I bet most Tape Op readers who own a soldering iron also have a digital multimeter (DMM), and they've learned at least the basics of diagnosing misbehaving instruments, amps, pedals, preamps, processors, and whatnot. Often enough, the fix is nothing more than an intermittent solder joint or a failed component in a circuit. A DMM with a diode-test function can go a long way in finding these kinds of faults. Unfortunately, checking every component for its expected value can be tedious work. A much quicker strategy is to work backwards through a circuit, one stage at a time, injecting a signal at the input of each stage and comparing it to the signal at the final output, until the faulty stage is identified. For this, a signal generator and an oscilloscope are needed. Lucky for us tinkerers, the price of test equipment has dropped significantly in the past decade or so. There are now countless digital storage oscilloscopes (DSO) with an onboard arbitrary waveform generator (AWG) priced lower than a Fluke DMM, for example. Granted, a low-cost DSO won't have the resolution, accuracy, and features necessary to measure the performance of a high-fidelity audio device, but even the cheapest scopes can help us determine which stage in our device is busted. I own several analog and digital scopes ranging in price up to $1,000; but the one I use most often is my $240 OWON HDS2102S, a handheld 2‑channel DSO, DMM, and AWG that's slightly bigger than my Fluke DMMs. Its usable bandwidth is truly 100 MHz with a 500 MSa/s sample-rate in single-channel mode, and approximately 70 MHz at 250 MSa/s in dual-channel. Its 3.5-inch color TFT screen is very legible from all angles, the front-panel controls are easy to use, and a built-in Li-ion battery provides 6 hours of power between charges. For higher-resolution waveform display, as well as for sharing captured data and images, I connect the scope's USB Type-C port to my Microsoft Surface Pro running the free DS-WAVE application. ••• Another category of useful troubleshooting tools that has dropped steeply in price are thermal imaging cameras. I have an HIKMICRO B10 that I purchased several years ago for $400. Its resolution is 256×192 at a 25 Hz refresh rate, with a temperature range of –4°F to 1022°F. A newer B01 model is currently $300 on Amazon, and it supports Wi-Fi connectivity to HIKMICRO Analyzer software running on Windows and Android. The older B10 has USB Type-C only. Both models are shaped like a fat squirt-gun, with a 3.2-inch color TFT screen that is bright enough to view outdoors. The fixed-focus infrared lens isn't capable of imaging details closer than a foot in distance, but "Fusion" mode overlays a standard optical image with the infrared one, which makes it possible to identify thru-hole components on a circuit board. An optional $100 macro lens is necessary for pinpointing hot spots on a surface-mount board. A component failure will often lead to that part (or an adjacent one) overheating. Therefore, the first step I take when I'm troubleshooting a circuit is to image it with my thermal camera, and that can highlight the section of circuitry that I should investigate more carefully. For example, when one of my converters was acting intermittently, I was able to quickly find a rectifier diode in the power supply that was overheating due to a short condition — an easy fix. I don't do a lot of electronics repair, but I estimate that my thermal camera has still saved me dozens of troubleshooting hours; it has definitely paid for itself. Also, it's a downright dependable "Doggy Doo Detector" too – especially in the fall, when I'm picking up after my dogs around fallen leaves and browning grass.