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Introduction
The adapter works and the output voltage measured is correct, but it does not work when connected to the device being powered.
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It is a standard 220 VAC to 12 VDC power supply with a maximum consumption of 2 A.
Ask FixBot
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When connecting the multimeter to the adapter without a load, it shows the nominal voltage.
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However, if we apply a load, the voltage drops too much depending on the consumption; in this test at 480 mA, it drops to almost half, and with another 80 mA load, it dropped to 10 VDC.
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With this test, we have verified that the adapter works, oscillates, and the AC input is apparently fine. The suspicion may lie in the secondary circuit, so we disassemble it and check the circuit.
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There are several techniques to break the classic ultrasonic seal on this type of power supply; I used a heat gun on the seam to soften the plastic and then used a utility knife to cut along the welded joint, then gently pried it open with a pocket knife or a flathead screwdriver until it opened.
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Once opened, the first thing I noticed was the condition of the capacitors; in this case, the output capacitor located next to the triac is the one that is damaged, while the others are not. It wasn't like this, only swollen, but it deformed when I desoldered it, and I repositioned it to take the photo.
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The capacitor it uses is 1000 microfarads and 16 VDC.
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In this case, it is important that it be the same size because the space is very limited.
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The capacitor is replaced with an identical one and it fits perfectly into the charging board. Sometimes, if you have more space to work with, you can use a capacitor with a higher voltage and adapt it to the space so that the housing can be put back on.
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All that remains is to reassemble the housing and glue it back in place.
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Note: I did not photograph the test I performed with the resistive load, where the adapter did not drop below 12 VDC, perfectly supporting the 480 mA draw.
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The most common failures in these cases usually come from the capacitors. In my case, I only replaced one because I did not have the others of the same size or capacitance, but it is best to change them all, especially if they are on the secondary side. An interesting fact is that "low ESR" (low equivalent series resistance) capacitors are better for durability.
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To reassemble your device, follow these instructions in reverse order.
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