Help me identify this Chip (from a HDD)

Thread Starter

inoskyh

Joined Apr 11, 2015
13
Hello AAC community!

I'm here to ask for your help: my sister have an old HDD (extracted from a media center) that didn't boot anymore (disk do not spin when powered), but obviously, there is a lot of important stuff in it :)

I noticed that when powered up, a particular IC comes hot (and smells...) so much that solder starts to melt on its pads!
This component is a SMD and looks it's polarized (there is a line on the package, close to one of the two pins).
According to this SATA diagram, the component is directly connected to 12VDC and it looks it acts as a watch guard for the rest of the circuit (12VDC rail powering all around the PCB).

IMG_1661.JPG

I wondered if this IC was kind of a diode, but surprisingly, the line is drawn on the connector side (input), it's a non sense for me: when block the current from 12V but distribute it via a power rail? So I tried to soldered a SS34 in place, but no result (at least, it does not melt).

I can read the following inscription on the package:

ST E (STMicroelectronics logo)
BUF
C811​

IMG_1660.JPG

I started to look for such component on the web... but found nothing exact match, only approaching results:
- from STMicroelectronics
- from digikey
Is the component obsolete (great chances, according to the age of the media center)?

Do you have any hints / explanations / guidances? Even if the component, I'm afraid something else is broken on the circuit but I have the intuition that a component so close to the 12VDC input should act a the guard and protect the rest of the circuit? Am I right?

Enclosed, some photos of the component and circuit.

Cheers,
Nicolas
 

Thread Starter

inoskyh

Joined Apr 11, 2015
13
Right but this IC is connected to ground according to SATA connector diagram.
I think it should be a cap, I'll verify (maybe you were thinking of another measurement?)
 

Thread Starter

inoskyh

Joined Apr 11, 2015
13
Hola there, thanks for your replies

Are both the same?
No its not the same chip (no printings on the package).

See if you can find an identical HDD on ebay for example and try changing the board.
Good idea, but I'm afraid the drive is too old to find anything close on ebay. I'll give a try nonetheless.

I guess it is an overvoltage protection device lika a transil, and the drive whould work fine even without it in place.
That was my first guess. What is a transil exactly? I'll try removing the IC and do a short between its pads next time.

It looks like the USS Montana.
Sorry for the mistake on the title, its chip (not ship :)) But I can't edit my posts.

Cheers,
Nicolas
 
Last edited:

RamaD

Joined Dec 4, 2009
328
It is SMBJ13A Transil from ST Micro! BUF is the topside marking for this part.
We should have some codings for topside markings for easy identification, unlike the present arbitrary markings, or maybe, I am not aware of one if it exists!
 

JUNELER

Joined Jul 13, 2015
183
Hi,
can i know first what system you have... motherboard type and processor type and the O.S you used.

secondly a satadrive had a 5v supply not 12v.So verity the pin assignment of the satadirve so we can measure
the input coming from the power supply going to that sata pins.we are talking about the pins of vcc and not data pins
 

AlbertHall

Joined Jun 4, 2014
10,397
That was my first guess. What is a transil exactly? I'll try removing the IC and do a short between its pads next time.
No, don't do that. Try it with the chip simply removed.
It is an overvoltage protection device which conducts to limit ant excess voltage and it has apparently become short circuit.
 

Thread Starter

inoskyh

Joined Apr 11, 2015
13
It is SMBJ13A Transil from ST Micro! BUF is the topside marking for this part.
We should have some codings for topside markings for easy identification, unlike the present arbitrary markings, or maybe, I am not aware of one if it exists!
Hello RamaD, thanks a lot for the reference!

Hi,
can i know first what system you have... motherboard type and processor type and the O.S you used.

secondly a satadrive had a 5v supply not 12v.So verity the pin assignment of the satadirve so we can measure
the input coming from the power supply going to that sata pins.we are talking about the pins of vcc and not data pins
I don't think this is related to my config. Drive's disks just don't spin and drive simply does not bootup when powered, so the problem comes from the disk.

No, don't do that. Try it with the chip simply removed.
It is an overvoltage protection device which conducts to limit ant excess voltage and it has apparently become short circuit.
So am I right to think that if I measure continuity between the damaged transil pins, it should pass either way? I must re-verify but I think it is what I observed.
What I don't understand is: if I remove the component, how the 12VDC rail downstream (that seems to be connected to the component) is powered?

Thanks for all your answers
 

Thread Starter

inoskyh

Joined Apr 11, 2015
13
The device is connected between the supply and ground, not in series with the supply.
https://en.wikipedia.org/wiki/Transient-voltage-suppression_diode
Oh that makes a lot of sense now!
Obviously... what I saw as a 12VDC rail (all around the board) is instead a ground pour... dummy me.
I'll de-solder the diode and see if the drive boots up.

I'm still quite surprised... such a ship really dies with time? Why it just burned up? Does it could have damaged other ICs on the board?

Thanks a lot AlbertHall
 

kubeek

Joined Sep 20, 2005
5,733
These Chips are designed to fail shorted, usually after they have done their job of protecting the supply rail from severe overvoltage.
 
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