Tristar Stuck Relay or Transformer Hum

Coffee maker emits unusual buzzing or humming even when not brewing.

This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.

If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.

Possible Causes

Relay on PCB stuck energized, Vibrating low-voltage transformer, Loose PCB mounting, Electrical resonance in power supply

Safety first: Unplug the unit if noise is continuous when idle.

Observe behavior: Plug in and listen. If the noise starts immediately and persists, a component on the PCB is likely vibrating.
Internal inspection (advanced): Remove the bottom cover and gently press on the transformer or relays with an insulated tool (while unplugged) to see if they are loose. Tighten mounting screws.

Note: Persistent humming may indicate a failing transformer or relay; replacement of the PCB or component is recommended.

Hard 4/5

Main Control PCB (Transformer/Relays)

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