Troubleshooting

It took me about half an hour to trace down the cause of receptacles that work whenever they feel like it.  Turns out there was a circuit breaker that had intermittent contact with the Electrical Panel's Bus Bar.

Note the evidence of arc'ing (burnt spot, oxidized aluminum in the top right of the connection).  This is the customer's main neutral connection.  This is the most essential connection in any electrical installation.  If this is weak and failing, weird symptoms can be experienced at best; costly damage to electronics can occur at worst.

This was an odd one - This was found in an upstairs bedroom and the offending dead outlet was in the basement.  Receptacles are wired in a daisy-chain fashion - from one outlet to the next.  The loose wire was sending power down stairs.  Sometimes problems originate in areas other than where symptoms are observed.

And other times, problems are found in the same device box as the symptom.  We can clearly classify this as a smoking gun, caused by incorrectly torqued receptacle terminals.