Source: https://mokxi.com/learn/skillsusa-electronics-technology-practice Updated: 2026-09-27 Learn # SkillsUSA Electronics Technology: circuits to practice before competition Written by the Mokxi team, updated September 27, 2026 Sign up free or see every lesson - 192 parts on the bench - 25 boards running now - 1.00x real time, on every board Click to open it in the editor A series-parallel circuit with one fault. Calculate first, then measure the two joints. SkillsUSA runs an Electronics Technology competition for career and technical education students. The official technical standards, which describe what is tested each year, are published by SkillsUSA for its members. This page does not reproduce them and is not affiliated with SkillsUSA. It is a set of five original practice circuits covering the kinds of skills an electronics technician uses every day, each with questions and answers you can check by measuring. Ask your advisor for the current technical standards and study those first. Then use these circuits to practice the thinking and the meter work, alongside time at a real bench with a real soldering iron. ## Station 1: a transistor as a switch A 2N2222 NPN transistor switches a red LED and a 470 ohm resistor from a 9 V supply. The slide switch puts its 10 k base resistor on 9 V or on ground, and the meter reads collector to emitter. Questions: What is the collector-emitter voltage with the base off? What is it with the base on? About how much base current flows when it is on, and is the transistor saturated? Answers: off, 7.96 V (the LED still drops a little with almost no current); on, 0.04 V; base current about (9 - 0.72) / 10 k = 0.83 mA, and yes, it is saturated, since the collector voltage is nearly zero. ## Station 2: a non-inverting op-amp stage A 10 k over 2.2 k divider puts a DC input on the op-amp’s non-inverting input from a single 9 V supply. The feedback is 22 k from output to the inverting input and 10 k from there to ground. Questions: What is the input voltage? What is the gain? What is the output voltage? Answers: 1.62 V; gain = 1 + 22 k / 10 k = 3.2; output 5.19 V, which is what the meter reads. Change the 22 k to 47 k and the output would try to reach 1.62 x 5.7 = 9.2 V, beyond the 9 V rail, so it clips. Try it. ## Station 3: a 555 on the bench A 555 astable with a scope on the output and the timing capacitor, and a meter averaging the output. Questions: Read the frequency and duty cycle off the scope. Predict them from the resistor and capacitor values first, using f = 1.44 / ((R1 + 2 x R2) x C) and duty = (R1 + R2) / (R1 + 2 x R2). Why does the meter’s DC reading equal roughly the supply times the duty cycle? Answers: the circuit’s own notes give the prediction; the scope and meter confirm it. A DC meter averages the square wave, and the average of a wave that is high for a fraction D of each cycle is D times the high voltage. ## Station 4: logic gates Two buttons drive an AND gate, an XOR gate and a NOT gate, each lighting an LED. Questions: Write the truth table for each gate before you press anything, then check every row. Which gate’s output is on when exactly one button is pressed? Answer: XOR is on when exactly one input is on. AND needs both. NOT is on only when its input is off. ## Station 5: find the fault The schematic says 12 V into R1 (1 k), then R2 and R3 (2.2 k each) in parallel, then R4 (1 k) to ground. One thing on the bench is not as the schematic says. Do not look for it yet. Questions: Calculate what the voltage at the R1-R2-R3 joint and at the top of R4 should be. Then measure both. Which part is at fault, and how do the numbers tell you? Answers: expected 8.13 V and 3.87 V; measured 9.14 V and 2.86 V. Less current is flowing than expected, so the resistance is higher than the schematic says. The numbers match R2 alone in the middle (12 V across 4.2 k gives 2.86 mA), so R3 is open: it has lost its connection at one end. That is how a cold solder joint or a lifted breadboard leg looks from the meter. ## What a simulator cannot practice Soldering, desoldering, reading color bands by eye on a real board, handling parts safely against static, and working to time with real instruments all need a real bench. Use this for the thinking, and spend the rest of your practice with a real iron, safety glasses and good ventilation. ## A troubleshooting routine that works on any circuit Start with power. Measure the supply at the circuit, not at the supply’s terminals, because a bad wire or a blown fuse in between is a common fault. Then check ground the same way. Next, predict before you probe. Work out what a few key points should read, then measure them in order from the supply toward the output. The fault is between the last point that reads right and the first one that reads wrong. On a long chain, measure in the middle first and keep halving the part that is wrong. Only then turn the power off and check suspects with the ohmmeter or continuity range. An open part reads far higher than its value, a short reads near zero, and a part still in the circuit can read low because of what is in parallel with it, so lift one leg if the reading does not make sense. Write down each reading as you go. It keeps you from measuring the same point twice. ## Questions Where are the official SkillsUSA Electronics Technology standards? SkillsUSA publishes its championships technical standards for members. Ask your chapter advisor for the current year’s copy. Is this page affiliated with SkillsUSA? No. It is original practice material. SkillsUSA is named only to say which competition it helps you prepare for. Related ## Keep going How to Use a Multimeter: Practice on a Virtual One TSA Electrical Applications: Practice Circuits Circuit Lab Practice Test: 30 Measured Questions Logic Gates, and the Truth Table You Can Press SkillsUSA technical standards ## Build this for real Open the editor, change a value and watch the number move with it. Nothing to install, and no account needed. Start building Open the editor