Unusual drive failure - 12v line short

In article , Franc Zabkar
writes

It's common enough. There will probably be two TVS (transient voltage
suppression) diodes, one across the +5V rail, the other across the
+12V.

You're right. I took the board off and there is a SMT diode on the
hidden side across the 12v line, and it is reading a short. I suppose
it could be the motor controller chip that's shorted, but it looks
intact.

You can remove the shorted diode and the drive should work
without it. Just make sure your power supply is good ...

I'll take the board into work, remove the diode today and report back.
Thanks. 250gb is still a useful capacity to have. The drive's in a
personal video recorder, not a PC, and this PVR is known to have a weak
PSU.

--
(\__/)
(='.'=) Bunny says Windows 7 is Vi$ta reloaded.
(")_(") http://imgs.xkcd.com/comics/windows_7.png

Robert Nichols wrote:
In article ,
Gerald Abrahamson wrote:
:
:Most modern drives (within last 5 years or so) have a very
:long expected lifetime (MTBF = 250,000 hrs = 28 years
:running 24/7, and 500+k hours is more typical today).

The units for MTBF are not hours but device-hours, i.e., the product of
the number of hours and the number of devices being observed, and that
rating applies only during the device's rated service life, which is an
entirely separate parameter.

MTBF of 250,000 is almost totally unrelated to the expected service
life. It is quite possible to have a device with its MTBF 250,000 and a
rated service life of 1 hour. It just means that if you ran 250,000 of
those devices for one hour you should expect 1 failure. Once a device
passes its rated service life, the MTBF rating no longer applies.
Think: a battery used to provide power to a missle's guidance system --
built to be highly reliable for the short time it's needed, and pretty
much assured to go dead not long after that. High MTBF, short service
life.

Looking at the power-on hours and corresponding normalized SMART value
on a few fairly recent drives, it appears that the SMART warning due to
power-on hours would come at about 10 years of power on.


That is total BS. MTBF is per device. Read, for example, MIL-HDBK-217.
--
Cheers, Bob

In article , Clint Sharp
writes

More likely to be a transorb but most likely to be the motor driver IC.

They usually burn up when they fail, and this one looked fine. Took out
the shorted diode and the drive span up ok. Not yet tried it.

--
(\__/)
(='.'=) Bunny says Windows 7 is Vi$ta reloaded.
(")_(") http://imgs.xkcd.com/comics/windows_7.png

In article , Mike Tomlinson
writes

I'll take the board into work, remove the diode today and report back.

Took out the shorted diode today and the drive span up OK on a PC power
supply. Not yet tried it in the PVR but am sure it will be OK.

Thanks everyone for your suggestions.

--
(\__/)
(='.'=) Bunny says Windows 7 is Vi$ta reloaded.
(")_(") http://imgs.xkcd.com/comics/windows_7.png

In article ,
Bob Willard wrote:
:Robert Nichols wrote:
: In article ,
: Gerald Abrahamson wrote:
: :
: :Most modern drives (within last 5 years or so) have a very
: :long expected lifetime (MTBF = 250,000 hrs = 28 years
: :running 24/7, and 500+k hours is more typical today).
:
: The units for MTBF are not hours but device-hours, i.e., the product of
: the number of hours and the number of devices being observed, and that
: rating applies only during the device's rated service life, which is an
: entirely separate parameter.
:
: MTBF of 250,000 is almost totally unrelated to the expected service
: life. It is quite possible to have a device with its MTBF 250,000 and a
: rated service life of 1 hour. It just means that if you ran 250,000 of
: those devices for one hour you should expect 1 failure. Once a device
: passes its rated service life, the MTBF rating no longer applies.
: Think: a battery used to provide power to a missle's guidance system --
: built to be highly reliable for the short time it's needed, and pretty
: much assured to go dead not long after that. High MTBF, short service
: life.
:
: Looking at the power-on hours and corresponding normalized SMART value
: on a few fairly recent drives, it appears that the SMART warning due to
: power-on hours would come at about 10 years of power on.
:
:
:That is total BS. MTBF is per device. Read, for example, MIL-HDBK-217.

In a brief perusal of that document (scanned copy -- no search function
available) I do not find the term "MTBF" mentioned anywhere, so I fail
to see why you would consider that document the definitive work on the
subject.

OTOH, I spent 26 years designing high-reliability electrical and
electronic equipment and do have some idea of what I am talking about.

--
Bob Nichols AT comcast.net I am "RNichols42"

In comp.sys.ibm.pc.hardware.storage Robert Nichols wrote:
In article ,
Bob Willard wrote:
:Robert Nichols wrote:
: In article ,
: Gerald Abrahamson wrote:
: :
: :Most modern drives (within last 5 years or so) have a very
: :long expected lifetime (MTBF = 250,000 hrs = 28 years
: :running 24/7, and 500+k hours is more typical today).
:
: The units for MTBF are not hours but device-hours, i.e., the product of
: the number of hours and the number of devices being observed, and that
: rating applies only during the device's rated service life, which is an
: entirely separate parameter.
:
: MTBF of 250,000 is almost totally unrelated to the expected service
: life. It is quite possible to have a device with its MTBF 250,000 and a
: rated service life of 1 hour. It just means that if you ran 250,000 of
: those devices for one hour you should expect 1 failure. Once a device
: passes its rated service life, the MTBF rating no longer applies.
: Think: a battery used to provide power to a missle's guidance system --
: built to be highly reliable for the short time it's needed, and pretty
: much assured to go dead not long after that. High MTBF, short service
: life.
:
: Looking at the power-on hours and corresponding normalized SMART value
: on a few fairly recent drives, it appears that the SMART warning due to
: power-on hours would come at about 10 years of power on.
:
:
:That is total BS. MTBF is per device. Read, for example, MIL-HDBK-217.

In a brief perusal of that document (scanned copy -- no search function
available) I do not find the term "MTBF" mentioned anywhere, so I fail
to see why you would consider that document the definitive work on the
subject.

OTOH, I spent 26 years designing high-reliability electrical and
electronic equipment and do have some idea of what I am talking about.

No need to sling documents around. Even the name says it is
a failure probability per time, not a life time. Probabilities
are not individual counters and so a "per device" does not apply,
given statistical independence. This also means that the probability
of a device failing is not dependent on the non-failing time it
had before. (Here the "component life" comes in. It limits that
independence to a maximum non-failing operating time and says the
MTBF may become invalid what that is exceeded.)

When you actually want to measure MTBF, you run a number of devices
for a time until all have failed or the component life has
been exceeded (the latter usually done by statistical models
and/or accellerated ageing), count all non-failing hour you got
and divide them by the device number.

Now, this may be the wrong approach. It is quite possible that
device failure probability is not independent on the previous
non-failing operating time. In that case, one MTBF would not be the
right measure. Several different MTBFs could be given for
different periods of a devices lifetime so far as an approximation.
But this is not how it is done at this time. At this time
you get a failure probability per operating hour and the
only history of the device that goes into it is whether it
has already failed (and then all bets are off, it is assumed
to stay failed by the model) or whether it has exceeded its
component life time and the MTBF stated simply does
not apply anymore and is not replaced by any other value
instead.

Arno

"Mike Tomlinson" wrote in message ...
In article , Mike Tomlinson
writes

I'll take the board into work, remove the diode today and report back.

Took out the shorted diode today and the drive span up OK on a PC power
supply. Not yet tried it in the PVR but am sure it will be OK.

Thanks everyone for your suggestions.

PVR may have a crappy PSU with poor 12V regulation.