Drops output voltage? Drops how far? 10%, 50%, all the way to zero?
How soon does the voltage drop? Within seconds of power up? Within minutes? After several hours?
Check for obviously bad parts, like a diode cracked in half, or a capacitor leaking brown goo out of the top or bottom of it, or capacitors that are running extremely hot when you put your finger on them.
If this power supply is for some proprietary piece of equipment I'd say go ahead and try to fix it, but if its just a generic power supply for a PC I wouldn't waste your time on it and just go buy a new one.
Hi Jim thank for coming back to me . The power supply is for one of my ham radios. It is a mydel mp-30swiv with an out put of 13.8 volts.max current is 30 amp . It can run for days or minutes without any load on it and then just drops off to around 5 volts , so excess heat doesn’t seem to be the cause . I’m only an intermediate ham radio operator so my electronic knowledge is limited . I can only see one rather large capacitor that has a slightly rounded top to it . I’ve looked for dry solder joints but seem unable to find any . Tia rob .
It does sound like old electrolytic capacitors which have lost capacitance.
It is difficult to be specific from a distance.
If an electrolytic capacitor has bulged its end and is leaking, like in the picture by LandonRobinson, then it is definitely faulty and should be replaced.
However it is quite possible for capacitors to have dried out and lost capacitance over the years and still not show any outward signs of distress. In those cases the only thing to do is to measure their capacitance and or their ESR (Equivalent Series Resistance).
If the ESR has gone high then the capacitor will perform badly.
To measure ESR, you need an ESR Meter (obviously!) or you can use an oscilloscope and a function generator.
Look here for good information on this technique:
JimB
Hi Jim
Thanks for the reply .
That was the road I was going to go down . I shall ask the guys in the local club if they have a an esr meter and go from there . Thanks again for your guidance in this matter
Rob
hi ronsimpson
i have looked at the board with a magnifying glass and cant see any .doesn't mean there isn't any though.my first thoughts where with a capacitor problem as Jim has mentioned
thanks Nigel
its certainly a talking point at our local ham radio club.
really just looking for pointers .a new one inst that expensive I'm just curious as to why its failing and if i can trace the fault then its good experience for me
thanks Nigel
its certainly a talking point at our local ham radio club.
really just looking for pointers .a new one inst that expensive I'm just curious as to why its failing and if i can trace the fault then its good experience for me
i've looked but found no schematic. however, since it's a switcher, the first thing to look for is dried out electrolytic caps, as they cause 95% of switching supply failures. they might not be as obvious as the ones pictured above.
i've looked but found no schematic. however, since it's a switcher, the first thing to look for is dried out electrolytic caps, as they cause 95% of switching supply failures. they might not be as obvious as the ones pictured above.