St Bux C441??

I have a 200G Barracuda hard drive that keeps the power supply from turning on when it's plugged in.

The +12v pin was found to be 0.4 ohms to the GND on the ohms (not diode check) multimeter setting, regardless of the direction of the leads. This meant a shorted power component which is actually good news. I found the source of the short on my first try. The component is a dead short and once it was taken out there is no low impedance path from +12v to GND.

There's a small black rectangular 2-lead SMD pkg here, like a cap or power diode might come in. The kind where it's got wide pads coming out the sides that wrap underneath the component. It has a line on one side so it's a polarized component. The line side is connected to the +12v pin, the other goes to a conductive pad that a grounded case screw goes through.

It is an ST part. It is labelled:
BUX
C441

What is this component?

ST's website lists a number of components with "BUX", none with a suffix like C441, and they're all NPN transistors which this 2-terminal device is most certainly not. A web search got hits for parts finders but no description or spec sheet.

I could see it as being a cap- which makes sense where it is, and the direction of the polarizing line- but this is NOT a marking you'd expect to see on a cap (no capacitance or voltage listed). Also I already found a cap from the +12v pin to GND. Next thought was a transient voltage suppressor (zener diode) to clamp a voltage spike to ground, though I have no evidence to support this.

Sounds like a protection Diode to me.

Like a zener protection diode to protect against overvoltage, or just a normal rectifier diode to protect against reverse voltage?

Would a zener (transient voltage suppressor,transorb) protection make sense? I mean, I figured a hard drive is pretty sensitive to overvoltage but due to a lack of accuracy in zener voltages the zener selection would have to be a considerably higher voltage than 12v to guarantee it never conducted under normal operation.

Why would you even need to protect against negative voltage on the 12v line in a computer? Some "just-in-case" kind of thing?

Should I just try to run this drive without replacing it with anything?

No it protects against voltage spikes etc. It actually protects the components in the power supply and the Drive. It provides a ground path for the spike. They use them on Relays and Solenoids and Motors. As the field winding colapses it generates a voltage or spike. This can dammage other components that are sensitive to these reverse voltages.A 1n2004 can do the same job.

I found an SMD 1N4004 and put that in.
Drive seems to work fine, which is good, I not only needed the 200GB but there was a LOT of my stuff on that drive!

Damn... apparently this was the problem which led me to replace my power supply, motherboard, and eventually buy a whole new processor, motherboard, and memory combo. I was sure I tried it without that hard drive attached. Well, they were all obsolete anyways.

nice work troubleshooting!

Luck mainly. I had to face it- that was probably the ONLY faulty component I would be able to find troubleshooting, and one of only a few I would even be able to replace if I knew if was bad. Well, I was unlucky to have a diode fail like that and kill my system. But another way of looking at it is if you're going to have a failure, being a diode is fortunate.

I was just really, really lucky on this one. Glad my entire mp3 collection wasn't lost!

More dead drives related to BUX ZZZ

Hi,

I have heard of two other instances of dead drives that sound like this and now have one myself. I've bought 4 similar drives from ebay to have for comparison measurements.

It seems like mine is also the ST BUX part. Like the original poster I tried searching for it but found no datasheet on it.

An interesting item is the part number for this component. Each drive has a different part number on it.

PCB 100299703 D 7609CUUG has BUX C521 2.1 hm (short)
PCB 100299703 D 75088J0B has BUX C424 8.0 KOhm
PCB 100299703 E 66150Y02 has BUX C532 20.2 KOhm
PCB 100387560 K 3709VCHY has BUX C625 13.8 KOhm

Does anyone have any idea why each might have a different number after it?

I've swapped the part and the drive now works

In my opinion this is feeling like an issue with the Seagate design. Its the first drive I've had in 20 year that wuldn't even spin up. And now it sounds like there are other instances if this as well. I understand the intent of protection but there are ways that are not catastrophic to the product.

Cheers, Craig

Many thanks

Thank you all for these comments.

I was virus-scanning a Seagate Barracuda 160GB drive this afternoon when it began to smoke - now even I know this is not a good sign!

Fortunately, since it was out of the case, I could see the smoke coming from a "BUX C521" and google was then good enough to bring me here.

For the record, the PCB is labelled: 100282774 F 7608UF84

I was reading 1hm: 12V to Gnd, which translates to a drive drawing 150W or something, if I remember my school physics correctly - evidently the reason for the smoke is revealed!

Not having too many parts to hand, I have just clipped out the offending diode and although this is rather a "penny in the fuse-box" approach, the drive is running fine on a nice smooth power supply. It's backing up now, and as long as it lasts long enough to recover my data, that's fine with me!

I think we can say that anyone with a Seagate drive which won't spin up, and in particular is drawing masses of power should look critically at the diode between 12V and gnd.

Many thanks again.

Chris

I have a 160GB seagate Hard disk. I put them in an external enclosure. Today, I plug in my laptop AC adapter. The whole thing is dead. then I put the HD to the computer, but the computer can not boot. I checked the ST BUX C449. It is short circuit. I went to ST.com, but I can not found the part description. Then I googled found this forum. It helped me so much. Thank you guys for the information.

Thanks, thanks, thanks to this forum and the people that post.

In my case a Maxtor 6y080lo
exactly the same problem and solution as Chris_Goddard post.
except it was a bux c507, clippid it out and it run again.

Ok my computer will not turn on when the drive is connected.

Drive is the same as 'arkadas'

Which one is the ST Bux component. There is the ST BUX C642 which is the larger rectangler component to the right an a smaller more rectangle component on the left which i cannot barely read any markings on
Which one to pull out?

Ok. all ok.

Removed the component marked ST BUX C642 on the logic board and was able to recover the data. yesssss!

HI, The ST diode is marked and mean as follow.

on upper right an E caracter mean that is lead free component.
the BUX is the Marking of component
the C633 , means respectively (C=) manufacturer location, (6=) year of production, (33) is week of production.

Steve

hi,
i faced the same problem,short diode on 12v power input, on a ST3500630AS Barracuda 7200 10 HDD.The code of the diode was 743 LEM i just replace it with a BUX C044 after reading your posts. The drive is back with 500 GB of data. Thanks to all of u.