Good morning. Our weather is proving fickle to forecast this summer, with pesky low probabilty rain making another appearance yesterday and giving us another unexpected soaking. Today will be another wet one going on what I see through the window.
I have made a living out of electronics for the past 40 years and throughout that time, if you wanted to find a fault on an ageing circuit, the power supply was always the best place to start, with the component that tends to die of old age first being electrolytic capacitors ( that's those with a tubular shape ). The electrolyte eventually finds a way through the casing and as it starts to dry out, the capacitance goes down. Some caps also corrode internally, producing that bulge on top, or blow a relief plug in the base.
The most common job of these capacitors is to smooth out a voltage rail (much like an accumulator in a hydraulic circuit) and keep a dc voltage steady. In truth the voltage is never perfectly steady, there is always what designers call "ripple" on top of the dc (if you look at it on an oscilloscope, it looks like waves rippling on the top of a deep pond). The lower the capacitance, the bigger the ripple, until eventually the dc level (the bottom of the ripple) is too low for the circuit to work anymore. Also the current that is constantly rushing in and out of the capacitor warms it up and the higher the internal temperature goes, the lower it's life expectancy will be. Electrolytic capacitors tend to have a huge range of manufacturing tolerances too (typically plus or minus 20% or more), so it's not that surprising that if the designer hasn't taken everything into account and then applied a good safety factor, the cap will be the part that lets everything else down.
RNG, I can tell you how to work out the capacitance with your meter and a resistor, but by the time you have the old capacitor de-soldered, it's as easy to put in a new one for the little they cost.
