Pocket Reference Cards
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Diode-test signaturesDMM
| Silicon (rectifier / signal) | 0.5–0.7 V | OL | Healthy |
| Schottky | 0.15–0.45 V | OL | Healthy — low forward is normal, not a defect |
| Germanium (old equipment) | 0.2–0.3 V | OL | Healthy |
| LED | 1.6–3.3 V (lights faintly) | OL | Healthy — blue/white may exceed some meters' test voltage |
| Zener (forward) | 0.5–0.7 V like silicon | OL | Forward only — reverse breakdown needs applied voltage above its rating to verify |
| Any junction | low (≈0 V) | low (≈0 V) | Shorted — lift one leg to rule out a parallel path |
| Any junction | OL | OL | Open / dead |
Logic-level thresholdsLOGIC
| TTL | 5 V | 0.8 V | 2.0 V |
| LVTTL | 3.3 V | 0.8 V | 2.0 V |
| 5 V CMOS (HC etc.) | 5 V | ~1.5 V (0.3×Vdd) | ~3.5 V (0.7×Vdd) |
| 3.3 V LVCMOS | 3.3 V | 0.8 V | 2.0 V |
| Lower core rails | 2.5 / 1.8 / 1.2 V | proportional to Vdd | proportional to Vdd |
Resistor color codeR
| Black | 0 | ×1 | — |
| Brown | 1 | ×10 | ±1% |
| Red | 2 | ×100 | ±2% |
| Orange | 3 | ×1 k | — |
| Yellow | 4 | ×10 k | — |
| Green | 5 | ×100 k | ±0.5% |
| Blue | 6 | ×1 M | ±0.25% |
| Violet | 7 | ×10 M | ±0.1% |
| Gray | 8 | — | — |
| White | 9 | — | — |
| Gold | — | ×0.1 | ±5% |
| Silver | — | ×0.01 | ±10% |
SMD resistor codesSMD
| 3-digit | 472 | 47 × 10² | 4.7 kΩ |
| 3-digit | 100 | 10 × 10⁰ | 10 Ω |
| 4-digit (1%) | 4702 | 470 × 10² | 47 kΩ |
| R-notation | R10 | decimal point at R | 0.10 Ω |
| R-notation | 4R7 | decimal point at R | 4.7 Ω |
| Zero-ohm jumper | 0 or 000 | — | 0 Ω (link) |
Polarity marks±
| Aluminum electrolytic | Stripe on can | NEGATIVE lead |
| Tantalum | Stripe / bar | POSITIVE lead ⚠ opposite of electrolytic |
| Diode | Band | Cathode |
| LED | Flat side / shorter lead | Cathode |
| DIP / SOIC / QFP | Dot or notch | Pin 1 |
| BGA | Corner mark | Ball A1 |
Reference designatorsREF
| R | Resistor |
| RV / VR | Variable resistor / potentiometer (VR also used for voltage regulator on some schematics — confirm from the part) |
| C | Capacitor |
| L | Inductor / coil |
| FB | Ferrite bead |
| D / CR | Diode (CR common on aerospace & mil schematics) |
| Q | Transistor (BJT / MOSFET) |
| U | Integrated circuit |
| Y | Crystal / oscillator |
| F | Fuse |
| K | Relay |
| T | Transformer |
| J | Jack / connector (fixed half) |
| P | Plug / connector (mating half) |
| S | Switch |
| BT | Battery |
| TP | Test point |