QUICK REFERENCE
The tables to keep at your bench — print this page
VOLTAGES — THE NUMBERS THAT MATTER
| What | Normal | Notes |
|---|
| Phone battery (full → dead) | 4.20 → 3.70 → 3.40 → <3.0V | <3.0V = boost/activate before normal charging |
| USB charger output | 4.75–5.25V | 9V/12V appear only when the phone negotiates fast charge |
| Laptop adapter | 19–20.5V | Read the label — Dell/HP/Lenovo differ |
| Laptop always-on rails | 3.3V / 5V (ALW) | Present with adapter alone, no power button |
| Laptop main rails | 5V, 3.3V, 1.8V, 1.05V, VDDQ 1.2V | Appear in sequence after power button |
| CPU core (VRM) | ~0.7–1.2V | Last rail to come up before CPU runs |
| Display AVDD (phone) | ~5.5–6.0V | Missing = display PMIC on board |
| Display VCI (phone) | ~3.3V | Interface power |
| Mic bias (phone) | ~1.8–2.8V | During a call/recording |
| Camera analog (VCAM) | ~2.8V | Missing = camera power line fault |
DIODE-MODE VALUES (black probe on GROUND, board OFF)
| Measurement | Healthy | Fault |
|---|
| Any power rail to ground | 300–800 | <100 or beeps = shorted rail |
| Battery connector (both ways) | ~0.4–0.6 one way, higher/OL other | Beeps both ways = short on power rail |
| Diode (any) | 0.4–0.7 one way, OL other | 0.00 both = shorted · OL both = open |
| Small capacitor | Charges briefly → OL | Steady beep = shorted cap |
| Coil / inductor / fuse | Near 0 (beeps) — NORMAL! | Coils and fuses are near-shorts by design |
| MOSFET (drain-source vs gate) | Diode-like one direction | Shorted = reads 0 both ways |
RESISTANCE VALUES — COMPONENTS
| Component | Normal reading | Fault |
|---|
| Speaker / ringer | 8 / 16 / 32 Ω | OL = dead coil |
| Vibration motor | 10–30 Ω | OL = dead |
| Earpiece | 8–32 Ω | OL = dead |
| Resistor | Its marked value ±5% | OL = cracked |
| NTC thermistor | Changes with temperature | Open = charging/thermal faults |
| Microphone | Don't measure resistance — check bias voltage (~2V) | 0V bias = line/power fault |
HOT AIR CHEAT SHEET
| Task | °C | Air |
|---|
| Dry washed board | 80–100 | High |
| Small SMD removal | 320–350 | Low-med |
| Shield removal | 350–380 | Med |
| IC removal | 350–400 | Med |
| BGA reballing | 380 | Low |
THE FOUR CURRENT PATTERNS (dead phone on PSU)
| Pattern | Meaning | Action |
|---|
| 0.000A | Input path dead | Trace port → fuse → charging line |
| Steady small, no change on power press | Power-on circuit / EC | Button, flex, board signal |
| Instant max (jumps to limit) | SHORT | Short-killer + freeze spray → remove culprit |
| Steps climbing, settling | Booting normally | Problem is display/software — not power |
BARRAKPORE MARKET GUIDE
| Brands you'll see most | Xiaomi/Redmi · Realme · Samsung A/M series · Vivo Y/V · Oppo · Infinix/Tecno · OnePlus · iPhone (growing) |
|---|
| Most common jobs | Screen replacement · charging port · battery · software/FRP · water damage (monsoon) · dead phones |
|---|
| Known models to learn deeply | Redmi Note series (charging ports) · Vivo Y series (displays) · Samsung A/M (software) |
|---|
REPAIR PRICING GUIDE (labor, Barrakpore 2026)
| Job | Mobile | Laptop |
|---|
| Software fix / OS install | ₹200–300 | ₹300–500 |
| Flash / FRP (with policy) | ₹300–500 | — |
| Screen replacement labor | ₹300–1000 | ₹800–1500 |
| Charging port | ₹300–500 | DC jack ₹500–800 |
| Battery | ₹200–400 | ₹500–800 |
| Water damage treatment | ₹500–1000 | ₹800–1500 |
| Board-level repair | ₹500–1500 | ₹1000–2500 |
| Diagnosis only | ₹100–200 | ₹200–300 (adjusted into repair) |
Parts are always quoted separately. Diagnosis fee adjusts into the repair — customers accept it, and it stops time-wasters.
PARTS SOURCING
| Source | For | Contact |
|---|
| Azad Electronics, Khidirpur | Tools, equipment | +91 7044416312 |
| Khidirpur / Chandni Chowk parts markets | Screens, batteries, flex, ports | Visit per job |
| BGA-221 practice boards | Reballing practice | WhatsApp 9898551166 |
| UMT support / downloads | Flashing software |
The wall cards (write these and stick above the bench):
1. "Beep both ways = SHORT. One way = healthy."
2. "Current limit before connecting. Output off before disconnecting."
3. "Customer devices forbidden until 10 boards."
4. "Test new parts BEFORE fitting."
5. "FRP only with proof of ownership."