Electrical Engineering - Feedback destroying my computers...

Author

Feedback destroying my computers...

crispin.proctor@gmail.com

2007-08-14, 5:25 pm

Hi folks,

I've got an issue with my PC and some feedback that's going on which
is destroying my PC's. It's popped three mother boards already.

This is not really a computer related question so bare with me.

I have PC with a number of peripherals attached such as routers, USB
drives, active speakers etc.
Everything, barring the speakers, runs from it's own 12V PSU. Only
monitor is a switched PSU, everything else, old style. The speakers
have their own internal PSU which I would imagine is not a switched
flavour.

On the first occasion, I was connecting a USB drive, with it's own
external PSU, to the PCU and as the casing of the connector touched
the PC case, a spark jumped, not a small one mind you, nice and fat
and yellow, between the two. The PC fell silent. Motherboard was dead.

Second and third occasions, I was unplugging either the monitor or a
USB drive (Different one) and while I noticed no sparks, the PC fell
silent. Again, both times MB dead.

Now why would the be a PD between PC case and ground on USB drive?
Same for the monitor. The mains plug is correctly earthed and
everything is plugged into a strip plug.

This has happened in two different homes now. After the first
occasion, I replaced everything in the PC. Only "old" thing is the
case. All innards are new. As for the common devices between the first
and last occasion, only the monitor (External switched, 12V) and the
speakers are the same.

I get the lovely hum when I touch the speaker plug against the PC
case. Nice crackle to.

How can I go about tracing the culprit? Any easy way? Process of
elimination is difficult as I only have one monitor. The speakers I
could do without for a while.

Also, this seems to happen randomly. Not happened for 6 months now but
happened today. I can rule out (99% sure) static as the air is rather
humid and try as I might on the carpet, I get non. Also, the previous
attempt was on a wooden floor.

This is becoming expensive and frustrating now.

Thanks in advance for any pointers.

Regards,
Crispin

ChairmanOfTheBored

2007-08-14, 8:25 pm

On Tue, 14 Aug 2007 14:55:33 -0700, crispin.proctor@gmail.com wrote:

>Hi folks,
>
>I've got an issue with my PC and some feedback that's going on which
>is destroying my PC's. It's popped three mother boards already.
>
>This is not really a computer related question so bare with me.

Don Salad

2007-08-14, 8:25 pm

crispin.proctor@gmail.com wrote:
>
> I've got an issue with my PC and some feedback that's going on which
> is destroying my PC's. It's popped three mother boards already.
>
> This is not really a computer related question so bare with me.

Posting with NO PANTS is ALLOWED!

Thanks,
Don

Roy

2007-08-15, 3:25 am

This may sound foolish but:

Have you tried useing an Anti-Static Mat & Hand Brace before you touch
any part of your computers? you may inadvertantly been discharging
static electricity unto the equipment... it's one of the first things
they taught us in our computer repair lab class...It always seemed far
fetched to me too

but that is what this destruction of yours sounds
like to me.

Roy Q.T.
Urban Technician
[I don't make em, I just fix em]

Roy

2007-08-15, 3:25 am

If it's not static it must be Gremlins... invisible little gremlins.,
you'll have to go get help from your local sheriffs office =AE

David DeLaney

2007-08-15, 3:25 am

Don Salad <caesar@miskatonic.edu> wrote:
>crispin.proctor@gmail.com wrote:
>
>Posting with NO PANTS is ALLOWED!

Soldering with NO PANTS is also Allowed. But will probably produce better
stories.

Dave
--
\/David DeLaney posting from dbd@vic.com "It's not the pot that grows the flower
It's not the clock that slows the hour The definition's plain for anyone to see
Love is all it takes to make a family" - R&P. VISUALIZE HAPPYNET VRbeable<BLINK>
http://www.vic.com/~dbd/ - net.legends FAQ & Magic / I WUV you in all CAPS! --K.

Adrian C

2007-08-15, 9:25 am

crispin.proctor@gmail.com wrote:
> Hi folks,
>
> I've got an issue with my PC and some feedback that's going on which
> is destroying my PC's. It's popped three mother boards already.
>
1. Faulty mains supply lead / connector contacts, earth is open
2. Steel body of PC PSU is not connected to metal case (varnish?)
3. System connected to appliance with large Live-Earth leakage (TV?)
4. Monitor (remaining common component) has faulty inlet filters.

Or give up and buy a laptop :-)

--
Adrian C

daestrom

2007-08-15, 5:25 pm

<crispin.proctor@gmail.com> wrote in message
news:1187128533.855970.293680@o61g2000hsh.googlegroups.com...
> Hi folks,
>
> I've got an issue with my PC and some feedback that's going on which
> is destroying my PC's. It's popped three mother boards already.
>
> This is not really a computer related question so bare with me.

>
> I have PC with a number of peripherals attached such as routers, USB
> drives, active speakers etc.
> Everything, barring the speakers, runs from it's own 12V PSU. Only
> monitor is a switched PSU, everything else, old style. The speakers
> have their own internal PSU which I would imagine is not a switched
> flavour.
>
> On the first occasion, I was connecting a USB drive, with it's own
> external PSU, to the PCU and as the casing of the connector touched
> the PC case, a spark jumped, not a small one mind you, nice and fat
> and yellow, between the two. The PC fell silent. Motherboard was dead.
>
> Second and third occasions, I was unplugging either the monitor or a
> USB drive (Different one) and while I noticed no sparks, the PC fell
> silent. Again, both times MB dead.
>
> Now why would the be a PD between PC case and ground on USB drive?
> Same for the monitor. The mains plug is correctly earthed and
> everything is plugged into a strip plug.
>
> This has happened in two different homes now. After the first
> occasion, I replaced everything in the PC. Only "old" thing is the
> case. All innards are new. As for the common devices between the first
> and last occasion, only the monitor (External switched, 12V) and the
> speakers are the same.
>
> I get the lovely hum when I touch the speaker plug against the PC
> case. Nice crackle to.
>
> How can I go about tracing the culprit? Any easy way? Process of
> elimination is difficult as I only have one monitor. The speakers I
> could do without for a while.
>
> Also, this seems to happen randomly. Not happened for 6 months now but
> happened today. I can rule out (99% sure) static as the air is rather
> humid and try as I might on the carpet, I get non. Also, the previous
> attempt was on a wooden floor.
>
> This is becoming expensive and frustrating now.
>
> Thanks in advance for any pointers.
>

An idea that hasn't been mentioned yet is the 'grounding conductor' in your
wiring (the 'third prong'). If the outlets are mis-wired you may have a
voltage on the third prong and that would put a voltage on the frame of some
of your equipment. Even worse would be if one outlet has this problem and
another outlet doesn't. So connecting a USB device powered from one outlet
to the USB port on the computer, when the 'metal frame' of one touches the
other you would short the stray voltage from the mis-wired outlet to ground
through the correctly-wired outlet.

If you are 'handy' with a multi-meter, measure the voltage between the
ground prong of several outlets (from the ground prong of your PC outlet to
the ground prong of several other outlets). If you find any voltage at all,
there is something wrong. These 'grounding conductors' should not normally
carry any current and should all be connected to the same bus inside the
service panel.

One way this could be mis-wired is to not have a ground wire back to the
service panel and instead just a jumper between the third-prong screw and
the neutral conductor. That would put a couple of volts on the third-prong
(whatever voltage drop there is along the neutral conductor when loaded).

daestrom

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