boot sector f*ed
nightrecon at hotmail.com
Thu Aug 13 09:39:49 UTC 2009
Roland Smith wrote:
> - Powersupply: check the voltages (preferably under load) with a
> monitoring app like mbmon. If that's not possible, check in the BIOS. A
> failing powersupply can give weird unreproducable errors. If you have
> ever heard a popping noise from the machine it could be a short in the
> powersupply caused by dust. I've seen that fry motherboards.
A marginal to beginning to fail power supply will have more ripple when
under heavy load. In the earliest stages it may only manifest when load is
extremely heavy, but as time wears on it will get worse. You would have to
be looking at it with an oscilloscope to see this. A simple voltage check
with something like a VOM that averages power may show voltages within the
correct range, but is totally blind to the filtering quality (ripple).
It can also account for very weird behaviors. At boot time the current
required to spin up the drive is huge relative to the current used during
normal operation. If the power supply is only marginal it may only be
slipping out of spec during this period and seem to be fine the rest of the
time. Easiest way to eliminate is to simply substitute a known good from a
working machine that has at least the minimum wattage needed.
An example: A WD800JB takes 2.2 amps on the 12 volt rail to spin up, but
during normal ops read/write/idle is 350ma with seek being 900ma. The 5 volt
rail will use 525ma on spin up, read/write/idle is 800ma with seek at
675 ma. A lot of slightly earlier generations of drives used 2.5 amps or
more. Easy to see the 12 volt rail being insufficient wattage and/or out of
spec ripple-wise can be a problem. A lot of older cheap power supplies on
the market do not have a lot of capacity on the 12 volt rail.
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