Comment by hyperdimension

"common failure mode" = 'they break in a particular way a lot'

As Randy Fromm says, "the things that work the hardest fail the most"

Examples: MLCC (multi-layer ceramic capacitors) over time will often fail short.

Older devices with electrolytic capacitors (the large can-shaped things often situated by where the power input is) have a liquid electrolyte in them that evaporates (boils off?) over time. When it does, they lose their capacitance and the power supply stops being able to supply (good) power.

The point being, when something stops working, check these things first. It's like if your lawnmower dies on you, don't go pulling off the head to look at the piston. Check if there's gas in the tank first.

Finally, a DMM is a digital multimeter. This is your basic tool to measure voltage, current resistance, capacitance, et c.) You can't do much troubleshooting without one.

Hope this helps.