UPMSP High School Mobile-Phone Repair - Code 980 flashcards

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

Ohm's law

Voltage equals current multiplied by resistance (V = I × R). In phone repair it lets you calculate the current through a resistor or the drop across a rail from measured values.

Power formula

Electrical power equals voltage times current (P = V × I), also written I²R or V²/R. It tells you how much heat a component or short will dissipate.

Parallel resistance

For resistors in parallel the reciprocal of the total equals the sum of the reciprocals. Two equal resistors in parallel give exactly half the value of one.

Diode test mode

The multimeter applies a small voltage and shows the forward drop. A silicon junction reads about 0.7 V one way and open circuit the other; a short reads near zero both ways.

PMIC

Power management integrated circuit. It converts battery voltage into the regulated rails that feed the processor, memory, camera and display, and it sequences them at power-on.

eMMC versus UFS

Both are managed flash storage. eMMC is half-duplex with a single lane set; UFS is faster, full-duplex and used in modern mid-range and flagship phones.

MIPI DSI

The high-speed serial interface that carries image data from the processor to the display panel. A damaged DSI lane gives a blank or garbled screen.

Charger IC

The IC that regulates charging current and voltage from USB or wireless input into the battery, and reads the battery thermistor to stop charging when too hot.

Fastboot mode

A bootloader protocol that lets a PC flash partitions over USB. Commands include fastboot devices, fastboot flash and fastboot reboot; it works before Android starts.

Factory Reset Protection

FRP locks a reset phone to the last signed-in Google account. It is removed only by entering that account or through an authorised vendor unlock.

ADB logcat

An Android debug command that streams system and application logs to a PC. It shows crash stack traces and repeating errors that identify a faulty app or service.

Bootloader unlock

Removing the bootloader restriction so custom images can be flashed. On most brands it voids warranty and trips a hardware fuse that cannot be reversed.

Voltage injection

A diagnosis method that feeds a current-limited supply into a shorted rail and finds the component that warms up. Keep the limit low to avoid burning traces.

Current-draw signature

The current a phone takes on a DC supply at power-on. Near zero means an open path, a few milliamps means a standby fault, and over half an amp with heat means a short.

Thermal camera diagnosis

An infrared camera reveals hot spots on a powered board within seconds. It quickly locates a shorted capacitor or failed IC without probing every rail.

Cold solder joint

A dull, grainy joint with poor wetting and high resistance. It causes intermittent faults and is repaired by adding flux and reflowing, not by piling on solder.

BGA reballing

Replacing the solder spheres on a ball-grid-array chip before refitting it. Reusing a chip without reballing causes bridges and cold joints under the package.

Hot-air rework

Removing or refitting SMD parts with heated air, typically 300–380 °C with low flow. The board is preheated first and the part is lifted only when the solder is liquid.

Solder wick

Fluxed braided copper used to remove excess solder and bridges. It is pressed onto the joint with a hot iron and lifted when the braid turns silver.

IMEI structure

A 15-digit device identity: 8-digit type allocation code, 6-digit serial number and 1 Luhn check digit. Changing or cloning it is illegal in most countries.

IMSI

The subscriber identity stored on the SIM. The network uses it to authenticate and route calls; it is separate from the phone's IMEI.

VoLTE

Voice over LTE, which carries calls as IP packets on the LTE network. Without it a phone falls back to 2G or 3G, which are being shut down in many countries.

Nano SIM

The current smallest plastic SIM format, 12.3 by 8.8 millimetres. Older micro and standard SIMs need an adapter, which can jam the reader.

Li-ion charging profile

Constant current until about 4.2 V, then constant voltage with falling current. Charging stops when current drops to a small fraction of the rated value.

ESD wrist strap

A strap worn on the wrist and connected to earth through a one-megaohm resistor. It bleeds static charge safely without exposing the technician to shock.

Thermal runaway

A self-heating failure in a lithium cell where rising temperature increases reaction rate. It is triggered by overcharge, puncture or crush and cannot be stopped once started.

Current-limited supply

A bench DC supply that caps output current. It protects a board under test so a shorted rail does not burn traces or start a fire.

Continuity mode

A multimeter setting that beeps when resistance is below a threshold. It confirms a track or joint is connected but does not prove the resistance is low enough for power.

Job card

A per-device record of model, IMEI, reported fault, parts used, technician and date. It is the evidence used in warranty claims and customer disputes.

Written estimate

A signed document listing fault, parts, labour, warranty and completion date before work starts. It protects the shop from a customer refusing the agreed price.

Break-even repairs

Fixed monthly costs divided by the margin per repair (price minus part cost). It gives the number of repairs the shop must complete each month to cover costs.

Practical exam routine

Safety check, tool check, fault confirmation, repair, functional test and documentation. Each step carries marks, so skipping documentation loses points even if the repair works.