In this discussion, I would like to share with you an earlier experience during my late teens on how to repair and diagnose faulty guitar, speaker, power, microphone, and other small signal cables. I refused to just throw them away. After acquiring some basic skills in using VOM (volt-ohm-milliamp) meters, DVM, DMM (digital multimeters) and soldering irons, I often made basic and sometimes crude repairs to some of the above-mentioned items. For an example, I would take a faulty guitar cable or long power cord that usually contained two or three conductors (ground, positive, and negative wires) and check for continuity and/or resistance on each line. Through this procedure, I would determine if there was a short or open between both end–point connectors and each conductor. If there was continuity, and/or very small resistance (on the order of 1-3 ohms) I would assume that part was good. I would usually find an open line or loose terminal or connector. When I found open conductors on the more expensive and longer cables (15ft or more), I would often cut the cable in half to isolate the bad or faulty part. Next, I would strip the insulation from the edges of the good and faulty sections and make new continuity and /or resistance checks. I would continue this process until the faulty section was isolated. This was literally an early application for me in the half-splitting trouble shooting technique even though I was not aware of the terminology at the time. Sometimes, I would take all those good sections and solder new connectors onto them, creating a variety of lengths of “new” cables.
During this period, I also learned that bad soldering joints could lead to faulty connections. You could easy get irritating hums from poor soldering connections and faulty terminals, which would be undesirable in musical and sound systems. As part of the soldering process, one must use the proper powered soldering iron and solder (i.e., acid or rosin core, etc.).
To improve upon my earlier troubleshooting techniques, I would probably use a digital pulser and digital tracer pen that was described in the trouble shooting section of chapter 6 of our Electric Circuits textbook. A digital pulser sends current into a circuit and the digital tracer pen picks up the signal via the magnetic field produced by the pulser current. When the tracer pen no longer receives a signal, the fault usually lies somewhere in that area. Many auto repair technicians make use of this valuable and relatively inexpensive tool.
Poor soldering on a printed circuit board could cause open, shorted, or intermittent connections and operation. Also, one could use the digital pulser and tracer to diagnose these types of faults. Reheating existing soldering connections could also alleviate the effects of poor soldering joints. During this process, one could use a solder sucker tool to remove excess or unwanted melted solder. Sometimes various lengths of jumper wires may be soldered onto the circuit board to make new and/or improved connections.
Floyd, Thomas, L. and David M. Buchla. Principles of Electric Circuits. Available from: ECPI, (10th Edition). Pearson Education (US), 2019.