[ale] computers sometimes befuddle me

[Michael H. Warfield]

On Fri, 2013-01-18 at 16:42 -0500, Calvin Harrigan wrote:
> Could be that the fan was shorted?  Killing the 5V supply in that area 
> of the board?  Where you getting a POST beep?

Those fans usually run on 12V (yes, there are exceptions).  Especially
the larger chassis fans and even the CPU and GPU fans (some laptops have
5V fans).  You wouldn't typically want them on your more sensitive 5V
rails where they would draw more than double (2.4X) the current and
potentially introduce motor noise on that bus.

When I run into an anomaly like that, I would do something like plugging
the fan back in and confirming it was the cause rather than assuming.
It could be equally possible that it was thermal and the temperature
fluctuations of powering it down and back up again could have triggered
it.  I've had more than one computer that had been running hot for
months (or more) without batting an eyelash but, when turn off, would
not power up from a "cold" state.  Let it warm up with power on those
rails (dead as it were) and then reset it and up it comes.  Those sorts
of problems are USUALLY in socketed chips but not always.

My favorite story in that regard relates back to Hayes Microcomputer
Products days back when I was married to my first wife, Julie, and she
was one of their lead techs.  They were having chronic problems with
their new 9600 baud modems (damn, we've come a long way baby) where they
would eventually start to fail after months of service.

She had given me an early production model for my birthday one year.
Mine eventually failed but I figured out why.  She had told me about the
problems they were being plagued with.

It had two connected boards, one upside down.  The upside down one had a
big square socketed, edge contact (leadless), chip AND it had cut
corners on all four corners of the socket (meaning each side was not
connected to the other sides other than through the base and could flex)
so you could use a chip-lifter to pull the chip.  When I took my modem
apart and pressed firmly on that chip and heard a nice satisfying SNAP!
Modem worked after that.  I told her that it was bad socket design and
that thermal cycling would cause the upside down chip to walk its way
out of the socket.  They needed solid corner sockets with positive
retention.  She relayed the word up to the engineers and they fixed the
problem and she got a bonus.  Case closed.

DIP (Dual In-line Package) chips use to (still have) have similar
problems in sockets.  From the supplier, the legs bend outwards
slightly.  That's for the machines that insert them.  The legs act like
little springs that hold them in place in the machines until inserted.
But...  That same spring action causes them to walk out of DIP sockets
over time (years).  Old service man magic was, when a machine started
acting flaky, to take a board and press all the socketed chips back into
their sockets or even take the chips out, square the leads, and
reinsert.  9 times out of 10 that resurrected the balking machine.

Same thing happens with boards and board edge connectors.

Regards,
Mike

> On 1/18/2013 4:35 PM, Sean Kilpatrick wrote:
> > I was doing routine maintenance -- cleaning out dust bunnies.
> >
> > Also wanted to isolate which fan was rattling on startup. It turns out
> > the extra case fan is making the noise -- noise goes away after 2-3
> > minutes of up time.
> >
> > Finish the cleaning, close the case, and turn on the power: get beep
> > code indicating no video. WTF
> >
> > Open up the case and try reseating the video card (mobo video ports have
> > died.) No help.
> >
> > Changed video cables. No help.
> >
> > Plugged my netbook into the big monitor. Monitor works. (little ARM
> > netbook is working as hard as it can to drive the larger monitor at full
> > resolution, so browser is slowed to a crawl, but it does work.)
> >
> > Finally, while I am sitting on the floor scratching my whatever, I pull
> > the internal power plug to the noisy fan. On powerup video works again.
> >
> > WTF!
> >
> > Sean
> >
> >
> >
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-- 
Michael H. Warfield (AI4NB) | (770) 985-6132 |  mhw at WittsEnd.com
   /\/\|=mhw=|\/\/          | (678) 463-0932 |  http://www.wittsend.com/mhw/
   NIC whois: MHW9          | An optimist believes we live in the best of all
 PGP Key: 0x674627FF        | possible worlds.  A pessimist is sure of it!
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