Common smartphone problems and how to diagnose them

Most smartphone faults show up as one of a few symptoms: the phone will not turn on, will not charge, drains too fast, restarts on its own, freezes, has no sound or has been in water. The same symptom can have very different causes, from a dirty charging port to a failed component on the logic board. This guide goes through the most common malfunctions and the checks that help separate a cheap fix from a real hardware fault, both for owners and for technicians at the bench.

Screen faults are a large topic of their own, so we have covered them separately in our article on the five most common smartphone screen problems. Here we focus on everything else.

1. The phone does not turn on

A phone that shows nothing is not necessarily dead. Work through the causes from the simplest to the most expensive:

• Fully discharged battery. Connect a known-good charger and cable and wait 15 to 30 minutes before deciding anything. A deeply discharged battery may not show a charging icon straight away.
• Frozen system. Try a forced restart using the button combination for your model.
• Display fault. If the phone vibrates, rings or connects to a computer but the screen stays black, the problem is probably the display or its connection rather than the phone itself.
• Software failure. A boot loop or a phone stuck on the logo after an update often needs the system to be reinstalled. Back up your data first if the phone can still be reached from a computer.
• Battery or board fault. If none of the above helps, the phone needs a bench diagnosis.

At the bench, a technician powers the board from a regulated power supply instead of the battery and watches the current draw while pressing the power button. A short circuit, no draw at all or a draw that stops at a certain point each point to different areas of the board, which is far faster than replacing parts at random.

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2. The phone does not charge, or charges slowly

This is one of the most frequent complaints, and the charging port is not always to blame. Check in this order:

1. Try a different cable and charger. Damaged cables are the most common cause.
2. Look into the port with a light. Pocket lint packed at the bottom stops the plug from seating fully. Clean it gently with a non-metallic tool only.
3. Check whether the plug wobbles or only charges at a certain angle. That points to a worn or damaged port.
4. Measure what is actually happening with a USB tester between the charger and the phone. If the phone draws almost no current with a good charger and a clean port, the fault is in the port, the charging circuit or the battery.

A USB tester gives you numbers instead of guesses: voltage, current and whether fast charging is negotiated at all. For deeper checks on the board, a multimeter is the next tool; our guide to choosing a multimeter explains what features matter for phone repair.

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3. The battery drains too fast

All lithium-ion batteries lose capacity over time. Apple, for example, states that iPhone 14 and earlier batteries are designed to keep 80% of their original capacity after 500 complete charge cycles under ideal conditions, and iPhone 15 and later after 1000 cycles. Below that level, shorter battery life is normal wear rather than a defect.

Before blaming the battery, check the battery usage screen in settings. One app that keeps running in the background, weak mobile signal or a stuck sync can drain a healthy battery quickly. When battery health is low, replacement is the fix. A swollen battery is different. When the back cover lifts or the screen is pushed out, stop using and charging the phone and have the battery replaced, because a swollen lithium-ion cell is a safety risk.

To slow wear, use the optimised charging or charge limit option if your phone has one, and avoid leaving the phone charging in a hot place.

4. The phone restarts on its own or freezes

Random restarts and freezes are often caused by software, but not always. A useful split:

• Check for an app conflict. On Android, restart in safe mode, which loads the system without downloaded apps. If the problem disappears in safe mode, one of the recently installed apps is the likely cause. Google recommends this exact test for phones that restart, freeze, crash or run slowly.
• Free up storage. A nearly full storage slows the system and can cause crashes. Clearing large media from messengers often helps.
• Install updates. System and app updates fix known bugs.
• Watch for a mechanical pattern. If the phone restarts when you press on the case, twist it or plug in a cable, the cause is likely physical: a worn battery that cannot deliver peak current, a loose connector or board damage after a drop.

A phone that keeps restarting after a full reset, with no apps installed, has a hardware fault.

5. No sound, or the other person cannot hear you

First rule out the simple causes: a Bluetooth headset still connected, Do Not Disturb mode, or a call volume set to minimum. Then check the grilles: earpiece and speaker meshes collect dust and grease, which can muffle sound gradually. If you cannot hear callers but speakerphone works, the earpiece is the suspect. When people cannot hear you, record a voice memo and play it back to test the main microphone, and test video recording to check the second microphone. A dead speaker or microphone after a drop or water exposure usually means a replacement part or a damaged flex cable.

6. The phone has been in water

Water resistance ratings are measured on new phones under controlled lab conditions. Seals wear with age, and many accidents involve salt water, coffee or other liquids. What to do:

1. Turn the phone off and disconnect any cable.
2. Wipe the outside and tap the phone gently with the port facing down to remove excess liquid.
3. Leave it to dry in a dry place with some airflow. Apple advises waiting at least 30 minutes before charging after a liquid alert, and up to a day if the alert comes back.
4. If the phone was in salt water or a sweet drink, or it behaves strangely after drying, take it to a repair shop soon. Corrosion on the board develops over days and weeks.

What not to do: Apple specifically warns against drying a phone with an external heat source or compressed air, pushing cotton swabs or paper towels into the connector, or putting it in a bag of rice, because rice particles can get inside. The rice method is one of several popular misconceptions we covered in 5 phone repair myths.

In the shop, liquid-damaged boards are opened, inspected under magnification and cleaned of corrosion with high-purity isopropyl alcohol before the phone is tested again.

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Quick diagnostic table

If the simple checks do not help, a repair shop with the right test equipment can usually name the faulty part within one visit, and many of these faults end with a single part replacement rather than a new phone.