According to the problem analysis result done by TSA, you can directly begin the subsequent troubleshooting process from the corresponding potential root cause.

5-4-1-1 - Use a multimeter to measure the volts from the power inlet & outlet of the 5v transformer.

• Result 1 - Both 24v DC inlet and 5v DC outlet are identified.
  Start 5-4-1-2.
  
  
• Result 2 - 24v DC inlet is identified, but 5v DC outlet is not identified. 
  Start 5-4-1-3.

• Result 3 - Both 24v DC inlet and 5v DC outlet are not identified.
  Start 5-4-1-4.

5-4-1-2 - Reconnect the 5v DC outlet wire and verify the fridge interlock functionality.

• Result 1 -The fridge interlock is restored to regular operation.
  Issue closed. (Root cause: 5v DC outlet wire disconnected.) 
  
  
• Result 2 - The fridge interlock is still malfunctioning. 
  Escalate to TSA for machine swap.

5-4-1-3 - Replace the 5c DC transformer and verify the fridge interlock functionality. 

• Result 1 -The fridge interlock is restored to regular operation.
  Issue closed. (Root cause: 5v DC transformer malfunction.) 
  
  
• Result 2 - The fridge interlock is still malfunctioning. 
  Restart 5-4-1-1.

5-4-1-4 - Verify 24v DC outlet from the power supply.

• Result 1 - 24v DC outlet is identified.
  Start 5-4-1-5.
  
  
• Result 2 - 24v DC outlet is not identified. 
  Start 5-4-1-6.

5-4-1-5 - Reconnect the 24v DC outlet wire (both the power supply side and the 5v transformer side) and verify the fridge interlock functionality. 

• Result 1 -The fridge interlock is restored to regular operation.
  Issue closed. (Root cause: 24v DC inlet wire disconnected.) 
  
  
• Result 2 - The fridge interlock is still malfunctioning. 
  Restart 5-4-1-1.

5-4-1-6 - Replace the power supply and verify the fridge interlock functionality.

• Result 1 -The fridge interlock is restored to regular operation.
  Issue closed. (Root cause: Power supply malfunction.) 
  
  
• Result 2 - The fridge interlock is still malfunctioning. 
  Restart 5-4-1-1.