cameo wrote:
On 4/26/2015 3:05 AM, J. P. Gilliver (John) wrote:

5.12V and 12.38V

I'd say acceptable, though a bit high.

After connecting the power supply to the HD:

4.73V and 13.57V, respectively.

Hmm. Most TTL ICs used to be specified to work over 5 ±¼V; the CMOS
equivalents are usually tolerant of a broader range. I'd have said that
that probably _would_ still work (though that's at the connector; could
be lower at the actual ICs).

This doesn't make sense. The 12V pin's voltage should also drop under
load, not just the 5V pin's. Even the 5V pin voltage seems to drop too
much IMHO, especially since there is no USB load on it. I assume the
12V is used to spin the HD platters.

That's the usual assumption. Although that's very high, I would _hope_
it hadn't fried anything.
[]
Next, I think, I'll try to see if I could remove the IC board to see
the component side of it if there is some visible scorching on a
component. I would have done it already if I had the right size torx

A lot of these boards have a surge-suppression device across the supply
line, which rumour has it can fail short (possibly without any visible
sign); I'm not convinced, but if it has, it'd stop the power reaching,
and unsoldering one end is not that difficult. But if that's the case,
the voltage should almost disappear under load ...

What if the polarities were reversed, not just applying the 12V where 5V
was called for and vice-versa.?

If you put your ear very close to the drive when you apply power, can
you hear _anything_? With mine where the head was stuck to the surface,
I heard a little tinkling or ticking - I presume that was the head
swinging mechanism trying to move.

Not a sound from my HD.

screw driver the board is attached to the HD body. Then I might also
visit some eRecycling stores to find the exact same WD HD and
cannibalize it for its circuit board. Fortunately this seems to be a
fairly ubiquitous HD about 10-12 years ago. So maybe I get lucky.
Looks like a fun project, doesn't it? ;-)

Yes. Are you planning to continue to use the drive, or just intending to
rescue the data on it?

Just rescuing the data on it. The drive itself is not much worth these
days anyway.

If it comes to opening it, unless you've got a
_phenomenally_ clean room, I'd stick with the latter; if replacing the
board works, you _might_ be OK, though unless it's a particularly
expensive drive, I'd probably still not trust it.

Thanks for the tip. I'll keep it in mind.



The reason the supply has readings like this:

4.73V and 13.57V

is the 5V rail is heavily loaded, the supply turns up
a common mode control for the shared transformer, and
the 12V gets elevated higher than it should. This is
called cross-loading on ATX supplies. They used a shared
transformer (one AC transformer driven by the switching
circuit), and the turns ratio of the transformer
establishes the normal potentials. When one rail is
heavily loaded, the switcher tries to compensate by
turning up the shared transformer. It is the combination
of seeing 5V rail going low, plus 12V rail going high,
that tells me:

a shared transformer supply is involved
the 5V rail is overloaded

The disk drive has components on the power entry points,
right after the Molex 1x4 power connector. There is
overshoot protection, for hot insertion and removal
of a hard drive. Even the IDE drives had this form of
protection. It is there, to snub "sparks" if the power
cable is pulled while the drive (and motor) are still
spinning. It's so an overshoot on the DC rail,
doesn't damage something. The components doing this,
are only rated to stop transients, and they burn up
if presented with a permanently out of spec voltage.

A poster once, came to the newsgroup with a drive problem.
And he figured this out on his own. There were a couple
burned components right after the power plug. And the power
supply had overvolted both rails. Removing those burned
things, got the drive running again, long enough to
get the data off.

On modern drives, I don't see the exact same component
configuration. I expect there is still overshoot
and undershoot protection on the rails, and if you
apply either reverse potential or swap 5V and 12V,
that some of those components get burned. On older
IDE drives, the components are facing outwards and
you can do a visual check near the power plug area, for
burn marks.

As for the strange Chinese adapter, if you own a multimeter,
you'd want to check the power plug end first, before
connecting it to something. You can "buzz" the enclosure,
from external four pin miniDIN to where the internal
wires show up on the adapter board in the enclosure,
to figure out the "pinout". Then with the Chinese
adapter powered but not connected, see if the voltages
on the Chinese end, make sense for how the enclosure
is wired. So you can figure out whether there will
be trouble, before plugging it in. You need the "ohms"
range on the multimeter, to buzz out the wiring on
the enclosure. And "volts" to check the Chinese adapter,
before a calamity happens. I end up doing this
sort of checking all the time, with those damn
barrel connectors (some of which are center "+"
and some are center "-").

Paul