HDD Dock: Power Switch Electronics

[yefi]

I recently bought a 5.25" dock for my SATA drives. It has a physical power switch for the drives.

When I powered it on, smoke emanated from the dock, and a teardown later revealed that a MOSFET on the board, an Alpha Omega 4407A , had completely fried. Multimeter showed short circuit between source and drain.

I have since read a couple of different reviews of these docks frying. My question is, is this fundamentally a bad way of switching power or is it essentially the right way of doing things, but just the result of poor/faulty components?

Thank you.

 

[mindless1]

Your question does not seem valid. Those 'fets are probably there to step down the power from a 12V AC-DC adapter to the 5V or 3.3V that the SATA drive needs, not really related to the fact that the enclosure has its own power button which should just disconnect the 12V adapter from everything downstream of it, meaning entire SATA bridge board pictured plus the HDD itself.

Was the 'fet faulty? Maybe, or inadequate form factor for the heatsinking available vs the ambient temperature in the enclosure, or there might have been a mains AC power surge that went through the AC/DC adapter to fry it, or a failure of the 12V adapter itself, or if new it could have been defective/garbage from the factory.

SO, yes it is essentially the right and popular way of doing that, but the finer details of whether the entire design was good or some portion contributed to failure are unclear.

If I am understanding that this happened the first time you powered it on, there might be some fault with the PCB that caused overcurrent, or the HDD itself had one. You'd need to individually test everything to rule out contributing factors and sometimes, you won't recreate a power surge so all you can really do is buy a new one or seek a warranty replacement if there is a warranty on it.

 

[yefi]

Thank you for your answer, however I should've asked this on an electronics board tbh.

The dock fitted in a 5.25" bay. On the left-hand side of the PCB you can see the SATA connector where you plug in from mobo and power from PSU. There is no AC/DC conversion. The fet isn't there to step down power, it is a switching device.

I have an identical dock and that one works fine, but I have reservations over the design.

 

[mindless1]

Oh, yes I'm wrong then, thought by dock you meant a USB external. A picture of the whole thing might have helped.

There's nothing wrong with using a fet to switch power, but if that's all it is doing, you could possibly rewire it without the fet as long as the switch chosen is capable of the spin up DC current rating of the HDD.

I'd want to map out a schematic to be sure of what's there first, though a replacement fet shouldn't be hard to swap in with a hot air rework station, if the copper under it isn't destroyed too... except if there is some other PCB defect which caused it to blow in the first place.