Lots of electronic hardware gets problems its psu and more specificly: with the electrolytic capacitors.
How do old capacitors usually affect the capacitance of that electrolytic capacitor?
What effect does a bad electrolytic capacitor have on the input of the PSU?
What effect will have if the bad capacitor is on the output?
Note: I have measured the voltage several times and it is usualy correct but the electronic equipment only starts after replacing the capacitors.
From my experience in industrial electronics repair: pre 2000 caps used to fail after 10-15 years in service post 2000 caps just start to fail n extreme cases. Most failed capacitors INCREASE capacitance and ESR in initial failure stages, if left long enough they:
a) leak electrolyte out
b) swell
c) become open circuit
d) decrease capacitance
d) all of above
On the input of Switchmode PSU Increased ESR capacitors cause ripple voltage increase and negatively affect transient load regulation, can lead to power transistor failure.
On the output they increase output noise negatively affect transient load regulation.
On the switchmode IC supply they usually cause failure to start - applies only to mains PSU's and DC/DC converters where input voltage is above ~80 V
Electrolytic capacitors are usually specified as "so many" hours at such and such a temperature. From that and the operating environment you can predict how long it takes for the capacitor to have degraded to the limit values specified in the data sheet. So, if the capacitor doesn't have a data sheet that contains this: -
Then they are probably trashy capacitors and should not be used.
The operating hours might be 2,000 h and, quite a few are good for 10,000 h but, 10,000 hours is still only 1.14 years so "what's the trick" you might ask. It's the operating temperature. A capacitor might be rated at 10,000 h at 105 °C but at 95 °C the operating life (or endurance) will be twice as long and, at 85 °C it will be 4 times as long.
$$\boxed{\text{Every 10 °C reduction doubles the endurance period}}$$
Operating at half the rated voltage for its lifetime will also deliver a lifetime extension of 2.
$$\boxed{\text{Halving the applied voltage compared to rated doubles the endurance period}}$$
But electrolytic capacitors will degrade and you have to decide how much your circuit is affected by the degradation and if the circuit can cope with the degradation quoted in the data sheet for the "end of life".
See also this answer for more details.
Second how will affect a bad electrolitic capacitor on the input of the PSU? And how will it affect if the bad capacitor is on the output?
If you can avoid electrolytics then you get a certain improvement but if you design your power supply assuming end-of-life degradation levels then you are also good to go. For an undisclosed generic power supply with no details of its design it's impossible to generalize without doing a full reverse engineering of it.
Underlying the temperature effects on lifetime and failure is ---- the removal of HEAT from INSIDE the capacitor.
The capacitor has only 2 leads. Ensure those 2 leads go directly to WIDE pieces of metal foil. Since usually one of the leads goes to GROUND, you have an excellent opportunity to perform thermal engineering and keep that capacitor much cooler.
Also ensure the ungrounded lead has wide foil, and that foil is immediately passing OVER GROUND, for about a centimeter. A centimeter is a useful distance (in FR-4) to dump heat into an underlying plane. You could include an otherwise useless 1cm by 1cm bulge on the HOT LEAD, right by the lead, to dump heat into the underlying PLANE (Gnd or otherwise).
You might strongly focus on "thermal reliefs" around the lead, if the cap is throughhole mounting. Thermal Reliefs will DOUBLE THE THERMAL RESISTANCE of that region of foil.
Copper foil of standard thickness is 70 ° C per watt per SQUARE OF FOIL. Thus a trace 10mm long and 1mm wide has 700 ° C of thermal resistance.
Its your task to explore, on a quadrille pad, assuming each little square is 70 ohms of resistance, with one amp needing to enter the grid, and realize your PCB layout has the lifetime of that capacitor in your hands.
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If you have moving air, then the CASE can dump heat into the air. Or --- even directly radiate to the other oomponents and chassis.
I recall old TVs with 2" by 4" aluminum electrolyitcs and 2 or 3 or 4 mounting tabs that twisted to lock, and then might be soldered. Good heat flow. But we don't have that anymore.
What do do? With vertical mount of 2_wire caps? Perhaps BEND over the wires, to provide a large wide heat flow path.
This might work for NASA one-of-a-kind power supplies, but not for automated assembly;
On other hand, automated assembly likely has only some warrantee 5_year expectation, not 100 years in orbit or out past the solar flux limit past Pluto or surviving another 2 minutes in a Venus probe-to-800 ° C satellite.
