I accidentally left an Arduino connected to a second power source while plugging it into my Dell E5470 laptop over USB. I later realized the external source was 9V AC. The Arduino now appears to be dead, and the laptop screen went black around the same time, although that may have just been power saving. Since then, the laptop has had trouble waking from standby: after waiting a few minutes, I sometimes have to press the power button to put it back into standby before it will start normally. The USB port involved still appears to work. What safe tests can I perform to check for hardware damage? Would checking the port's voltage with a USB tester or reviewing Windows Event Viewer be useful?
3 Answers
Start with a complete shutdown, disconnect the charger and all USB devices, then power it back on. If the standby problem continues, back up your data and have the laptop inspected. A USB port working normally does not prove that its protection circuitry or the motherboard was unharmed. Avoid repeatedly experimenting with the port or connecting expensive devices.
The Arduino’s USB connection could potentially have fed an incorrect voltage back into the laptop, depending on the board and wiring. The amount of current available does not automatically make 9 V AC safe; sensitive USB and motherboard components can be damaged even briefly. Since the laptop is now behaving oddly during standby, professional diagnostics would be more useful than software logs alone.
A USB tester can confirm that the port is producing roughly its expected 5 V, but that only checks basic output voltage and is not a complete hardware test. Measuring current or trying to force a load can create more risk. Windows Event Viewer may show crashes or power-management errors, but it cannot reliably detect electrical damage.
The fact that the port still charges or recognizes a device only shows that some of its functions survived. It does not rule out intermittent or power-management damage elsewhere on the system.