WD80EFAX HDD help identifying a component

[peteru]

Long story short, (wrong cable used with a modular PSU), I have 5 dead WD HDDs because 12V was applied to the 5V power input on the SATA connector.

The good news is that after poking and probing the circuit board of one of the WD80EFAX drives, I found a component at the 5V input (pretty much the first thing between the connector and the rest of the circuit) that seems to have failed open. I removed the component and replaced it with a short wire and the drive has spun up again and returned a good SMART report.

I'd like to replace the failed component(s) with equivalent parts. Although the drives may work with the wire links, the failed components did a great job of protecting the HDD and I'd like to retain that characteristics after my repair is done. My guess is that this is some kind of ESD protection. The HDD label indicates that the 5V is rated at 0.7A.

Any idea what is the exact part or suggestions as to what to replace it with?

Pictures of the component are attached.

[peteru]

I guess a process of elimination can narrow down the field. It would not be a capacitor, because it is in series with the 5V power supply. It also isn't likely to be a varistor, because those would usually connect between 5V and GND, like caps. Right?

The most likely candidates would be some kind of a fuse, a resistor or possibly a ferrite bead.

The bottom looks like white plastic or ceramic. Does anyone recognise the marking?

[amyk]

Looks like a fuse. SF-0603F200-2 (see page 3 for marking)?

[peteru]

Awesome! Thank you very much for that pointer. Seems like a 2.0A fuse that did the job it was supposed to do.

Now I have to wait for RS to complete their maintenance on their website so that I can check stock levels and hopefully order a suitable replacement part that is available locally.

[peteru]

The closest part I can find for fast delivery is a 1.5A RS branded part. I'm going to order that and see how it goes when it gets here later in the week.

[fzabkar]

Did you check for shorts? There should be a 5V TVS diode immediately after the fuse.

TVS Diode FAQ:
http://www.hddoracle.com/viewtopic.php?f=100&t=86

PCB protection devices:
http://www.hddoracle.com/viewtopic.php?f=100&t=1615

[peteru]

Very comprehensive and relevant information! Awesome job, thank you for writing that.

I checked the circuit and it looks like the TVS diode protection is still good. Measuring with the diode test mode on the DMM, in-circuit, on the 5V rail I get 0.218V one way and 2.735V the other way. The 12V rail reads 0.218V and 0L. On the low-Ohm range on the DMM, both the 5V and 12V TVS diodes read 0L in either direction.

Checking the two fuses, I get 0.008 Ohms across the 12V fuse and 0L on the 5V fuse.

It looks like a fuse replacement is all that will be required on the WD80EFAX drives.

Not so lucky on the WD10EADS drive, where the the SMOOTH motor controller decided to act like a fuse and released blue magic smoke, vented charred splatter onto the PCB and burned a hole in the padding foam pressed against it. Lucky for me, the other drive in that mirror pair was on a different power supply cable.

$3.80 for the parts, $15 for delivery. Let's hope that the 1.5A RSPro fuses will do the job, otherwise it's a few weeks wait for the 2.0A Panasonic fuses while RS ship them from UK to Sydney.

[fzabkar]

This is why the SMOOTH controller burned up:

Catastrophic failures in Western Digital PCBs:
http://www.hddoracle.com/viewtopic.php?f=59&t=1119

The preamp on the headstack will usually be damaged, too.

[peteru]

I replaced the blown 2.0A fuses on the 5V rail with 1.5A RS branded fuses and all the WD80EFAX drives have been working fine for about a week now.

Thanks for all the help. It was a scary, but educational experience. It looks like I was relatively lucky in that the Hitachi designers got the TVS protection working as intended on the WD80EFAX drives, unlike the WD designers on the WD10EADS drives.