Introduction
Wall mounted power supplies for small appliances are often thought of as cheap (<£10) throw-away items, but it is sometimes easy to repair them. Most people have a drawer-full of such items left over from failed/redundant appliances, but they are often the wrong voltage, amperage or connector type.
This guide shows that sometimes a repair is as simple as replacing a capacitor taken from an unused /unwanted adaptor, so there is zero cost. Thus I repaired my mini dehumidifier with a failed 9v 3A power supply.
Such a small power supply is also know as a 'wall wart', 'AC adaptor', 'power adaptor', AC/DC power adaptor' or 'power brick'.
Tools
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First image shows a repaired AC/DC adaptor where the plastic housing has been opened and glued back together and tie-pull added for extra safety.
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Second image shows the adaptor housing split in two to reveal the printed circuit board (PCB). The PCB may be orientated in either direction. To split open the glued housing, place the adaptor in a vice or similar and squeeze the body with different positions and pressures, until you hear a glue crack (best wear safety specs).
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Most times the housing will fracture along the glued joint line, such that it can be safely glued back together. If the housing is otherwise damaged, it's not safe to continue with this repair.
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With the PCB exposed, look for any electrolytic capacitor that is bulged or leaking. In the image it was the separate green capacitor that was in the arrowed position and showed the top bulging with a leakage black spot in the middle of the top. Ensure there is no other damage eg blackened resistors, corroded areas etc, if present abort the repair.
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With a soldering iron and some added solder, extract the faulty capacitor.
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If you have a capacity or ESR meter, you can confirm that the extracted capacitor is out of specification eg mine showed 53uF not 1000uF and 53ohm not 0.1ohm.
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Replace the extracted capacitor with a good one. Note the polarity, the negative lead on the darker side normally printed on the PCB. You can take a good capacitor from an unwanted adaptor. Check it has the same capacitance and at least the same voltage which is printed on it. (Temperature rating is probably the same.)
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Glue the cover back on and maybe add a tie pull for extra safety. Hopefully, if like mine, it will now be working again.
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Replacing a bulged electrolytic capacitor in the AC adaptor got it working again.
