UPMSP Vocational Mobile Repairing key terms

The relationship stating that voltage equals current multiplied by resistance (V = I × R). Technicians use it to calculate expected voltage drops, current draw, and resistor values when tracing faults in a phone circuit.

A measuring instrument that reads voltage, current, resistance, and continuity. In mobile repair it verifies rail voltages, checks fuses and tracks for continuity, and confirms whether a component is open or shorted.

A check that confirms an uninterrupted conductive path between two points, usually signalled by a beep. It is used to verify tracks, connectors, and filter components before assuming an IC is faulty.

An unintended low-resistance path that lets excessive current flow. On a phone PCB it typically causes high current draw, heat, or a dead device, and is located by voltage injection or thermal inspection.

A bench instrument that provides a stable, adjustable voltage and shows current consumption. Repairers use it instead of a battery to observe boot current patterns and to inject voltage when hunting shorts.

A passive component that stores and releases electrical energy and blocks direct current while passing alternating signals. In phones it mainly filters supply rails and couples signals; a leaky or shorted one can kill a power rail.

A passive component that limits current and divides voltage according to a fixed value. Phone boards use tiny surface-mount resistors as pull-ups, sense elements, and signal terminators.

A named supply line, such as the main battery rail or a regulated low-voltage rail, that feeds a group of circuits. Measuring a rail's voltage and resistance tells you whether its regulator or a load is faulty.

Power management integrated circuit: the chip that converts battery voltage into the many regulated rails the phone needs and controls charging and sequencing. A failed PMIC often causes no-boot or no-charge symptoms.

The central processor, usually combined with graphics, modem, and other blocks on one system-on-chip die. It executes firmware and coordinates peripherals, so a faulty SoC commonly produces dead or looping boot behaviour.

The embedded storage standards used for a phone's internal memory. eMMC is the older parallel-free design and UFS is faster; both hold firmware and user data and can fail with corruption or read errors.

A drawing that shows components and their electrical connections by symbol rather than physical position. It is the primary reference for tracing a signal or rail from connector to chip during diagnosis.

Software that displays a PCB layout with component positions and net connections, often linked to a schematic. It helps locate a test point or component on a densely populated board without guessing.

Electrostatic discharge: a sudden transfer of static charge between bodies. It can destroy or weaken sensitive chips invisibly, so grounded mats, wrist straps, and antistatic packaging are mandatory at the bench.

A band worn on the wrist and connected through a resistor to a grounded point, slowly bleeding static charge away from the body. It protects boards during handling and soldering work.

A conductive or dissipative work surface that is connected to earth and prevents charge build-up on boards, tools, and parts placed on it. It forms the base of a safe repair bench.

A tool that delivers temperature-controlled air from a nozzle to melt solder on surface-mount parts. It is used to remove and refit ICs, shields, and connectors, with flux and careful airflow to avoid displacing nearby parts.

Heating a joint or component until the solder melts and wets properly, then letting it cool to form a sound connection. Correct reflow avoids cold joints and prevents damage from excessive heat or movement during cooling.

A chemical agent applied during soldering that removes oxides and improves wetting. It helps solder flow evenly, reduces bridges, and must be cleaned afterwards when it is the corrosive type.

An unintended blob of solder joining two adjacent pads or pins. It creates a short that can stop a phone booting or damage a rail, and is removed with flux, wick, and a clean iron tip.

A braided copper strip that absorbs molten solder when heated against a joint. It is used to clean pads, remove excess solder, and clear bridges without damaging the board surface.

A dull, grainy solder connection caused by insufficient heat, dirty surfaces, or movement during cooling. It gives poor electrical contact and intermittent faults, so it must be reflowed with fresh flux.

A heated plate or infrared unit placed under the board to raise its overall temperature before hot-air work. It reduces thermal stress, helps large boards reflow evenly, and lowers the air temperature needed.

A thin insulated wire soldered between two points to restore a broken track or bypass a damaged section. It must follow the correct net and be secured so it does not short against shields.

The sequence of current values a board draws from a DC supply when the power button is pressed. Reading it, from standby to boot peaks, tells an experienced technician whether the fault lies in power, storage, or the CPU.

The low-level software stored in the phone's memory that starts hardware and runs the operating system. Corruption or mismatch between firmware and hardware causes boot loops, missing features, or a dead device.

Writing a firmware image to the phone's storage through a service tool or recovery mode. It is used to repair software faults, but correct model and region files are essential to avoid bricking the device.

The first program that runs after power-on, initialising hardware and loading the operating system. An unlocked or corrupted bootloader affects flashing options and can leave the phone stuck at the logo.

A phone that no longer boots or responds because of failed firmware, a bad flash, or hardware damage. Recovery depends on whether the bootloader or a low-level service mode is still reachable.

The baseband processor handles cellular radio communication, and the IMEI is its unique identity number. Missing baseband or a null IMEI means no network service and points to firmware or radio-section faults.

A measure of received radio power, shown in bars or decibels referenced to a milliwatt. Comparing it against a known-good phone helps separate antenna and RF faults from network or SIM problems.

The conductive parts and flex cables that radiate and receive cellular, Wi-Fi, and GPS signals. Poor contact, corrosion, or a damaged flex causes weak signal and dropped calls even when the radio chip is fine.

A tiny push-on or snap connector that carries radio frequency signals between the main board and antenna flex. It must seat fully; a loose or damaged one causes weak or absent signal.

The chip that regulates current from the charger into the battery and reports charging status. A faulty unit causes slow, absent, or false charging and may also prevent the phone from powering on.

An electronic board inside the battery pack that prevents overcharge, over-discharge, and short-circuit current. If it trips or fails, the pack may show no voltage at its terminals even when cells are charged.

The number of full charge and discharge cycles a battery has completed, reported by the phone's fuel gauge. A high count with reduced capacity indicates normal ageing and justifies replacement.

The duty to protect a customer's photos, messages, accounts, and passwords during repair. Technicians should ask consent before wiping a device, avoid unnecessary access, and never copy or share personal data.

A written record of the device, reported fault, agreed work, price, and customer signature. It protects both shop and customer if a dispute arises and supports clear communication about warranty terms.

The stated terms covering how long a repair or part is guaranteed and what is excluded, such as liquid damage or physical breakage. Explaining it before work begins prevents later disagreement.

Copying a customer's files and settings to another location before risky work such as flashing or board-level repair. It should be offered and documented, since some procedures can erase all user data.