A Look Inside
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The input filtering starts at the AC receptacle, with the PCB there containing an X capacitor, a common-mode choke and a Y capacitor. The main PCB adds another X-capacitor, another coil, two Y-capacitors and two MOVs. For a $30 unit, it’s pretty good. The unit uses four diodes in place of a bridge rectifier. They are rated at 3A. Assuming 77% efficiency (which is about what this unit achieved during the load tests), they will theoretically allow the unit to deliver about 530W from a 230V input voltage and about 277W from a 120V input. It’s not enough for a so-called 550 Watter. The switching transistors are Jilin Sino Microelectronics 3DD13009Ms rated at 12A. I have known similar parts to deliver more than just 260W in other power supplies. They may have failed here due to inefficient secondary rectifiers, or thin heat sinks. That yellow box in the corner just near the primary heat sink sure looks like a passive PFC inductor. I wonder why the power factor was so low. Let’s take a closer look at it, shall we?
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Well, it looks like we have a fake PFC coil. The wire just goes in and straight back out again, but hang on, something just doesn’t feel right here. If it’s just an empty box, why does it feel as heavy as it does? Let’s disassemble it further.
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Have a good look at the above right picture. Not only did they use iron plates to make the fake coil heavier, but that greenish one is actually a floor tile!
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As I said before, this unit only has a single 12V rail. The fact that there is only a single group of 12V wires gives this away. The capacitors used are ChengX on the 5Vsb and 12V rails and BH on the other rails, both of which are typical Chinese no-name junk. The soldering quality isn’t great either, with a lot of the component legs being left too long, but I’ve seen much worse.
None of the rectifiers are good enough for the labelled current ratings. The 3.3V and 5V rails are both rated at 24A, but only use 20A MOSPEC S20C45C Schottky rectifiers. The 12V is supposed to be able to deliver 38A (18A + 20A), but the rectifier used isn’t even rated for half that! I couldn’t identify the manufacturer or find a data sheet, but the part number suggests it’s a 16A fast recovery rectifier.
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“I am Legend” says the fan. After removing it, I connected it to another 12V power supply and it spun, so the problem was with the fan controller. For obvious reasons, I can’t comment on fan noise. The heat sinks have good surface to air contact, but are very thin, so they won’t conduct the heat from the transistors and rectifiers to the fins as well as thicker heat sinks would.
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