PC reboots if someone walk by

[churin]

PC reboots if someone walks by

My PC reboots if someone walks by the machine or if I touch the metal part of eSATA or USB connector(not connector contacts). It appear to have something to do with electrostatic discharge. I am using AC power connector having three pins. This never happened with my old machine.
Any suggestion for possible remedy is appreciated.

 

[FuturDreamz]

yeah seems like the computer is not grounded properly.

 

[churin]

The mobo is electrically connected to the chassis because it is fastened to the stand-offs by screws. Do you mean this is the cause of my problem? What I am suspecting is the opposite: The mobo is not electrically connected to the chassis. But I do not see how.

 

[churin]

The pictures as attached below show the areas of the mobo where the stand-off or the screw touches. It indicates that the ground plane of the mobo will be electrically conductive to the stand-off and thus to the chassis.

 

[churin]

The pictures as attached below show the areas of the mobo where the stand-off or the screw touches. It indicates that the ground plane of the mobo will be electrically conductive to the stand-off and thus to the chassis.

the hole there with the metal around it is most likely not one of you standoff holes. if it is you should have received paper washer with your case to be placed between the mobo and the stand off.

The hole is one of the eight holes to be used for ATX mobo. I reviewed what came with the mobo or the case and found no washer(metal nor insulation) in it. I assembled PC many times in the past and mobo always looked like this. I once used metal washer but never seen insulation washer to be used on mobo.
You indicates that the mobo's ground plane should not be conductive to the chassis through the stand-offs. I believe that for making the system more tolerant of electrostatic interference. But the mobo does not appear to be designed that way.

 

[Fumz]

The pictures as attached below show the areas of the mobo where the stand-off or the screw touches. It indicates that the ground plane of the mobo will be electrically conductive to the stand-off and thus to the chassis.

the hole there with the metal around it is most likely not one of you standoff holes. if it is you should have received paper washer with your case to be placed between the mobo and the stand off.

The hole is one of the eight holes to be used for ATX mobo. I reviewed what came with the mobo or the case and found no washer(metal nor insulation) in it. I assembled PC many times in the past and mobo always looked like this. I once used metal washer but never seen insulation washer to be used on mobo.
You indicates that the mobo's ground plane should not be conductive to the chassis through the stand-offs. I believe that for making the system more tolerant of electrostatic interference. But the mobo does not appear to be designed that way.

There are 10 "holes" in an ATX motherboard that fit into corresponding standoffs... each is lined as your picture above indicates. However, this metal lining is there to protect the motherboard's PCB from carelessness, not to conduct electricity.

It's possible that you may have placed a standoff behind the board where you should not have; although, since you also have an ATX case, this is very unlikely. Nevertheless, it's possible because not every case is well made.

Which brings us to my $0.02: the case may be shorting out, through no fault of your own. Just about the same thing happened to a friend of mine who decided to go cheap on his case. It was cheaper to RMA it for another model than it would have been to have it wired properly.

If the case isn't new, then I'd say to double, then triple check your wiring... because that's really the only new variable.

 

[Dwarf]

The pictures as attached below show the areas of the mobo where the stand-off or the screw touches. It indicates that the ground plane of the mobo will be electrically conductive to the stand-off and thus to the chassis.

That is correct. Those are the mounting points of the motherboard, and they are designed that way so that when they are correctly mounted in the case (or on the motherboard tray if your case has one of those), they are all electrically connected together thereby creating a shield. It is important that they are all correctly mounted because the motherboard is designed in this way. Referring to your image, the mounting point appears at first glimpse to be electrically isolated. However, don't forget that modern motherboards are not just double-sided but that they are multi-layered, so these mounting points are also electrically connected to the inner layers. Note that not all of these points will be electrically connected to the circuitry on the motherboard as this depends on the motherboard design. Some are, some aren't.

The other holes (those without a ring of solder) are not mounting holes for the motherboard/chassis, but are for attaching the processor heatsink assembly (when located round the processor socket). Elsewhere, they will be due to the manufacturing process of the motherboard (reference points to aid alignment of the layers).

 

[churin]

Staple Head and Fumz:
Thank you for your responses. Please misunderstand me. I am simply stating my observation which may be wrong. If so please correct me. I know there must be something wrong somewhere.
I checked by using a circuit tester the conductivity between the metal area around the mounting hole and other area on the mobo. The result is that the mounting hole area is NOT electrically isolated on the mobo or it is electrically conductive to ground plane of the mobo to which minus pin of the 24 pin power supply connector, metal enclosures of the USB connectors, the audio connectors, etc. are conductive.
It appears to me that using insulation(non-metalic) stand-offs is the only way to avoid electrical contact between the mounting holes and the chassis through the stand-offs.

 

[Thorsen]

maybe its the PSU itself, maybe a connection is loose inside or a wire touching another wire?

 

[churin]

The other holes (those without a ring of solder) are not mounting holes for the motherboard/chassis, but are for attaching the processor heatsink assembly (when located round the processor socket). Elsewhere, they will be due to the manufacturing process of the motherboard (reference points to aid alignment of the layers).

The two pictures show top and bottom side views of the same hole.

 

[Dwarf]

Those mounting points are designed to be electrically connected to the chassis, hence the ring of solder to ensure a good contact with the mounting screws.

This does seem to be a strange problem, and it would seem to point to a grounding issue. Ensure that your motherboard is correctly mounted, following my advice about mounting points and screws. Check for electrical conductivity between the chassis and the earth terminal on the PSU socket. Plug the mains lead in (do not connect to the supply) and check that you have conductivity between the chassis and the earth connection in the plug. If not, check the mains lead for conductivity on the earth lead. Repair/replace if a fault is found. If you find no fault, then it might be a fault on your house wiring GET THIS CHECKED BY A PROFESSIONAL. If you have radiators in your room, then connect a wire between the chassis of your computer to the pipework of the radiators in order to provide a ground connection. Ensure that this connection is made to bare metal.

