[sdiy] [AH] Arp Solina with excessive chorus noise

[Richie Burnett]

Yes, electrolytics in SMPSUs have a hard life!  Even if they are sized 
correctly to minimise heating due to their own high current-ripple, they're 
often sandwiched tightly in between transformers, chokes and heatsinks that 
indirectly heat them, speeding up the drying-out process!  Once the ESR 
starts to rise, it's a runaway process because the same ripple current now 
causes even more heating.  The capacitor is only heading in one direction 
from this point.  Interestingly electrolytic capacitor ESR is actually at 
it's maximum at low temperature, but it's running for long periods at high 
temperature that degrades it.  So SMPSUs with knackered electrolytics often 
continue to work fine until there is a power outage or the equipment is 
turned off one day.  Then once they cool down, the ESR increases massively 
(particularly if it's winter and ambient temperature is cold), and the power 
supply is unable to start up again with this amount of series resistance. 
This is a very typical failure mode for Sky boxes and IT equipment.  It's 
also responsible for many of the road signs, shop signs, street-lights etc, 
with LED illumination that blink pitifully every second or so.

-Richie,

> Electrolytics in SMPSUs do indeed degrade quicker. It is the same
effect, but the large, high-frequency ripple currents to which they are
exposed causes internal heating which hastens the process. It's also
fair to say that many SMPSUs do not have the same design margins as
equipment of old.