[SI-LIST] Re: Strange resets happening in one of our circuit boards
- From: <istvan.novak@xxxxxxxxxxx>
- To: "Bashir, Shiraz (GE Healthcare)" <Shiraz.Bashir@xxxxxx>, istvan.novak@xxxxxxxxxxx, SI-List <si-list@xxxxxxxxxxxxx>
- Date: Thu, 01 Jun 2006 19:54:30 -0500 (CDT)
Was it possible to capture the shape of the +5/-3V noise on the reset signal?
How did it look like? Did it strictly correlate to when the chair was moved?
What is the bandwidth of the scope? Can it detect RF signal or is it in a
limited-bandwidth (like 20MHz) setting? When you moved the system from place
to place, was there something else moving with it? Maybe the emulator?
Regards,
Istvan
From: "Bashir, Shiraz (GE Healthcare)" <Shiraz.Bashir@xxxxxx>
Date: Thu Jun 01 19:27:45 CDT 2006
To: istvan.novak@xxxxxxxxxxx, SI-List <si-list@xxxxxxxxxxxxx>
Subject: [SI-LIST] Re: Strange resets happening in one of our circuit boards
I don't think so..we move unit from cube to engineering lab and another
test suite..
But very interesting thought though..you mean "movement of body" can
disturb standing wave and "direct" them to board..=20
Thanks,=20
Shiraz
-----Original Message-----
From: istvan.novak@xxxxxxxxxxx [mailto:istvan.novak@xxxxxxxxxxx]=20
Sent: Thursday, June 01, 2006 7:25 PM
To: Bashir, Shiraz (GE Healthcare); SI-List
Subject: Re: [SI-LIST] Strange resets happening in one of our circuit
boards
Shiraz,
Could it be that all this is happening in a strong electromagnetic field
so that a moving body nearby changes/moves the standing-wave pattern? Is
there any radio transmitter close by?
Regards,
Istvan
=20
From: "Bashir, Shiraz (GE Healthcare)" <Shiraz.Bashir@xxxxxx>
Date: Thu Jun 01 18:42:09 CDT 2006
To: SI-List <si-list@xxxxxxxxxxxxx>
Subject: [SI-LIST] Strange resets happening in one of our circuit boards
Hi,
A unit with microprocessor based system circuit board is resetting when
we plug in emulator port in JTAG port.
Using scope we see that CPU reset pin is asserted, hence the reset.
We see +5/-3V worth of noise on the signal just by rolling my chair back
and forth in front of the emulator.
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
OR
2. If we keep solder wires for scoping purposes.
It doesn't happen when Unit is enclosed in it's metal housing.
Investigated..
a. Reviewed schematics and CPU's reset line is pulled to 3.3V using 1K
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 which can drive reset too..but no issue
there.
D. Reset line is not going anywhere else other than JTAG port and Power
Monitor Chip
Brainstormed..
a. Soldering issue due to BGA ? Ruled out as how can soldering issue be
on three randomly selected units.
b. ESD- Ruled out as per our understanding ESD (air discharge) cannot
"arc over" from 2-3 feet distance.
Fix:=3D20
A team member recommended to put a capacitor across resistor. Did that
and problem went away.
Can anybody explain why it is happening ? Is it noise from Power Supply
but how can it defeat a strong pull up ?
Thanks,
Shiraz Bashir
General Electric Healthcare
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=20
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