Maharashtra HSC Electronics and Hardware Technician (NSQF E5) cheat sheet

Ohm's law: V = I × R; power P = V × I = I²R = V²/R. Units: volt, ampere, ohm, watt.

Series circuit: R_total = R1 + R2 + ...; current is common, voltage divides in ratio of resistance.

Parallel circuit: 1/R_total = 1/R1 + 1/R2 + ...; voltage is common, current divides inversely with resistance.

Kirchhoff's laws: KCL - algebraic sum of currents at a node is zero; KVL - algebraic sum of voltages around a closed loop is zero.

Capacitive reactance Xc = 1/(2πfC); inductive reactance XL = 2πfL; impedance Z = √(R² + (XL − Xc)²).

Resonance occurs when XL = Xc, i.e. f = 1/(2π√(LC)); at resonance impedance is purely resistive and minimum in series circuits.

AC RMS value = peak/√2 = 0.707 × peak; average value of full sine = 0.637 × peak; frequency f = 1/T.

Transformer turns ratio: Vp/Vs = Np/Ns = Is/Ip; power is approximately constant (ideal transformer).

Resistor colour code: Black 0, Brown 1, Red 2, Orange 3, Yellow 4, Green 5, Blue 6, Violet 7, Grey 8, White 9; Gold ±5%, Silver ±10%.

Silicon diode forward drop ≈ 0.6–0.7 V; germanium ≈ 0.2–0.3 V. Reverse bias below breakdown gives only leakage current.

BJT: NPN conducts when base-emitter is forward biased (VBE ≈ 0.7 V); IC = β × IB; operates in cutoff, active, saturation regions.

MOSFET/IGBT are voltage-controlled; gate is insulated, so gate current is negligible but gate oxide is ESD-sensitive.

Zener diode in reverse breakdown regulates voltage; it must be used with a series current-limiting resistor.

LED needs a series resistor: R = (Vsupply − VLED)/ILED; cathode is the shorter lead / flat side of the body.

Capacitor codes: 104 = 10 × 10⁴ pF = 100 nF = 0.1 µF; 223 = 22 nF. Electrolytic capacitors are polarised - reversed polarity causes failure.

Photodiode, phototransistor, LDR, thermistor and varistor are sensors whose resistance/current changes with light, heat or voltage.

Typical iron tip temperature for Sn63/Pb37 solder is 300–350 °C; for lead-free SAC305 use 350–380 °C.

Good solder joint: shiny, concave fillet, smooth wetting to pad and lead. Cold joint: dull, grainy, ball-shaped, high resistance.

Soldering sequence: clean pad → apply flux → heat pad and lead together → feed solder → remove solder then iron → inspect.

Desoldering methods: solder sucker (manual vacuum), desoldering braid/wick, hot-air rework station, desoldering pump with heated tip.

SMD reflow profile stages: preheat, soak, reflow (peak above liquidus), cooling; excessive peak temperature warps boards and damages parts.

Flux types: rosin (R), rosin mildly activated (RMA), water-soluble (must be washed), no-clean. Flux removes oxide; it is not a cleaning agent for dirt.

ESD-safe soldering: grounded iron tip, wrist strap at 1 MΩ, dissipative mat; never touch IC leads before grounding.

PCB assembly checks: polarity of electrolytics/diodes, IC notch orientation, no solder bridges between adjacent pads, no tombstoned SMD parts.

Number systems: binary base 2, octal base 8, decimal base 10, hexadecimal base 16. 1 hex digit = 4 binary bits.

Boolean identities: A + 0 = A; A·1 = A; A + A' = 1; A·A' = 0; De Morgan: (A·B)' = A' + B'; (A + B)' = A'·B'.

Universal gates NAND and NOR can realise AND, OR, NOT alone; XOR gives 1 only when inputs differ (used in adders/parity).

Half adder: Sum = A ⊕ B, Carry = A·B. Full adder adds carry-in; 4-bit ripple adder chains full adders.

Flip-flops: SR (set/reset, invalid state when both 1), D (data latch), JK (toggles when J = K = 1), T (toggle).

Microcontroller core blocks: CPU, program flash, SRAM, EEPROM, GPIO ports, timers/counters, ADC, UART/SPI/I²C interfaces, interrupt controller.

8051 basics: 8-bit core, 4 KB ROM, 128 B RAM, 32 I/O lines in four ports, two timers, one serial port, 5 interrupt sources; crystal 11.0592 MHz for standard baud rates.

Arduino Uno: ATmega328P, 14 digital I/O (6 PWM), 6 analog inputs, 32 KB flash, 2 KB SRAM; digitalWrite/pinMode/analogRead are standard functions.

Voltmeter connects in parallel with the load; ammeter connects in series. An ideal voltmeter has infinite resistance, an ideal ammeter zero resistance.

Analog multimeter (VOM) reading: select range above expected value, set function, zero the ohms scale by shorting probes before resistance measurement.

Digital multimeter accuracy is quoted as ±(% reading + number of counts); a 3½-digit DMM displays up to 1999 counts.

Cathode-ray oscilloscope controls: time/div sets sweep, volts/div sets vertical scale; period T = (horizontal divisions) × (time/div).

CRO probe compensation is adjusted with a 1 kHz square wave; a 10× probe divides signal by 10 and raises input impedance.

Continuity/diode test: forward drop reads 0.4–0.8 V for a good silicon junction; open circuit reads OL in both directions.

Function generator outputs sine, square and triangle waves; frequency counter measures frequency directly, and LCR meter measures inductance, capacitance and resistance.

