Occasionally check the connections between the PSU cables and the miner.  Slow vibration and heat over time can slowly separate the internal metal connections ever so slightly.  This leads to resistance and creates heat (and lead to melting/fire).

Metal corrosion of the internal connections can speed this process as well (another reason why controlling relative humidity is important).  A manufacturer can cheap out on the quality of the internal socket pins and if they use an unplated or thinner variety, they will heat up when heavy current is passing through.