[Shop-talk] blue screen problems... need the gurus

[John Innis]

I would think it depends a lot on the fan and what is powering that fan.
Modern CPU fans are all speed controlled, usually by a dedicated driver
chip.  Those chips are normally robust enough to withstand significant back
voltage without damage.  An increasing number of these fans are also
brushless.  As such, they develop much less voltage when spun up than a
standard DC motor would.  As long as there is no excitation voltage in the
field, they are not going to output much.  On the other hand it you have a
fixed speed Brushed DC motor case fan that is connected to the 5v rail of
the power supply you could generate significant voltage and apply it to
everything on that same 5v rail.

On Thu, Mar 31, 2016 at 10:43 AM, Tony Vaccaro <tvacc at lotusowners.com>
wrote:

>
>
>
>
> *From:* Shop-talk [mailto:shop-talk-bounces at autox.team.net] *On Behalf Of
> *John T. Blair
> *Sent:* Thursday, March 31, 2016 6:55 AM
> *To:* shop-talk <shop-talk at autox.team.net>
> While I see the logic in this, I have never had that thought. I have been
> working on computers for 35 years. Blown out hundreds of computers.
> Sometimes I block the fan, sometimes I don’t, but if I do it is only to not
> damage the fan and I just usually do it on Laptops as the fans are much
> more fragile.
>
>
>
> I have never had a computer fail to restart (which damaging the CPU would
> do) after blowing it out. My blower is super powerful and I used to use
> compressed air. I would spin those suckers right up.
>
>
>
> I would suspect there is a crowbar circuit in the CPU logic circuitry to
> prevent this from happening.
>
>
>
> I am not saying that this is not possible, just in all my years I have
> never seen it happen and I have seen most other computer related stuff
> happen. Not much I have missed.
>
>
>
> Tony V
>
>
>
> *Subject:* Re: [Shop-talk] blue screen problems... need the gurus
>
>
>
> At 10:01 PM 3/30/2016, Brian Kemp wrote:
>
> >John - You may have a dust problem.  Remove the power cord and open the
> >computer.  Take a shop vac that blows or some compressed air and clean
> things
> >out.  It is best to do this outside.
>
> John,
>
> If you blow down the inside of the computer with compressed air, put a
> finger on
> the fan on the CPU.  You don't want it to turn.  The compressed air can
> spin up
> the fan a lot faster than it is supposed to run.  So a DC motor being
> turned
> externally becomes a generator, and spinning faster then design speed
> causes it
> to output a higher voltage than it runs on.  This overvoltage is being
> applied back
> to the mother board and can back feed the CPU and cause it to fail.
>
> John
>
>
>
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