Here is tear-down of old Zyxel ES-108 10/100Mbit/s Ethernet switch. I had one on my network for many years, but one day it stopped worked and started making whining noise.
Closer look to details.
The problem seems to the power supply on board putting out wrong voltage to electronics: Varying from around 3.7V to 4V when it should be 3.3V. Chip heats up and nothing works. Maybe not worth to try to fix… get a new faster.