Expert Advice

Contributor: Paul Broome
Company: Sensormatic VPD

Multiplexer Applications & Troubleshooting Guide

Troubleshooting

This section contains information on isolating problems. This is divided into two parts. The first part addresses isolating problems in a system which contains a multiplexer. The second section provides information for bench testing a multiplexer.

Troubleshooting on Site

Troubleshooting a system containing a multiplexer isn't much different than any other type of problem isolation. You need to know a few things which are specific to our multiplexers, however, most of the process is common sense. Video system problems are relatively convenient to isolate because you don't need test equipment for most problems. You can isolate using the cameras and monitors available on site. Typically, one end of all the cameras will conveniently terminate at the multiplexer, or, in the same room as the multiplexer.

If a problem is reported, there is indeed a problem. Test the system to see if you can make it fail, rather then to see if you can make it work. If it does not fail, you need to have the person experiencing the problem work through the system operation with you. Identify where they were encountering the problem. If the error does not surface at that time, work with the operator to determine what other factors come into play which could be causing an intermittent problem. Is the complete system powered from the same source? Could components be powered off from other locations? Is operation carried out correctly by all operators? Etc., etc., etc.

General Questions: Establish whether this is a new problem, or, one that always existed.

  1. Did the system ever work? Is this a new problem, or, was it always this way?
  2. Have you ever tried to use this function before?
  3. If this was a recent failure, what happened around the time of the failure?
  4. Has anyone been working on the system, or, installed any new equipment?
The operator is the best person to ask. Ask what problem they have encountered. Listen to the answers, but, don't rely on the information. Operators report symptoms. The actual problem may lie in an area other than reported by the operator. Symptom recognition: Take a quick overall look at the system. See if the reported problem is evident during your initial test. Symptom elaboration: Perform all functions of the system. Look for any additional symptoms and problems. You may uncover additional symptoms which were not reported by the operator. Often the reported problem is easier to solve when additional symptoms are revealed.

Isolating the faulty system component: No video when pressing camera button number three on a multiplexer may look like a defective multiplexer, however, it could be a bad camera, lens, cable, or, any number of other things in the system. Your troubleshooting abilities are limited by the test equipment at hand. Having a known good test monitor, camera, VCR and test cables make the job much easier. Testing on the bench in your repair shop allows easy access to all components in the system. The troubleshooting methods change from shop to field. We will discuss both scenarios. Field problem isolation: Obvious problems are just that. Obvious. No power to a monitor can be determined easily (no power light, no power cable, etc.) We will concentrate on a total test of a system once the obvious has been eliminated. Even with no test equipment available, some part of the system must be working. You can use the working parts to isolate the problem. Start by assembling a basic video system, (camera, cable and monitor.) Connect a camera directly to a monitor. Do you have a picture? This part must work before going on to anything else. If you don't have a picture, is the monitor plugged in and powered on? Is the power light lit? Are the monitor switches and knobs adjusted properly? (Intensity turned up, A/B switch in the right position, etc.) Is the coax cable connected to the right input connector? Is there video coming out of the cable? Does video still come out if you wiggle the connector? This is where the test monitor comes in handy. If you don't have video, any of the components in this small system can be bad (monitor, cable, camera.) Try a different monitor. Wiggle the coax cable to see if the video appears. (Remember that the most common problems are defective coax cables.) Try another camera input. If you are fortunate enough to be able to see the camera, does it have power? Is the lens adjusted properly? Once you have convinced yourself that you have these three basic components working properly, you are ready to investigate the rest of the system. Tee connectors, and/or, barrel connectors are good to have. Connect one of the connectors to the incoming video cable, then test a few other cables by connecting them from the input video cable to the monitor. Wiggle them at each connector end to ensure that they are really good cables. Reconnect the incoming video cable to the multiplexer camera input. Press the live button on the multiplexer, then press the largest multi-screen display button (2x2, 3x3, 4x4.) Do all the attached cameras display? If one, or, more inputs are missing, connect the known good camera into the missing camera input. Does it display properly? If so, you need to investigate the defective camera and cable input (the camera is often out of sight, far away, perhaps on a roof top somewhere - good luck.) Don't overlook the obvious. Make sure that all the cameras are selected. Press the select key, then all the cameras in order to fill the multi-screen display.

Once all the live multiplexer functions are known to be good, we need to test the tape playback capability. With duplex multiplexers, there is a test mode which will allow you to let the multiplexer directly decode its own coded VCR output. Disconnect the two video output cables which connect the multiplexer "VCR in and VCR out" to the VCR. Connect a short coax cable from the multiplexer VCR output connector to the multiplexer VCR input connector (they are right next to each other.) Press and hold the "Function" button, while pressing the "tape" button. Hold both buttons for a few seconds. The multiplexer will switch to the playback mode and display images at the rate it normally sends updates to the VCR based on the menu setting, (VCR record hrs.) With this menu setting to 2 hours, the images will update at a rate of 20 per second, (30 on some newer models) divided by the number of cameras attached. Check out all the "live" functions. You are actually testing the live and playback functions. If everything works up to this point, the multiplexer is working correctly. Press the live button to exit this test.

Before removing the multiplexer from the site, do a factory reset. Strange things which may have scrambled the multiplexers memory may be overcome by a simple reset to a known condition. See the "Undocumented Multiplexer Functions" section for information on resetting various multiplexers.

VCR Problems: Check the "Lookout" section for a quick review of different types of VCRs if you are not already familiar with this topic.