I've always carried out my own repairs on my Amigas (and everything else), but recently, with the resurgence in popularity of retro computing, I've had a number of people come to me with their Amigas in need of repair or refurbishment. It's very satisfying to be able to help keep these old machines running and in tip-top shape!
Besides myself, there are a surprising and growing number of Amiga users who carry out repairs on our beloved machines. If you need your Amiga repaired or would like its capacitors replaced, there might even be someone local to you! I've started compiling a list of people you can have your Amiga repaired by - click here for details.
One of the main failure points of Amiga computers these days is their capacitors, specifically electrolytic types and particularly the surface mount variety. These were used throughout the A600, A1200, A4000 and CD32, and seem to have a limited life span of around 20 years. Once they start dying, they start to leak their electrolyte all over the motherboard, slowly corroding the tracks and eventually destroying some circuits. Their lifespan can be extended by regular use, but ultimately these capacitors will leak sooner or later, and given the fact that many Amigas have spent a lot of time in storage, these things are little time bombs waiting to destroy your beloved machine. The problem is compounded by the surface mount technology being relatively new (and thus only used for the later Amiga models), the use of cheap capacitors by Commodore, and the fact that these capacitors leak from their underside directly onto the PCB, rather than through safety vents in their cap as traditional electrolytic capacitors do.
Failing capacitors can often be difficult to spot as they don't always show obvious symptoms until they've already stopped working, leaked and destroyed some other circuit on the board. Often the symptoms are only slight and gradual (was the picture always that fuzzy or the audio always that dull?), and if the capacitor's on the power lines you probably won't see any symptoms at all. Looking at the capacitors themselves can give some clues that they're in the process of leaking, as the PCB around their bases can be stained and their solder joints dulled. Fortunately the parts are cheap and can be easily replaced by anyone competent at soldering surface mount components, so they can be replaces as a preventative measure. Capacitor technology has come a long way in the last 25 years, so even today's cheapest capacitors should easily outlast those Commodore used a quarter of a century ago, and top-end capacitors should probably last the computer for the rest of its life (and yours).
If left for long enough, traces on the mainboard will eventually be destroyed completely, resulting in failure of the machine. Some failures might not be immediately obvious, whereas others could stop the Amiga from working at all. This video shows an Amiga 600 whose capacitors had leaked for long enough to damage both the audio and video circuitry. Video was fine on composite output, but the RGB port was totally missing the red component. On the audio side, the amplifier feedback loop was destroyed on the right channel, causing the sound to be totally distorted.
Other surface mount components can also fail, though this is far less common and far less predictable than failing electrolytic capacitors. They won't cause PCB damage when they fail, and will normally have an obvious symptom such as sound failure or missing colours on screen, or no symptoms at all in which case they probably don't need to be replaced.