Quote:
|
Volenti, how come 90% of failed psu's we get at work have blown those two big black caps?
|
Really? like exploded? or simply failed? Most of the powersupplies that I've seen dead (including ones that have died on me) have had the mosfet timing circuit fail, causing 2 banks of mosfets to turn on at the same time = magic smoke. Some of the supplies will simply blow the internal fuse but the symptoms are usually terminal anyway.
Hmm, the only 2 things that I can think of that would cause an electrolytic cap to explode are exessive heat (naked flame on the case of the cap, don't ask how I know this
) or overvoltage, it's highly unlikley that a sufficient spike could get through both filters (one on the powersupply board, usually another on a small seperate board attached to the inside of the powersupply case at the mains treminals) to cause the caps to rupture, certainlly in 90% of cases.
Unless the specific caps being used don't have a very large safety margin between their rated and operating voltage, and mains voltage surges(which the filters won't have any effect on, unless you use a UPS) are pushing the caps over edge...
Electrolytic caps can dry out over time and have less storage potential, but that's normally 5-10year process.
I live in australia and we use 50hz 240v mains, and the powersupplies are slightly different to accomadate this, but the overall design principle should be the same...