A customer approached us for assistance with their soundbar, which was producing a loud humming noise upon powering on. Despite this issue, other functions such as Bluetooth connectivity and HDMI input detection were working correctly, suggesting the fault was likely confined to the audio circuit.
After receiving the soundbar, we opened it for inspection. No visible signs of damage or burnt components were found.
To further investigate, we powered it on and used a thermal camera to identify components generating excessive heat—a common indicator of failure. One of the pre-amplifier chips was observed heating up significantly, prompting us to remove the circuit board for closer examination.
Using a microscope, we measured the resistance on the power rail supplying the pre-amplifiers and found it unusually low (~30 ohms). Suspecting the pre-amplifier chip, we desoldered it, but the low resistance persisted. This indicated that the chip itself was not faulty, leaving us uncertain about the root cause.
To pinpoint the defective component, we employed voltage injection—a technique where low voltage is introduced to circuits with abnormal resistance. Careful application of 0.7V revealed a capacitor heating up abnormally. Capacitors are designed to stabilize power and reduce noise; they should never overheat under normal operation.
The faulty capacitor was located near the pre-amplifier chip and removed. After desoldering it, resistance values returned to normal (in kilo-ohms), and no other components overheated. We reinstalled the pre-amplifier chip and verified all surrounding resistances, confirming that everything was functioning correctly.
The repaired board was reassembled into the soundbar and tested thoroughly. The humming noise was eliminated, and audio output was restored. This repair highlighted how even small components like capacitors can cause significant device failures. Capacitors are particularly prone to defects due to excess heat, mechanical damage (e.g., product drops), or manufacturing flaws that manifest later in their lifecycle.
This case underscores the importance of thorough diagnostics in electronics repair. By systematically testing and isolating components, even complex issues like shorted capacitors can be resolved effectively—restoring functionality to devices that might otherwise be discarded.