What is the usual reason that low power domestic, offline SMPS's fail?

[treez]

Hello,
Regarding offline, domestic , SMPS's of about 15-30W power, what is the usual reason for them to fail?
Also, can they be repaired?

Is the main failure mechanism the occasional 1KV line transients that eventually blow out the MOV, and then blow out the circuitry that was protected by the MOV?

Or is the main failure mechanism the drying out of the electrolytic capacitors, which overheat due to their increased ESR when they're dried out?.

I am just wondering, if the problem is overheating, then it may be an idea to put in a temperature monitor and shut the thing down when it overheats, then it can be repaired by replacing the electrolytics, and then sent back into service?

 

[schmitt trigger]

I haven't seen domestic made low power supplies in a loooong time. By domestic, meaning any country in the world except China.

I did however, a study of CFL failures (all Chinese made) over several years. The largest failure mechanism, was the preheat filaments going open, followed by switching transistor failure.

 

[treez]

the switching transistor failure I agree, comes up time and again, the problem is, did it just happen, or was it due to some other component such as a cap going short, and then transistor fails due to the s/c current.

 

[schmitt trigger]

In my particular study, no other component had failed.
It wasn't a line transient either. The light fixture had 10 lamps, all wired in parallel. And a single lamp would fail.
Additionally the failure would always occur during startup. One lone exception was a crappy electrolytic cap that exploded during normal operation.