On Tue, 18 Nov 2008 13:23:57 -0800 (PST), "borat.gunter"
<borat.gunter@googlemail.com> wrote:

>On 18 Nov., 21:39, bok...@zonnet.nl (Gerard Bok) wrote:
>> On Mon, 17 Nov 2008 13:00:54 -0800 (PST), "borat.gunter"

>> <borat.gun...@googlemail.com> wrote:
>> >one friend just plug the 4 pin power connector in the wrong way to her
>> >hard disc.

>But I am curious about the schematic part of such circuit. How does
>the subcirciut work. No only in oder to fix it, more like the
>principle.

The principle is easy.
You have your +12 volt which is used for the motor only.
(Correct me if I'm wrong.) You won't hurt the motor circuit with
5 volt.
And you have your +5 volt for the logic. 'Logic' are the parts
that will usually explode rather spectacular if exposed to
voltages over 7 or 8 volt.

>I was thinking that the burn component were a fuse-like thing, which
>would be sacrificed in order to protect the parts behind.

That would make sense. Were it not that such a circuit would add
a dime to the manufacturing costs :-)

>After discussing with my co-worker I think the hardware vendor would
>pay more attention or effort on fuse-like component, since the
>connector alone is really hard enough to connecte in the reverse way
>which my friend did.

It would require both a fuse and a pretty big zener type diode.
Practically, this goes by the name crowbar and is implemented
using a fuse, a zener diode and a thyristor. Common in a PSU but
I've never seen them on harddisk controller boards.

>Any schematic reference would be really helpful.

Sorry. The most recent schematics on harddisk I have at hand are
probably 20+ years old.

--
Kind regards,
Gerard Bok