a basic list of equipment useful for system troubleshooting.
1. Volt-ohm-meter (VOM).
2. Video oscilloscope (20 MHz).
3. Set of screwdrivers.
4. ND3 lens filter (back focusing).
5. Test monitor.
The goal of all troubleshooting procedures is to properly reproduce acceptable video images on all monitor displays, have proper system control and provide an acceptable recorded image of this information. When troubleshooting video problems, an oscilloscope in particular can assist you towards this goal. This instrument temporarily converts variations in electrical signals from the camera into a visible waveform, and the information can be tracked through the entire video loop. With the help of an oscilloscope, what appeared to be a 'no video' problem may be exposed as excessive video caused by an auto-iris lens that has latched wide open. The ability to view and analyse video waveform will reduce troubleshooting times significantly. It not only can reduce confusion but also may help in preventing future problems, such as improper video termination, improper auto-iris lens level set-ups, ground loop problems and improper cabling.
A basic waveform consists of sync information, blanking information and video information, all of which when properly understood help in determining problems in a video system.
Training and installation
Following proven initial installation procedures is the best way to reduce the need for troubleshooting a system. Proper training in installation can eliminate many system problems. Simple mistakes, such as forgetting to add 75 Ω terminations or installing the incorrect video cable, can create nightmares. Most manufacturers now suggest the appropriate cable and connector types for their equipment. The standard recommendation for video cable is cable with copper centre conductors and a minimum of 95% copper shielding. The use of aluminium-shielded cable for video is now forbidden by all system manufacturers using baseband signals. Many manufacturers also state that only two-piece or three-piece crimp-on BNC connectors should be used. The days of BNC twist-on connectors are long gone.
Manufacturers are revising many of the cable distances suggested for video and data as well. The main reason is the increasing use of digital equipment. Digital equipment in most cases requires smaller operating ranges than its analog counterparts. Therefore, many manufacturers have shortened their operating cable distance to conform to the new digital requirements. All of this will affect installation as well as system troubleshooting parameters.
A few CCTV manufacturers now offer courses on system troubleshooting and repair. For the most part, these manufacturers have found that their training has helped reduce service calls related to simple system problems. This reduction has freed up their technical staff to answer the more complex questions, which improves their overall customer service programs.
This article was first published in the August 2003 issue of Security Technology and Design. ( www.simon-net.com)
About the author: Robert (Bob) Wimmer, president of Video Security Consultants, has more than three decades of experience in video system design and troubleshooting. He can be contacted via e-mail at CCTVBOB@aol.com