UPMSP Vocational Mobile Repairing flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Ohm's Law

The relationship V = I × R, where V is voltage in volts, I is current in amperes, and R is resistance in ohms. Used to calculate expected current or resistance in a circuit.

Power Formula

Electrical power P = V × I, also written P = I²R or P = V²/R. It tells how much energy per second a component dissipates, which helps spot overloaded parts.

Diode Mode Test

A multimeter function that applies a small forward voltage and displays the drop. A silicon junction reads about 0.6–0.7 V; near-zero indicates a short, OL indicates an open.

Parallel Resistance

For resistors in parallel, 1/R = 1/R1 + 1/R2 + ... The equivalent resistance is always lower than the smallest individual resistor. Two equal resistors give half the value.

PMIC

Power Management Integrated Circuit. It converts battery voltage into the multiple regulated rails (buck and LDO outputs) that supply the SoC, memory, display, and radio sections of a phone.

eMMC and UFS

Embedded flash storage standards used for phone firmware and user data. eMMC is the older standard; UFS is faster and used in modern devices. Both can fail as hardware or as corrupted partitions.

RF Front-End Module

The block between the antenna and the transceiver, containing switches, filters, and often the power amplifier. It routes the correct band to the radio and is a common cause of single-band signal faults.

Board-to-Board Connector

A multi-pin connector joining two PCBs or a board to a flex. Bent or corroded pins cause no-display, no-charge, or no-boot symptoms depending on which pin group is damaged.

Screw Mapping

The practice of recording each screw's position during disassembly. Screws vary in length, and a long screw in a short hole can puncture the board or battery.

Adhesive Softening

Heating the frame to roughly 60–80 °C softens the adhesive holding the display or back cover. Excessive heat damages OLED panels and lithium cells, so temperature must be controlled.

Battery Connector First

A disassembly rule: disconnect the battery connector before handling other connectors, and reconnect it last. This prevents short circuits while flexes and boards are moved.

Current Draw Signature

The pattern of current a board draws from a DC supply. Near-zero suggests an open circuit, high steady current a short, and pulsing current a boot loop. Compare with a known-good board.

Thermal Fault Location

Using a thermal camera or isopropyl alcohol evaporation to find a shorted component. The warm part, or the spot where alcohol dries fastest, is the likely fault.

Substitution Testing

Swapping a suspected part for a known-good one, such as a battery, screen, or flex, to quickly decide whether the fault lies in the device or the accessory.

Cold Solder Joint

A dull, ball-shaped joint that did not wet properly, usually from insufficient heat or flux. It causes intermittent connections and must be reflowed with fresh flux.

Reflow Temperature

The peak temperature a board or component can withstand during soldering. Lead-free SAC305 melts near 217–220 °C; exceeding a datasheet limit deforms connectors and damages parts.

Hot Air Rework

A technique using heated airflow to melt solder around a component. Preheat the board, direct airflow around the part, and lift only after the solder is fully liquid.

BGA Reballing

Replacing the solder balls under a ball-grid-array package using a stencil, correct-diameter balls, flux, and a reflow profile. Misalignment causes hidden bridges under the package.

EDL Mode

Emergency Download mode on Qualcomm chipsets. It allows low-level flashing through a signed programmer and Firehose loader, and is used to recover devices that will not boot normally.

Fastboot

A bootloader protocol used to flash partitions, unlock bootloaders, and recover devices. It requires the correct image for the exact model and build; a mismatch can brick the phone.

Firmware Mismatch

Flashing an image built for a different model or region. Symptoms include boot loops, missing baseband, and failed network registration, and recovery usually needs a full correct flash.

Signal Strength dBm

A logarithmic measure of received power. Values closer to zero are stronger: about −50 to −70 dBm is excellent, −90 to −100 dBm weak, and below −110 dBm marginal.

SINR

Signal-to-Interference-plus-Noise Ratio. It measures signal quality rather than raw strength; high strength with poor SINR usually indicates interference rather than distance from the tower.

APN Settings

Access Point Name configuration that tells the phone how to reach the carrier's data network. A wrong APN typically allows voice calls but blocks mobile data.

Li-ion Voltage Range

A lithium-ion cell is nominally about 3.7 V, fully charged at about 4.2 V, and cut off near 3.0 V. Operating outside this range damages the cell or triggers protection.

CC/CV Charging

The standard lithium charging profile: constant current until the cell reaches its full voltage, then constant voltage with tapering current until charge completes.

Swollen Battery

A lithium cell that has expanded due to gas buildup, often from age, heat, or overcharge. It must never be charged or punctured; isolate it and dispose through e-waste channels.

ESD Wrist Strap

A conductive strap worn on the wrist and connected to ground through a resistor. It safely bleeds static charge from the technician, protecting sensitive components from electrostatic discharge damage.

Anti-Static Packaging

Bags or foam that prevent static buildup around sensitive parts. Plain plastic bags generate and hold charge, so boards and ICs must never be stored in them.

Lithium Fire Response

Burning lithium cells require a lithium-rated or Class D extinguisher. Water can worsen or spread the reaction, and the cell should be isolated and allowed to cool under supervision.

Repair Job Sheet

A written record of device condition, reported fault, agreed price, and customer signature. It protects both shop and customer and documents warranty terms.

Warranty Terms

A written statement of warranty duration, what is covered (parts versus labor), and exclusions such as water or physical damage. Clear terms reduce disputes and build trust.