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.

References

Floyd, Thomas, L. and David M. Buchla. Principles of Electric  Circuits. Available from: ECPI, (10th Edition). Pearson Education (US),  2019.