 

[Darryl Licht]

Somethig to look at... some PSU's have a ground wire, some dont. Does yours? If so is it attached and properly grounded?

I have built hundreds of PC's over the last 17 years, usually problems like this are due to a loose nut behind the screwdriver! That is, it may be an electrical connector on the mobo not plugged in all the way, or improperly... a bent pin touching another, basically you may have missed or overlooked something.

Double and triple check every single connection, every pin, the front panel connections, usb, etc. Also look at the IO shield at the back of the PC, make sure one of the little metal "fingers" isnt grounding out a USB or Firewire connector.

 

[churin]

As a trouble shooting measure, I unplugged the reset cable and am waiting to see if the problem goes away. I have to wait for a day at least to determine if that will stop recurring the rebooting. I will post back.

 

[Darryl Licht]

Please keep us informed of your progress...

 

[churin]

Please keep us informed of your progress...

I have determined that unplugging the reset cable from the header on the mobo prevents the rebooting.
Now I have plugged a reset cable on the header. The cable is not the one which is built in the case but a loose cable with a switch fitted on one end and a plug connector on the other end.
I will post back.

 

[Darryl Licht]

Sounds like you may have a bad reset micro switch!

Glad to help you out!

Now you can get to enjoying Win7!

 

[churin]

Sounds like you may have a bad reset micro switch!

Glad to help you out!

Now you can get to enjoying Win7!

Unfortunately not quite yet!
The resetting does not happen if the length of the cable for the reset switch is one inch but if it is 12 inches the problem(resetting) comes back. I am testing by inducing electrostatic charge in my body and discharging it by touching outer surface of the case.
I am beginning to think that I have to settle with having no reset switch or else ditch the case and pick a different one.
Attached are pictures of the machine:

 

[Darryl Licht]

Sounds like you may have a bad reset micro switch!

Glad to help you out!

Now you can get to enjoying Win7!

Unfortunately not quite yet!
The resetting does not happen if the length of the cable for the reset switch is one inch but if it is 12 inches the problem(resetting) comes back. I am testing by inducing electrostatic charge in my body and discharging it by touching outer surface of the case.
I am beginning to think that I have to settle with having no reset switch or else ditch the case and pick a different one.
Attached are pictures of the machine:

What case? contact the manufacturer... tell them you have a bad rest switch or wire harness... they should send you a new one. How old is case?

 

[Dwarf]

A very strange one indeed. I am pleased that you have managed to narrow down the problem. What I think is happening, particularly when you say that a very short cable doesn't exhibit this phenomenom but a longer one does, is that the cable is acting like an aerial and picking up this charge somehow and causing the reset of your system. What I suggest is that you manually shield this cable by wrapping it in another wire which you connect to a good earthing point on your chassis. Try re-routing this cable away from the rest of the cables, particularly the PSU power harnesses.

Another test that you can do involves your PSU, or more specifically a certain connection. With reference to the following illustration, use a multimeter to back-probe the PWR_OK line on the main 20/24 pin ATX power connector. The connector pin numbers are 7 (black, COM) and 8 (gray, PWR_OK).



With the meter connected, power up your system. Note that the voltage shown must lie within the range 2.4V to 6.0V, with a nominal value of 5.0V. Now, do what you have done before to reset your system by electro-static discharge. What happens to the voltage on the meter? If it falls below the 2.4V threshold (or, in rare occasions, rises above the 6.0V threshold) then you are suffering what is known as a brownout where the PSU fails to maintain the correct power output. This causes a timer chip on the motherboard to hold the reset line to the processor, thus preventing it from running under bad or unstable power conditions. When this voltage returns to its correct level, the reset line is released and the processor resumes operating, effectively beginning operation as if you had just powered the system on.

Again, referring to the illustration, there is another test. This involves the PS_ON# line. Connect your multimeter to the following pins on the connector: 15 (black, COM) and 16 (green, PS_ON#) or pins 13 (black, COM) and 14 (green, PS_ON#) depending on whether you have a 20-pin or a 24-pin connector. For normal running mode, this should show a reading of <2.0V. Again, reset your system by the electro-static discharge method. What happens to the reading here? If it becomes >2.0V, then the PSU voltages are disabled, effectively powering down the system.

Consequently, it may be prudent to check the main power switch as well as what you have already found out with the reset switch and, as I suggested, manually shield the cables and route them away from the rest of the cables, in particular the PSU power harnesses.

 

[churin]

Dwarf,
Thanks for your detailed suggestion.
I thought about shielding the reset cable and tried that but it did not solve the problem.
A lot of cables are run between the mobo and the front panel as shown below picture. I unplugged the audio, USB and eSATA cables from the mobo, and shielded reset, pwr and LED cables together by wrapping them by aluminum foil and grounded using a copper wire to one of the nine screws nearby. But no dice. I unplugged the reset cable from the mobo, then the resetting did not happen. Previous experiment indicated that the resetting does not occur even the rest of the cables from the front panel are connected to the mobo as long as the reset cable is unplugged.

Regarding your suggestion about checking voltage using circuit tester, is this for checking PSU if it is functioning normally or not?
I did functional test by putting all parts together on a table without using the case. It worked fine and I could install W7. At that time cable length of one inch each for the reset switch and pwr switch were used. I sometimes felt spark lightening happening when I touched the pwr or reset switch but it did not bother the system.

All those cables(reset, pwr, usb, eSata, LED, audio) are tightly bundled together which was done by vendor of the case. The main power supply cable is running reasonably away from the rest of the cable harness.