5TB WD MyBook Overvolted/Diode Replacement

[Ju1es]

Hi all,

This weekend a friend of mine made the mistake of connecting a 19VDC laptop power supply to a 5TB WD MyBook external drive. After doing some light reading about the consequences of doing so, I volunteered to take a look at it for him and at least determine what he should do. I'll preface by saying that while I have some entry-level electronics experience, I'm treading lightly as I've not performed SMD component repairs before.

I received the drive yesterday, disassembled the enclosure and began inspection. The bridge PCB had no obvious signs of damage. I plugged the drive into a SATA to USB adapter and noted that the drive does not spin. After removing the drive PCB, I immediately noticed that the foam pad over the PCB had melted onto the TVS diode on the 12V rail. Explains the burning smell my friend mentioned. The drive PCB is 2060-800001-002 REV P1.

I started taking measurements and found that the 12V rail is shorted to ground. The TVS diode at position D4, as well as what I understand to be the Schottky rectifier at position D6 were measuring shorted. They measured from .000 to .004 in diode mode, which is also the 2K ohms setting on my meter, in both directions. The 0-ohm resistor (marked in blue in the attached photo, not sure if the position is labeled) was continuous. The 5V TVS diode and Schottky rectifier (D3, D5) measured OK, both about .137 forward and O.L. with leads reversed.

I ordered 10 SMBJ12A diodes from Mouser, removed the burned TVS diode on the 12V rail, cleaned up, and re-measured. The short to ground on 12V remains. The included pictures are from after removing the diode. I figure the next step is to remove D6 and see if that resolves the short, but I wanted to ask some questions before I do that.

Firstly, other than a donor board, what can I do to find a replacement for that diode? The only marking I can see on it is "7". I'm resistant to buying a donor board as, to be honest, I'd like to avoid spending the $50 bucks, but I also don't want to remove components without having access to a replacement, even if only for my own assurance.

Secondly, do these rectifiers fail when the drive is overvolted, and would that cause the short to ground? I interpreted from what I read that the Schottky rectifiers are usually not the cause of a short when an overvoltage event occurs, but I absolutely could be misunderstanding.

If it's a reasonable idea to remove/replace the diode, I can do that, but if that doesn't resolve the short I'm going to recommend that my friend visit a professional, as I wouldn't be comfortable doing something like getting a donor and transplanting the BIOS IC or another more involved repair.

Thanks in advance! And sorry if the post was long winded.

Attachments

Close up of the 12V area, TVS diode removed. D6 in red, 0-ohm resistor in blue

Back of the PCB, model number visable

Front of the PCB

[Lardman]

Those don't normally blow unless the polarity has been inverted it can be treated the same as the TVS. I'm sure fzabkar has posted replacement codes in the past but getting stock levels at the moment appears to be a problem.

WD replacement PCB's are dirty cheap even over this side of the pond a replacement from ebay is only beer money and it will give you all the components you need - you don't have to swap the rom and use the board just nick the diodes.

[Ju1es]

Thanks for the info Lardman! I appreciate it.

Shortly after posting I removed the Schottky, and the short was gone. There was a time constraint on this job, so I ended up purchasing a similar WD drive from a local seller on eBay and harvesting the diodes from it. Worked out great, drive spun right up.

I just wanted to come back and say thanks to the forum, the depth of information being shared is awesome and I'll be sure to keep reading and learning more from you all.

Thanks again!