Basic electronic troubleshooting from circuits to stereos

When electronics fails to operate properly, the engineer or technician must locate the fault and fix the problem. Often the actual repair is relatively easy but the initial diagnosis may be difficult. Certain diagnostic procedures are unique to electronic systems but often the logic and reasoning are no different than in the diagnosis of a lawnmower, bulldozer or any other machinery.

There are two aspects to the diagnostic routine: logical analysis and use of knowledge specific to a particular type including make and model of electronic equipment. Sometimes the technician can instantly see the problem – A GFCI LED indicates it has tripped out and needs to be reset or the breaker in the entrance panel has interrupted the power supply. Other problems are more subtle and may take hours to resolve.

One lessons is when there is a difficult diagnosis, don’t think you are going to find the problem in five minutes. Some situations require extensive Internet research, close examination of block diagrams and schematics and consultation with tech help and applications engineers. Then specialized test equipment such as an oscilloscope and function generator may need to be deployed.

It is to be emphasized that when a diagnosis is elusive the operator may be able to provide information that points the way. For example, the problem may have begun during an intense electrical storm. In that case, look for an open low-current fuse that protects a circuit board, or perhaps visual evidence of a burnt component.

One effective troubleshooting procedure is known as “divide and conquer.” To illustrate, if an ac electrical receptacle is out and appears to be part of a parallel string, daisy-chained from the entrance panel, go to the midpoint of that run. Observing whether there is voltage or current at that point will cut in half the segment containing the fault. Go to the midpoint of the bad segment, and the area of concern will again be cut in half. This technique can quickly locate the fault, usually a loose or burnt termination. It is much faster than removing each wall plate, pulling each receptacle and checking in succession.

That simplistic example can be applied to much more complex systems, whenever there are series- or parallel-connected components, circuits or stages.

Intermittents are difficult to resolve because they can only be diagnosed while the system is in failure. Many intermittents are temperature related, and may be brought out by hovering a soldering iron (not too close!) over suspected components. Similarly, a volatile spray known as electronic parts chiller will selectively cool intermittent components to see if that temporarily restores operation.

For a difficult diagnostic puzzler, try to phrase it in the form of a question including make, model and error code if any. Type it into an Internet search bar. There are countless tech forums, tutorials, manufacturers’ documents and so on and it is likely that an answer will be found.

In stereo equipment, the output of a stage in a good channel can be connected to the input of the following stage in the bad channel to see if operation is restored. This technique can be used to good effect in conjunction with divide-and-conquer. A similar procedure is useful whenever there are identical subsystems or if you happen to have on hand a working model of the faulty equipment. Using similar types of logic, you can work more efficiently than performing a laborious series of component substitutions.

Stereo sound systems generally consist of two channels each terminating in a single speaker or tweeter-woofer combination. The concept is simple. In the recording studio or on-stage in a live concert auditorium, two microphones are placed some distance apart. The spatial separation lets the two microphones pick up different audio signals, one perhaps for singing while the other focuses on instrumentation. These separate sound streams go into what are known as left and right channels. They are amplified separately and recorded as discrete analog or digital streams.

These two separate “grooves” are manufactured into discs or tapes, or broadcast as separate channels. The end user typically inserts a CD into a stereo player and the two channels are routed through separate amplifiers and without mixing fed to dedicated speakers or tweeter-woofer assemblies.

The playback speakers are placed to simulate the locations of the microphones in the original recording facility. The result is a striking sense of immediacy and perception of space for the listener.

Phasing is critical. All speakers should compress the air toward the listener simultaneously, as opposed to the situation where one speaker pushes while the other pulls. The latter arrangement makes for a muddy sound where the true stereo effect is lost.

There are several ways to phase speakers correctly. A C cell can be connected to each speaker and the polarity can be ascertained visually by watching the cone move in or out. Another way to go is to try both hookups and see which one sounds better. Reverse the two wires on one (not both) speakers and you will be surprised how much better the correct phasing sounds.

High-end stereos have a phase switch for one of the channels. You can make your own phase switch by getting a four-way switch at the local hardware store and installing it anywhere in line between one of the channel outputs and the speaker.