Most installed electrical systems work flawlessly for many years, the only maintenance being an occasional bulb or ballast replacement. Modern solid-state electronic equipment is also reliable but may need servicing from time to time, especially if moving parts are involved. Some specialized equipment such as fire alarm systems and elevators, especially when they have seen some years of service, can become buggy and require increasingly frequent attention. both of these items are on a hair trigger because they embody many sensitive safety interlocks.
It is almost impossible for a fire alarm system to fail to sound the alarm in event of fire, but many legacy systems are prone to false alarms which, in a public place, is inconvenient to put it mildly. And elevators possess a whole series of trouble sensors, which, as a safety feature, is highly desirable but can be problematical. An example is the door sensor. If it does not report to the control panel that all doors are closed and latched, the motor will not run and the car will not move even if it is full of passengers and stuck between floors. The door sensors are very rugged and well built but, in the fullness of time and after tens of thousands of cycles, a little mechanical play or electrical impedance can cause them to fail, putting the elevator out of service.
In both cases -- fire alarm and elevator -- specialized technicians often have to be called in because the equipment is highly complex and because there are life safety issues. But invariably the first responders are in-house electricians and it is their responsibility to stabilize the situation and evaluate available courses of action. In order to perform these functions, troubleshooting skills come into play, and in both of the above examples, time is of the essence. Troubleshooting means diagnosing why an electrical system or piece of equipment fails to perform as expected. it is primarily a mental process, though often the physical repair takes place simultaneously. Some very experienced technicians seem to work magic on an intuitive level without verbalizing the process. Others of us are still learning and we can benefit greatly by a thorough rationalization of the troubleshooting process. There are several useful approaches.
First, be in an information gathering mode. Typically, a production worker, homeowner or department supervisor will present a complaint -- "This motor isn't running right" it is very useful to question the individual. Additional information may save lots of work. "Well, its working now but sometimes it quits. I thinks it's the switch because I heard a frying sound." By drawing out the individual you can often cut to the chase, go right to the defective part where visual inspection or ohm measurement will verify the original theory and you are (perhaps) done.
A very useful technique which is used unconsciously by many technicians is to create a prioritized list based on probability that a given item may be a fault and also based on the difficulty and expense of pursuing that avenue. Let's take a very simple example. Suppose an incandescent ceiling fixture is out. Your informant says "It always worked but today I hit the switch and it wouldn't go on." You know from experience that it is probably the bulb. The correct procedure would be to put in a known good bulb. But suppose it is a very high ceiling and there is no ladder on site. That changes everything. Depending on how much trouble you have to go to get up to the fixture, you may want to entertain a less likely theory. If the entrance panel is nearby, you could check for a tripped breaker. You will probably end up going after a ladder to change the bulb, but how would you feel if you did that it the first place and it turned out to be a tripped breaker all along? The idea is simple -- prioritize a list of test procedures based on probability and ease of performing the test.
The mistake many beginning technicians make is that they think they are going to get the machine running in five minutes.
We have seen that a job specific troubleshooting technique can be devised that will outperform hit and miss procedures.
Some other troubleshooting methods --
Often electrical equipment such as a motor will make a loud squealing, grinding or thumping nose indicating bearing failure or other mechanical difficulty. But the sound is transmitted throughout the machinery so that the exact location is difficult to pinpoint. Use a long screwdriver or plastic tubing as a stethoscope to find the location.
Use an infrared sensor to locate hot spots. Periodic heat surveys with written records are helpful so that when a problem occurs, change of temperature will point to the bad component.
Electronic supply houses sell a coolant spray which, when applied individually to components on a chassis or circuit board, may temporarily restore function thus identifying the bad item
Circuit boards can develop oxidized solder joints which then have abnormally high resistance. You can apply a minute amount of resin (not acid) flux to each joint and remelt it with a pencil tip soldering iron. Similarly, slide ribbon connectors in and out several times to polish and renew connections.
When working on machinery, good documentation is a great help. If the equipment is not too old, there is probably a service manual on file, or it can be obtained from the manufacturer. It will have an electrical schematic which, on complex machinery, is necessary for orderly troubleshooting. Without this information, you can look around for burnt or damaged components but an efficient troubleshooting program is difficult if not impossible. Some manufacturers provide online service information. If that is not available, there are websites that provide free documentation including electrical schematics, such as www.eserviceinfo.com.
Use of advanced tools greatly expands the technician's body of knowledge and troubleshooting capability. Tone generator, wand and test set facilitate troubleshooting telephone systems. The oscilloscope, frequency generator, loop impedance meter, spectrum analyzer, field strength meter and similar instruments are suggested.
