rp wrote:
On Fri, 11 May 2018 06:53:14 -0000 (UTC), Yes wrote:
I followed your advice. I have four SATA devices - a CD/DVD player and
three HDDs. I disconnected all of them. The pc booted up. After
that, I re-connected each one individually. When all was said and
done, one HD would always result in immediate shutdown. With another
HD, the pc would boot up, but BIOS would not recognize that the HD was
there. My pc would only recognize the CD/DVD player and one HD.
Fortunately (???), that was my c: drive. I'll have to research if the
data on the broken HDDs can be salvaged.
I believe the SATA connectors on the mobo work. I plugged the SATA
cable of the working HD into the various SATA connectors and confirmed
that BIOS recognized it.
I'm glad it helped. More often than not it's a drive problem but that's
just in my experience and someone else may have seen more motherboard
problems :-)
It does sound as if you have two faulty drives. Maybe switching the
power off and on too quickly caused a spike that killed them. It
shouldn't happen with any power supply but maybe a budget one couldn't
cope with the frequent off and ons. If it's a quality supply that's
done it I'd replace it as I would take that as a sign of future trouble
looming.
You can actually burn the TVS diodes on a hard drive,
if the power supply overvoltage lasts long enough.
https://community.wd.com/t/hdd-tvs-diode-faq/14692
Unfortunately, modern hard drive circuit boards are
turned component-side-in so you cannot see the diodes.
Older drives, you could see the TVS diodes near the power
inlet point on the drive. I didn't know these existed
at first, until someone posted that they had a hard
drive problem and "what are these two burned things".
And that kicked off my first search for what those
might be. The person who posted, came up with the
theory, and I could find mention of those on the web.
They exist to support hot plugging. Even IDE drives
have been loaded into trays for hot insertion (with
the right circuit design), and to protect the drive
from power transients (inductive kick because
hard drive motor +12V is still flowing), the TVS
clips the tops off any inductive spikes. That's what
it's supposed to do. If a power supply overvolts
for a long period of time, those TVS burn. The TVS
don't do well in the presence of a supply failure.
*******
A power supply should not overvolt like that and
I would replace it immediately.
There is a certain model of Bestec supply which is
famous for overvolting. It was used on Emachines.
When the supply failed, it would destroy all the
storage on the computer. That's because at least
one rail would go too high. Things like the CPU
and the RAM would be OK, because they're protected
by onboard regulation.
*******
The power supply has an "inrush limiter".
http://www.pavouk.org/hw/en_atxps.html
It's NTCR1 in the upper left corner. It needs to
cool off, to return to a high-resistance state.
The next time you turn on the supply (at the back),
NTCR1 forms an RC circuit to limit the charging rate
of the main caps (C5/C6). When NTCR1 warms up, it
stays in a low resistance state (negative temperature
coefficient).
To treat that device well, if you turn off the supply
at the back, wait at least 30 seconds before turning
on again. That's to give NTCR1 a chance to cool off,
and get ready for the next "inrush". The inrush current
can be on the order of 40 amps, so it's no joke.
(The value is printed in some spec sheets.)
On modern supplies, some of them use the Active PFC
circuit as an inrush limiter, so NTCR1 is no longer
required.
But that component has nothing to do with "overvolting
behavior". And even if you kill the power at the back,
the main caps (C5/C6) provide "hold-up time". You would
have to hammer the switch on the back, as the rails were
falling or something. You would need to be a "merciless
switch puncher" to manage to damage stuff. Um, don't
do that.
One other dude already learned this lesson. He posted
"I hit the switch on the back, like 50 times, and
something blew". Yes, something can blow.
Paul