Power Supply Dropping Out

[vln1502]

We run 5V power supplies that are dropping out intermittently. We set V at the power supply to 5.25VDC and try to maintain 4.85VDC at the farthest point (about 8'). The supply is running 5 serial cards and 10 LCD displays. These are in an enclosed cabinet and there is a small cooling fan. The system is about 8-9 years old. My question is: Do power supplies just die of old age? Is there a way to check some of the components?
These seem to work fine if we turn the AC off and then back on, but a few hours later the same thing happens. Thanks, vln1502

 

[jem]

Sounds like it might be thermal shutdown. Is it a linear regulator? It may be that when the ambient gets too high (which causes the internal junctions of the regulator to get even hotter), it's thermal protection kicks in. Turning it off, cools it down a bit, and it runs again for a while. Can you locate the regulator and do a temperature reading on the case? That should tell you.

 

[lavenatti]

Sounds like jem hit the nail on the head.

Try checking the inside of the supply for accumulated dust, check the fan blades also. A larger fan or maybe just a new one may do the trick for you too.

 

[vln1502]

Thanks, jem and lavenatti, we do get some dust build-up but we vacuum a couple times a year. Before we installed the fans we lost caps pretty regularly but not so much since. I'm not sure of the ambient but you both seem pretty sure it's heat related..... maybe I'll punch a few more vent holes down near the p.s.
Thanks