[SI-LIST] Re: Strange resets happening in one of our circuit boards
- From: "Grasso, Charles" <Charles.Grasso@xxxxxxxxxxxx>
- To: <doug@xxxxxxxxxx>, <stubenner@xxxxxxxx>
- Date: Fri, 2 Jun 2006 11:01:01 -0600
Hi Doug,
Excellent point! You may also recall some excellent research done by
(if memory serves) a Unisys scientist. He was called into a computer
room that was experiencing random resets of their computer terminals.
He discovered that the source was ESD events caused by the operators
scooting across the tiled floor on their chairs and colliding with=20
metal cabinets. He simulated the events with two metal balls in a
velvet lined box - he measured low voltages with extremely fast edges.
Again - if memory serves - the bandwidth of the event exceeded 10GHz!
Best Regards
Charles Grasso
Senior Compliance Engineer
Echostar Communications Corp.
Tel: 303-706-5467
Fax: 303-799-6222
Cell: 303-204-2974
Pager/Short Message: 3032042974@xxxxxxxx
Email: charles.grasso@xxxxxxxxxxxx;
Email Alternate: chasgrasso@xxxxxxxx
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of Doug Smith
Sent: Thursday, June 01, 2006 10:05 PM
To: stubenner@xxxxxxxx
Cc: Shiraz.Bashir@xxxxxx; 'SI-List'
Subject: [SI-LIST] Re: Strange resets happening in one of our circuit
boards
Hi All,
I may not have mad it clear in my first posting on this subject. The=20
sparking occurs between pieces of unconnected metal within the chair=20
as the cushion returns to its normal shape after standing up (takes=20
longer for some of us than others). You do not see or hear sparking=20
but it is occurring and is multiple events.
Doug
stubenner@xxxxxxxx wrote:
> Shiraz,
>=20
> This doesn't sound very strange at all, and it probably is a good =3D
> question
> for Doug to field, but I'll throw in my two cents-worth.
>=20
> You prematurely ruled-out ESD. It may be true that your problem is not
a
> direct discharge ("arc") to your circuit, however, any discharge also
> launches a broadband EM signal as well - just like a lightning strike.
=3D
> This
> signal, I'll assume it's a radiated-only issue at this point, can be =
=3D
> coupled
> into conductors connected to your circuit and you may see the sort of
> problem that you are experiencing.
>=20
> The chair ESD discharge issue pops up a lot. Years ago I had a similar
> problem where the chair was discharging to a desk over 20 feet from
some
> electronic test equipment and it caused the equipment to malfunction.
>=20
> Regards,
> Stu Benner
> EMConsulting
> www.emcwizard.com
>=20
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx] =3D
> On
> Behalf Of Bashir, Shiraz (GE Healthcare)
> Sent: Thursday, June 01, 2006 7:42 PM
> To: SI-List
> Subject: [SI-LIST] Strange resets happening in one of our circuit
boards
>=20
>=20
> Hi,
> A unit with microprocessor based system circuit board is resetting
when =3D
> we
> plug in emulator port in JTAG port. Using scope we see that CPU reset
=3D
> pin is
> asserted, hence the reset. We see +5/-3V worth of noise on the signal
=3D
> just
> by rolling my chair back and forth in front of the emulator.
>=20
> This happens in following scenario:
> 1. User is sitting on chair, user gets up (doesn't touches the
> unit) and unit resets.
> We demonstrated this on three randomly selected units.
Sounds
> ridiculous but it is true
>=20
> OR
>=20
> 2. If we keep solder wires for scoping purposes.
>=20
> It doesn't happen when Unit is enclosed in it's metal housing.
>=20
> Investigated..
> a. Reviewed schematics and CPU's reset line is pulled to 3.3V using 1K
=3D
> ohm
> resistor. b. Physically checked that pull up resistor is in place and
is
> connected with BGA ball of reset pin. c. We checked power monitor chip
=3D
> which
> can drive reset too..but no issue there. D. Reset line is not going =
=3D
> anywhere
> else other than JTAG port and Power Monitor Chip
>=20
> Brainstormed..
> a. Soldering issue due to BGA ? Ruled out as how can soldering issue
be =3D
> on
> three randomly selected units. b. ESD- Ruled out as per our =3D
> understanding
> ESD (air discharge) cannot "arc over" from 2-3 feet distance.
>=20
> Fix:=3D3D20
> A team member recommended to put a capacitor across resistor. Did that
=3D
> and
> problem went away.
>=20
> Can anybody explain why it is happening ? Is it noise from Power
Supply =3D
> but
> how can it defeat a strong pull up ?
>=20
> Thanks,
> Shiraz Bashir
> General Electric Healthcare
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--=20
------------------------------------------------------------
___ _ Doug Smith
\ / ) P.O. Box 1457
=3D=3D=3D=3D=3D=3D=3D=3D=3D Los Gatos, CA =
95031-1457
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