Disassembly
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The input filtering is inadequate, consisting of just two Y-Capacitors, and no X-Capacitors or Coils. Four 3A diodes are used in place of a bridge rectifier and the two primary capacitors are 560µF parts from Zhila, a brand I’ve never heard of before. The switching transistors are Huashan KSH13009s, rated at 12A each in the dated half-bridge configuration. As you can see from the above right picture, one of them blew itself in half. The PWM controller that drives them is located in the secondary side. It’s a BCD Semiconductors AZ494A. This and similar controllers are commonly used in half-bridge designs.
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The capacitors used on the secondary side are a grab bag of LTEC, Zhila, and HQ, all of which are of questionable quality. There is also a single Nippon Chemi-con capacitor on the 3.3V rail. Unfortunately, it’s a KZG series, which, while the manufacturer typically makes great caps, is one of Chemi-con’s dud series, which are no more reliable than cheap chinese parts. There are also no PI filtering coils, and there is only one capacitor on the 12V rail, which is why the ripple was somewhat high.
The 12V rectifier is an MUR2020CT Super Fast Recovery Rectifier rated at 20A. It would have been preferable to use a schottky rectifier, as they offer better efficiency. The other two rectifiers are SB3040ST Schottky rectifiers, rated at 30A. These rectifiers are all good enough for what the label claims about the rails. The secondary side is controlled by a BCD Semiconductors AS339.
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The soldering is quite tidy and well done, or rather, it was until the explosions. The pad below the middle leg of one of the switching transistors has completely burned up, and there is soot on the PCB.
There are also burn marks on the case and on the plastic insulation sheet under the PCB.
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As mentioned earlier, the fan is branded HXS. It is wired directly to the 12V output, and was audible. There was sufficient oil in the bearings, thankfully. The heat sinks are fairly thick, and have decent surface to air contact. They did their job just fine until the attempted overload.
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