Phone Charges at 0.05 A After a USB-C Port Replacement
A customer brings in a three-year-old Android phone that stopped charging. Another shop replaced the USB-C port. Now the phone shows a charging icon only when the cable is wiggled, the battery level stays at 2%, and a USB power meter shows 5.1 V at 0.05 A, occasionally jumping to 0.45 A at 5.0 V. The charging IC area reaches 48 °C in 30 seconds, while the rest of the board is at 30 °C. The battery measures 3.42 V open-circuit; with a 1 A load it drops to 3.05 V. With the battery disconnected and a bench supply set to 4.2 V, the phone draws 40 mA in boot mode. The customer wants a 'software reset' because data is not backed up and refuses to leave the phone for a board-level repair.
1. Interpret the current draw, thermal reading and battery measurements. What faults are possible, and which is least likely?
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0.05 A at 5.1 V means the phone is drawing 0.25 W, far too little to charge; the occasional 0.45 A step is about 2.3 W, still low for a smartphone. The 48 °C hot spot at the charging IC in 30 seconds indicates local power dissipation, likely a partial short, a damaged IC, or a miswired port causing a protection circuit to cycle. The battery open-circuit voltage of 3.42 V is low but not zero; dropping to 3.05 V under a 1 A load shows very high internal resistance, so the battery is aged or damaged and may not accept charge. The 40 mA draw in boot mode with a 4.2 V bench supply suggests the phone can boot but is not necessarily healthy. The wiggling sensitivity points to the replaced port or its solder joints.
Three faults may coexist: port, battery and charging IC. A software reset is least likely because software cannot explain a 48 °C hot spot or a battery that collapses under load.
2. Outline a safe diagnostic and repair sequence that protects the customer's data.
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First, inspect the USB-C port under magnification and check for bent pins, bridged pads and cracked solder joints; wiggle the cable while monitoring VBUS and CC resistance. Power the board from a current-limited bench supply at 4.2 V with the battery disconnected and measure boot current. If the board draws 40 mA and boots, back up the data before any further work, using a known-good battery or bench supply. Then test the battery with a proper charger/analyzer; do not fast-charge a battery that drops to 3.05 V under 1 A.
Measure the charging IC input and output rails and check for a short on the output. Use thermal imaging or isopropyl alcohol to locate the hot component. Replace the port only after confirming its pinout, and replace the battery with the correct type. Do not bypass the protection circuit or apply 5 V directly to the battery terminals.
3. The customer refuses board-level repair and demands only a software reset. Write the advice you would give.
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Tell the customer honestly that a software reset will not repair a hardware short or a worn battery, and that continuing to charge a faulty battery creates a fire risk. Because the data is not backed up, the safest plan is to stabilise the phone on a bench supply or a known-good battery, attempt a data backup before board-level repair, and only then replace the port, battery or charging IC. Warn that board-level repair can occasionally worsen the fault, so the backup should come first.
Offer a written estimate with the options: data recovery only, repair with a guarantee, or replacement. If the customer refuses repair, return the phone with the fault documented and advise against charging it unattended. Do not promise that data will be preserved.