PC keeps freezing when case bumped

[Dave]

I have a PC that freezes whenever it is bumped or knocked.

It absolutely freezes - no mouse movement, no keyboard response, no hard
disk activity... nothing.

Obviously the most likely case is a loose cable but I checked the cables and
removed and reseated the RAM and it hasn't improved the situation.

Anyone have any suggestions as to the likely cause? Could it be the
motherboard coming into contact with the case when bumped?

 

[Paul]

I have a PC that freezes whenever it is bumped or knocked.

It absolutely freezes - no mouse movement, no keyboard response, no hard
disk activity... nothing.

Obviously the most likely case is a loose cable but I checked the cables and
removed and reseated the RAM and it hasn't improved the situation.

Anyone have any suggestions as to the likely cause? Could it be the
motherboard coming into contact with the case when bumped?

You'll have to be your own detective in a case like this. I would
start by making note of where all the cables go inside the computer,
as part of preparation for disassembling it. (Note the cable colors,
like a red stripe on a ribbon cable marking pin 1, or note the wire
colors and orientation of connectors, in case you don't have good
documentation with the computer to help you with reassembly.)

The standoffs in some computers are made of brass (a conductor) and
it is part of the design that the brass standoffs come in contact with
tin plated round mountint holes on the bottom of the motherboard. They
are supposed to do that. The brass to tin connection is a ground, to
help reduce electrical interference. But the standoff should be well
centered with respect to the hole. If the motherboard is pushed to one
side, sometimes a standoff can touch something it is not supposed to.
In some cases, a user installs more standoffs under a motherboard, than
there are matching tin plated mounting holes on the bottom. If a standoff
is installed underneath a copper track, the standoff can short something.
(On one motherboard, putting a standoff in the wrong place, kills one
channel of the built in audio. So it does happen.)

Most of the rest of the connections in the computer should be designed
well enough, to not be affected by a bump.

The motherboard PCB can sometimes develop cracks or bad connections.
For example, a heatsink mounting method may place some of the solder
joints under stress on the CPU socket, and the solder joint can crack.
This means you can have an intermittent connection on the board. With
the computer running, you can (carefully) push on the surface of the
motherboard, and see if the computer freezes when the motherboard is
pushed.

Both kinds of faults can present the same symptoms. While completely
disassembling the system, and reassembling it again, can make the
problem go away, it may not tell you where exactly the problem is.
Finding a solution is not going to be an exact science.

At the factory, motherboards can be checked with a continuity checker
(bed-of-nails vacuum test jig), but there is no home-made equivalent
to that kind of test. It is much easier for the factory to find a
motherboard problem, than for a home user or even for a computer shop.
Returning the motherboard to the factory under warranty is the best
option if there is some evidence the fault is with the motherboard.

Paul

 

[Rod Speed]

I have a PC that freezes whenever it is bumped or knocked.

You're not supposed to kick it.

It absolutely freezes - no mouse movement, no keyboard response, no hard disk activity... nothing.

Obviously the most likely case is a loose cable but I checked the cables and removed and reseated
the RAM and it hasn't improved the situation.

Anyone have any suggestions as to the likely cause?

There's two main possibilitys.

The most likely one is that there is an intermittent short to case
and the bump produces the short. The best test for this possibility
is to run the motherboard loose on the desktop and see if bumping
the case still produces a freeze. If it does, its a faulty power supply
with a poor connection or cracked trace etc inside the power supply.

The other possibility is a cracked trace or bad joint on the motherboard
itself. You may be able to work that out by tapping gently on parts of the
motherboard with an insulated something to see if that produces the
freeze. Unfortunately the fix isnt that easy if it turns out to be that.

Could it be the motherboard coming into contact with the case when bumped?

Yes, that can certainly happen.

 

[paulmd]

I have a PC that freezes whenever it is bumped or knocked.

It absolutely freezes - no mouse movement, no keyboard response, no hard
disk activity... nothing.

Obviously the most likely case is a loose cable but I checked the cables and
removed and reseated the RAM and it hasn't improved the situation.

Anyone have any suggestions as to the likely cause? Could it be the
motherboard coming into contact with the case when bumped?

Pick it up and shake it (gently). Do you hear a rattle? If you do, it's
a screw trapped under the motherboard. Sometimes they get wedged in
there good, so you may have to remove the motherboard to get it out.


..

 

[kony]

I have a PC that freezes whenever it is bumped or knocked.

It absolutely freezes - no mouse movement, no keyboard response, no hard
disk activity... nothing.

Obviously the most likely case is a loose cable but I checked the cables and
removed and reseated the RAM and it hasn't improved the situation.

Anyone have any suggestions as to the likely cause? Could it be the
motherboard coming into contact with the case when bumped?

Examine everything, even unplugging and replugging parts,
also checking for good fit of power connector and cards,
that screws are tight on cards and motherboard.

 

[meow2222]

I have a PC that freezes whenever it is bumped or knocked.

It absolutely freezes - no mouse movement, no keyboard response, no hard
disk activity... nothing.

Obviously the most likely case is a loose cable but I checked the cables and
removed and reseated the RAM and it hasn't improved the situation.

Anyone have any suggestions as to the likely cause? Could it be the
motherboard coming into contact with the case when bumped?

One of those cases where one can say the possibilities are endless.
Somewhere there is a bad connection, either a poorly gripping socket, a
loose wire, a poor solder joint, a cracked track, a short, and it could
be almost anywhere. If you must fix it, take an insulated tool and prod
around to see what area is most sensitive to proddage. But unless you
need to fix it, I'd leave it alone for the simple reason that theres a
fair chance that once you find the problem it will stay stuck in
problem mode and you wont be able to fix it. IOW if its for home use
and it makes no diff whether its fixed now or later, later would be a
reasonable choice.

More to the point, a PC should never be bumped or knocked. It causes
HDD head slaps and damage, and kills HDDs.


NT

 

[Rod Speed]

Dave wrote

One of those cases where one can say the possibilities are endless.
Somewhere there is a bad connection, either a poorly gripping socket,
a loose wire, a poor solder joint, a cracked track, a short,

Or a loose screw floating around under the motherboard.

and it could be almost anywhere. If you must fix it, take an insulated
tool and prod around to see what area is most sensitive to proddage.
But unless you need to fix it, I'd leave it alone for the simple reason
that theres a fair chance that once you find the problem it will stay
stuck in problem mode and you wont be able to fix it.

It'd be worth trying the system with the motherboard
loose on the desktop too, that would at least eliminate
the possibility of a loose screw and that might be all it is
and would separate the motherboard from the power
supply. The power supply is cheap to replace if the
bad joint etc is in there instead of the motherboard.