EBX board spontaneously resetting.

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Hey folks, I really hope someone can help shed some light on this
problem. It's driving me crazy and making me look pretty bad in front of
my client.

I have built an embedded PC based on an EBX motherboard. The model
number probably isn't important, but it's an Advantech PCM-9572 Celeron
400 MHz system with 128 MB of RAM and a 2.5" laptop hard drive. The
motherboard is fanless but I have a small fan blowing over the main
heatsink as extra insurance, since the system is run outdoors in 90
degree F heat.

I have now built two of these systems. In both cases they run rock solid
stable and undergo plenty of testing before being shipped. But
immediately  upon arrival to the customer, they are plugged in and begin
to spontaneously reset. Generally they don't even complete the booting
process, although sometimes they can get up and running for a few
minutes at a time.

When I received the first system back from the customer to diagnose the
problem, I found that if I loosened the mounting screws on the
motherboard and moved it around by barely millimeters, that I could get
the system to come up and stay up when it was in some sort of exact
"sweet spot". Any minor pressure applied outside of that position caused
a reboot.

The first time this happened I assumed it was a faulty mainboard and
obtained a new one. This one ran fine during initial testing and could
be moved around and even removed from the case without any problems. I
prepped the software install, ran more extensive tests and shipped the
system again, only to have the exact same problem show up, though it
took a couple of days for the symptoms to occur. It is now on its way
back to me.

Has anyone ever experienced this? Could it be heat issues? How can I
tell for sure? I doubt it is power surges because this system is run
with a lot of high end audio equipment and the users go through great
lengths to ensure they have clean power.

I really can't afford to send them another bad system. Suggestions on
similar motherboards would be helpful.

trena






Re: EBX board spontaneously resetting.
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The last time I had a problem like this I was using an industrial
PC enclosure in which the rear bracket was spaced too far behind the
motherboard by about 1/8".  When the PCI cards were pressed into
place and their mounting brackets nudged slightly to get the screwhole
aligned, it created a tension that tended to lift the card out
the motherboard socket after time and vibrations.

In general, when the gold card edge fingers are fully inserted into
the motherboard socket, the card bracket mounting slot must line up
perfectly with the screw hole and the top of the mounting bracket
must just touch the top of the rear enclosure bracket.  If not,
stresses will be introduced that can cause the card to eventually
work its way out.  Some enclosures are bad about this, and some are
even adjustable so alignment can be corrected.  In the situation
I mentioned earlier, it was necessary to shim the rear bracket
forward after drilling out the spot welds and replacing them
with screws.

This is just one possible explanation that seems relevant since
you reported the motherboard positioning was critical.  Also ensure
there are no vias or traces close to the motherboard mounting
holes that could be getting grounded by the brass standoff, and
use non-metallic washers on the screws.

TTaylor

Re: EBX board spontaneously resetting.
Hi Tom,

Thanks for taking the time to respond. I appreciate it.

Tom Taylor wrote:

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That's a good suggestion, but in my case I'm not using any expansion
cards. :(

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It seems to me that something is happening to the board in transit or
when it is being used in the client's environemnt, because before
shipping it did not exhibit any pickyness about grounding or placement.
Upon return, though, the symptoms arise.

Regards,

trena




Re: EBX board spontaneously resetting.

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Feels about right.  Which would mean you need to check your customer
just as thoroughly as you do your hardware, next time.  This may mean
you have to travel there and watch for yourself what they're doing to
that poor board...

--
Hans-Bernhard Broeker ( snipped-for-privacy@physik.rwth-aachen.de)
Even if all the snow were burnt, ashes would remain.

Re: EBX board spontaneously resetting.
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What you might try doing is to ship a board somewhere via the same carrier and
just have it shipped back, then test it. A company I worked for had a similar
problem although their product was much more complex. They would test it
thoroughly, then ship it, and the customer would report it as non-working. When
hand carried to the customer, the same type product would work. They redid the
manufacturing process and fixed the problem.

Re: EBX board spontaneously resetting.

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Try using insulated spacers on the motherboard. Also carefully inspect around
the screws that fix the motherboard to the present spacers with a monocle,
or some magnifying eyeglasses. Sometimes there may be a burr underneath
the screw head which may cut through the masking layer of the pcb and
create a short circuit to the chassis via the metallic spacers. Also check
around the spacer locations underneath the pcb with a magnifier. Some
problems may not manifest themselves until shipping to the client due
to vibration when transporting the system.


Re: EBX board spontaneously resetting.

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It's almost like you have the need for some power
isolation capacitors some where.  It would be interesting
to see if you could put your finger on the back of some
chip leads through mounting holes and also have it work.
Maybe you have noise that comes and goes with the
topology of your PC board where slight pressure makes
all the difference.



Re: EBX board spontaneously resetting.
Thanks, everyone, for the replies so far. I will have the EBX system
back probably Thursday or Friday, and I do intend to let the group know
what I find in the hopes it might help someone else in the future.

Regards,

trena




Re: EBX board spontaneously resetting.
Tom - thank you again for your response (and others too!). Your
suggestion to use insulating spacers between the screws and the board
led me to try using nylon screws, and believe it or not, the resetting
behavior has not repeated.

We got the system back on Wednesday, and it was immediately displaying
the resetting behavior consistently. Using nylon screws to hold the
motherboard appears to have done the trick. We have poked and prodded at
the board while it's running, shaken the system up (NOT while it's
running, :), run some CPU stress tests for hours to heat the board up
and it appears to be stable again.

Tomorrow we'll be able to test the first EBX board to see if using nylon
screws also removes the symptoms from that one.

Amazing how something so simple can make such a difference.

Regards,

trena





Re: EBX board spontaneously resetting.

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Why not while it's running?  We used to test mainframes for loose
connections and stray wire by raping on each card while the system was
running.  Of course you can use too much force but it took a fairly good
hit to do it right.

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--
    Gerald Bonnstetter
    Bonnsoft
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Re: EBX board spontaneously resetting.
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Another win for "Percussive Maintenance!"


Re: EBX board spontaneously resetting.
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You're quite welcome, trena.  Glad to be of help.

It appears that either 1) someone drilled out the original mounting
holes to make them larger and the side of the hole has reached the
inner power plane, 2) the PCB designer failed to allow an adequate
clearance ring in the internal power plane around the hole, 3) the
drilling machine or data table had an error that caused the hole centers
to be out of tolerance, or 4) a hole was drilled in a board location
that was never designed to have a hole.

In any case, your use of nylon screws should solve the problem.

Sincerely,

Tom Taylor

Re: EBX board spontaneously resetting.
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You really need to pin down the cause.  The nylon screw trick is
probably avoiding the problem for now, but without a pin something
else may rear its ugly head later.  Now you can tighten the
trouble source by selective use of the nylon in your shop, and you
will probably find that only one is needed.  Then you can check
the PCB for the above possibilities, or maybe something else.

--
"I'm a war president.  I make decisions here in the Oval Office
 in foreign policy matters with war on my mind." -         Bush.
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