Safety in Mobile Phone Repair
The Safety domain checks whether you can protect yourself, the customer's phone and the shop while handling mains-powered equipment and lithium-ion batteries. Questions combine hazard recognition with the correct first response, so learn the reason behind each rule.
Mains and battery hazards
- India's wall supply is 230 V AC, 50 Hz. Unplug a charger before opening it; a multimeter on a resistance range connected to live mains can arc and be destroyed.
- A phone battery is only 3.7-4.2 V but can deliver tens of amps through a short. Never rest metal tweezers or a metal spudger across battery contacts.
- A swollen battery has generated gas from cell degradation. Do not charge, puncture or bend it; remove it with plastic tools and isolate it.
ESD and fumes
- CMOS ICs are damaged by static far below what you can feel, so wear a 1 MΩ wrist strap on an earthed mat and avoid synthetic clothing on a dry day.
- Solder and flux fumes need extraction. Wear safety glasses when clipping leads, keep IPA away from flames, and wash hands after handling leaded solder.
Fire response
- Isolate power first. Use CO2 or dry powder on electrical fires; place a burning cell in a metal container with dry sand and move it outdoors.
Worked example
A customer hands over a phone whose back cover is lifting. You power it off, do not plug in a charger, open it on a non-flammable mat, lift the battery with a plastic card, and drop it into a metal tin of sand. Reasoning: the bulge is gas from a failing cell, and any puncture or charge current can start thermal runaway. The phone is booked for a battery replacement and the old cell goes to e-waste.
Traps that cost marks
- Believing rubber gloves make mains work safe; they do not.
- Testing a suspect battery by charging it just to see.
- Throwing a lithium cell in ordinary rubbish.
- Ignoring a swollen battery because the phone still switches on.