Signal tracing method: inject signal at input, follow stage by stage with scope/probe to locate the faulty block; compare against expected waveform.

PC assembly order: install CPU and cooler on motherboard → RAM → motherboard into case with standoffs → PSU → drives → front-panel headers → power and data cables.

SMPS connectors: 24-pin ATX main, 4/8-pin EPS CPU, 6/8-pin PCIe for GPU, SATA power; match keyed connectors, never force.

POST failure diagnosis: beep codes or debug LEDs indicate CPU, DRAM, VGA, BOOT sequence; no display with fans spinning points to RAM or GPU seating.

Troubleshooting rule: verify power (SMPS voltages +3.3, +5, +12 V), then connections, then settings, then components - substitute known-good parts to isolate.

BIOS/UEFI settings: boot order, SATA mode (AHCI/RAID), XMP memory profile, secure boot, virtualisation (VT-x/AMD-V), fan curve.

Device Manager codes: Code 10 (device cannot start), Code 28 (drivers not installed), Code 43 (device reported failure) - reinstall driver, reseat or replace.

Printer/laptop service: check fuser and rollers for paper path jams, clean printhead nozzles, reset waste-ink counter only as per service manual.

Networking hardware: crimp RJ-45 with T568B order (white-orange, orange, white-green, blue, white-blue, green, white-brown, brown); test with LAN tester.

Rectifier circuits: half-wave output frequency = supply frequency; full-wave and bridge = twice supply frequency. Bridge needs four diodes.

Filter capacitor reduces ripple; larger C or larger load resistance lowers ripple. Ripple factor of half-wave ≈ 1.21, full-wave ≈ 0.48 (unfiltered).

Linear regulator (78xx/79xx) needs input at least 2–3 V above output; 7805 gives +5 V, 7905 gives −5 V; add heat sink for high current.

SMPS topologies: buck (step-down), boost (step-up), buck-boost (inverting); efficiency typically 75–95% versus 30–60% for linear regulators.

UPS types: offline/standby switches after mains failure; line-interactive regulates with AVR; online double-conversion gives zero transfer time.

Battery terms: capacity in Ah, C-rate = current/capacity, depth of discharge, cycle life. Li-ion nominal 3.6–3.7 V/cell, lead-acid 2 V/cell, NiMH 1.2 V/cell.

Li-ion charging is CC/CV: constant current to 4.2 V then constant voltage; overcharge or over-discharge protection is done by a BMS.

Inverter VA rating: VA = W/power factor; a 600 VA UPS at 0.6 PF supports about 360 W of load.

ESD control: grounded wrist strap (1 MΩ resistor), conductive/dissipative work mat, grounded iron tip, ionisers in dry areas; store ICs in antistatic tubes or bags.

Human body model thresholds: a person feels discharge near 3 kV, hears it near 5 kV, but CMOS damage can occur below 100 V - invisible failures are common.

Electrical safety: isolate supply and lock off before repair; use one-hand rule on live circuits; RCD/ELCB trips at 30 mA for personnel protection.

Fire class and extinguisher: Class C (electrical) uses CO₂ or dry powder - never water; Class A solid, Class B flammable liquid.

Soldering fume control: use fume extractor or local exhaust; keep flux and IPA away from eyes, use goggles and gloves; ventilate the bench.

First aid for electric shock: switch off supply first, do not touch the casualty until isolated, then call emergency services and begin CPR if trained.

E-waste handling: PCBs, batteries, CFLs and CRTs are hazardous - segregate and route to authorised recyclers under E-Waste Rules; never burn cable or dump in municipal bins.

Lead-free solder and leaded solder waste must not be mixed; wash hands after handling leaded solder and before eating.

Service documentation set: job card/service request, test report, component replacement record, customer handover note with warranty terms.

Schematic reading: identify power rails, signal flow left to right, ground symbols, reference designators (R, C, L, D, Q, U, J, SW, TP).

IPC-A-610 classes: Class 1 general products, Class 2 dedicated service, Class 3 high-reliability; acceptance criteria tighten with class.

QC tools: incoming inspection, first-article inspection, in-circuit/functional test, AOI, visual check under 10× magnifier, statistical process control charts.

Calibration: measuring instruments must be calibrated against traceable standards at defined intervals; record calibration certificate number and due date.

Root cause analysis: 5-Why and fishbone (man, machine, material, method, measurement, environment) to separate symptom from cause.

Customer support flow: log complaint with serial number → reproduce fault → quote → repair → retest → record closure; response time and resolution time are tracked KPIs.

Warranty vs guarantee: warranty covers repair/replacement of defects for a stated period; guarantee is a broader assurance. Document exclusions such as physical or liquid damage.

Business structure options: sole proprietorship, partnership, LLP, private limited company; registration with GST and Udyam (MSME) portal for small service units.

Costing: total cost = fixed cost + variable cost; break-even quantity = fixed cost / (selling price − variable cost per unit).

Working capital cycle for a repair shop: cash → spares inventory → service revenue → receivables → cash; shorter cycle improves liquidity.

GST basics: 18% standard rate on most electronic services; composition scheme for small turnover; invoice must show GSTIN, HSN/SAC code and tax breakup.

Résumé essentials: contact details, skills with proficiency, projects, certifications (NSQF level), education; keep to one or two pages and tailor keywords to the job advert.

Interview preparation: research the employer, prepare STAR (Situation, Task, Action, Result) examples, carry documents, ask about role and training.

Customer service skills: active listening, clear explanation without jargon, written estimate before work, punctuality, follow-up call after delivery.

Record keeping and legal: keep purchase invoices, service records, GST returns and warranty register; maintain price list and transparent payment terms.