Shure it’s a Bad Power Supply

I recently got called out to troubleshoot a commercial audio pa system which I was told had problems with noise in the system. I was following a couple others on this repair (who could not find the problem). These were very nice Shure SLX series systems all tied together with an external power supply-antenna distribution system. Sure (Shure) enough, the system has noise and it seems like standard sort of noise- which I have heard many times, as wireless systems drop in and out of working properly. In an attempt to isolate the problem, I disconnected 2 of the 3 SLX receivers from the power supply and suddenly I smell that dreaded scent of semi-conductors burning up, melting, and becoming unusable. Fear comes over you as you are certain you must have somehow caused this situation. I substituted a common supply into one of the receivers and found it to still turn on and seemingly work.

The question is how does reducing the load on a given power supply cause it to go up in smoke? I don’t know the answer but I think it goes something like this. This power supply had been failing for some time, maybe as much as 2 years as its wireless performance continued to slip away. It seems that a supply running in a balanced end of life situation cannot take any change to the load or it may self-destruct.
Happily I had a 12 volt supply rated almost high enough that I substituted into the main Shure distribution box and everything worked- no more noise in the wireless mics.

I instructed the clients to buy a new Shure power supply for the distribution box. They were very pleased. The moral to the story is: Once a power supply hits 5 years of continuous operation, it may be time to replace it.