Yueke’ Blog

Equipment for most troubleshooting task

• A dual-trace oscilloscope. It’s best to have one with a sensitivity of 1 or 2 mV/cm and a bandwidth of at least 100MHz. Even when you are working with slow op amps, a wide-bandwidth scope is important because some transistors in “slow” applications can oscillate in the range of 80 or 160 MHz. Of course, when working with fast circuits, you should to commandeer the lab’s fastest scope. Sometimes a peak-to-peak automatic triggering mode is helpful.

• Two or three scope probes. They should be in good condition and have suitable hooks or points. Switchable 1X/10X probes are useful for looking at both large and very small signals. You should be aware that 1X probes only have a 16- / 20-MHz bandwidth, even when use a 100MHz scope. When you use a 10X probes, be sure to adjust the capacitive compensation of the probe by using the square-wave calibrator.
• An analog-storage oscilloscope. Such a scope can be extremely useful, especially
  when you are searching for an intermittent or evanescent signal. The scope can
  trigger off an event that may occur only rarely and can store that event and the events that follow it. Some storage scopes are balky or tricky to apply, but it’s often worthwhile to expend the effort to learn how to use them. Digital-storage oscilloscopes (DSOs) let you do the same type of triggering and event storage as do the analog type, and some can display events that precede the trigger. They are sampled-data systems, however, so you must be sure to apply them correctly (Ref. 1). Once you learn how to use them, though, you’ll appreciate the special features they offer, such as bright CRT displays, automatic pulse-parameter measurements, and the ability to obtain plots of waveforms.
• A digital voltmeter (DVM). Choose one with at least five digits of resolution, such as the HP3455, the HP3456, the Fluke 8810A, or the Fluke 8842A. Be sure you can
  lock out the auto-range feature, so that the unit can achieve its highest accuracy and speed. Otherwise, you’ll be wasting time while the DVM autoranges. For many analog circuits, it’s important to have a high-impedance (>>10,000 MO ) input that stays at high impedance up to 15 or 20 V; the four DVMs mentioned above have this feature. There are many other fine DVMs that have 10 MR inputs above 2 or 3 V and, if a 10 MO input impedance is not a problem, they are acceptable. The most important reason to use a high-input-impedance DVM is because sometimes it’s necessary to put 33 KO or 100 KO resistors in series with the probe, right near the circuit-under-test, to prevent the DVM’s input capacitance from causing the circuit to oscillate. If you’re using a DVM with a 10 MO input impedance and you have a 100 KO resistor in series with the probe, the DVM’s measurements would lose 1 % of their accuracy.
  Auxiliary meters.
• A general-purpose function generator.
• Power supplies with stable outputs.
• A few RC substitution boxes
• An isolation transformer.
• A variable autotransformer,
• A curve tracer.
• Spare repair parts for the circuit-under-test. You should have these parts readily
• available, so you can swap components to make sure they still work correctly.
• A complete supply of resistors and capacitors
• Schematic diagrams.