Was helping out a friend this afternoon, troubleshooting their cable
internet connection when I stumbled upon another problem.. For some
reason, their comcast cable modem has gone out of whack, rebooting
itself constantly every two minutes or so. It boots up, initializes,
looks fine and then resets. Comcast is replacing it on monday.
While messing with the modem, I smelt a burning smell. I disconnected
the PC, opened the case, but saw nothing. It wasn't a strong smell,
but there was definitely a slight smell coming from somewhere. I also
checked the cable modem, but nothing there. Then, when I was
reconnecting the PC cables, I noticed the monitor's VGA cable was
burnt. The pins were fine, but that metal strip around the pins had a
hole burnt right through it.
Any idea what the cause could be? They do not have a surge protector,
just a couple of power strips. I'm wondering if there was some sort
of power surge that affected the cable modem and also caused this
problem. Not sure when the burn occurred, i do know that the cable
modem has been broken for about two days.
Nick wrote:
> Was helping out a friend this afternoon, troubleshooting their cable
> internet connection when I stumbled upon another problem.. For some
> reason, their comcast cable modem has gone out of whack, rebooting
> itself constantly every two minutes or so. It boots up, initializes,
> looks fine and then resets. Comcast is replacing it on monday.
>
> While messing with the modem, I smelt a burning smell. I disconnected
> the PC, opened the case, but saw nothing. It wasn't a strong smell,
> but there was definitely a slight smell coming from somewhere. I also
> checked the cable modem, but nothing there. Then, when I was
> reconnecting the PC cables, I noticed the monitor's VGA cable was
> burnt. The pins were fine, but that metal strip around the pins had a
> hole burnt right through it.
>
> Any idea what the cause could be? They do not have a surge protector,
> just a couple of power strips. I'm wondering if there was some sort
> of power surge that affected the cable modem and also caused this
> problem. Not sure when the burn occurred, i do know that the cable
> modem has been broken for about two days.
>
> Thanks in advance.
That took enough voltage to hurt someone or cause a fire!
HIGHLY recommend the computer be UNPLUGGED IMMEDIATELY until ALL THREE
conductors of the AC supply (on power strips AND at wall outlet) are
verified as being properly connected! It sounds like the ground of the
monitor or the computer might be connected to the AC instead of ground.
That COULD be what caused the cable modem to fail.
Computer peripherals plugged into different power strips doesn't sound
like a good idea either, especially if they are connected to different
outlets. WATCH out for counterfeit UL labels on power strips! All the
peripherals should be on the same surge protector as the computer. An
Uninteruptetable Power Supply is more that a power backup device, it is
a superior surge protection device than a surge suppressor.
Also make SURE the wires between the wall outlet and the power strips
aren't getting warm. Good idea to unplug the power strip and anything
else plugged into that outlet as well. In the US many home improvement
centers sell an inexpensive device that can determine if 120 volt AC
outlets are wired properly. The devices look like a grounded appliance
plug with three small lights where the wire would normally be. If one of
those devices shows ANY of the three conductors as disconnected or
reversed don't plug ANYTHING into the outlet until an electrician
corrects the problem. If a rental unit report the problem to local
building code enforcement if the landlord doesn't have miss wired
outlets corrected promptly.
A bad connection between the power meter and the neutral line on the
power grid can cause problems too. Sometimes the conductors of the
exterior power cable break due to corrosion after several decades,
leading to large voltage fluctuations, sometimes over-voltages, and
changes in electric lighting levels when things like refrigerators,
toasters or microwave ovens operate.
There are some areas in a CRT type monitor that have VERY HIGH voltages,
but I suspect that if those were connected to ground the fuse/circuit
breaker would blow or the monitor's solid state electronics would be
destroyed.
Thanks for the reply. These devices have been plugged in for over a
year with no problems. Any idea what would cause something like that
to happen all of a sudden? Regardless, I will advise them to switch
outlets for now and look into a surge protector.
Does the monitor need to be replaced because of the burn marks? Like
I said, the pins are all undamaged.
Nick wrote:
> Thanks for the reply. These devices have been plugged in for over a
> year with no problems. Any idea what would cause something like that
> to happen all of a sudden? Regardless, I will advise them to switch
> outlets for now and look into a surge protector.
>
> Does the monitor need to be replaced because of the burn marks? Like
> I said, the pins are all undamaged.
>
> Thanks again.
>
Advise them to get to the store to get one of those testers and use it
to test the outlet, then the power strips as soon as possible. Wouldn't
hurt to be at the store tomorrow when the staff unlocks the doors. They
aren't very expensive. However, THAT tester might not detect if the
whole household neutral has failed. If incandescent light brightness
changes when high load 120 volt devices like microwave ovens,
refrigerators, toasters; have the voltage tested with a volt meter. Be
particularly wary if lights get BRIGHTER when high load 120 volt
equipment operates. If the meter is able to detect over voltage in other
outlets when high load equipment operates have an electrician check
things out PROMPTLY. Sometimes different outlets in the same room are on
different circuits with 240 volts difference between the hot slot in one
outlet and the hot slot in another outlet! The electrical utility may be
responsible for repair material and labor costs if a fault is present
between the distribution grid and the utility meter.
Reversed wiring in outlets or power strips increases the possibility of
electrical shocks. Defeating the wide blade of two prong polarized plugs
or extension cords may lead to reversed hot and neutral conductors by
the time the electricity reaches the working equipment.
Might be a good idea to use a meter to verify there is NO electrical
potential (ZERO volts) between earth ground and the portions of the
computer equipment that are supposed to be grounded. These areas include
the computer case, the back panel of the computer and the outer shield
of the VGA cable connector.
Nick wrote:
> Thanks for the reply. These devices have been plugged in for over a
> year with no problems. Any idea what would cause something like that
> to happen all of a sudden? Regardless, I will advise them to switch
> outlets for now and look into a surge protector.
>
> Does the monitor need to be replaced because of the burn marks? Like
> I said, the pins are all undamaged.
>
> Thanks again.
>
Any chance of posting a picture ? There are image servers where
you can post a picture, and you could use one of those, if you
had access to a digital camera. Otherwise, explain in more detail
how it is burned. "Burned clean through" ? Scorched ? Marks of
some kind of arcing ?
The safest thing to do, is not use the items or their associated
power strips, until you've figured out where the marks came from.
A device like this can be used for testing wall outlets or an
outlet on the power strip. The plug in this picture, presumably
has a safety ground that cannot be seen by the camera angle used.
And a multimeter with a rating high enough to measure wall voltage,
can be used to verify the exact voltages present.
"Nick" <nmilot@gmail.com> wrote in message
news:1171165771.057707.257490@a75g2000cwd.googlegr oups.com...
> Was helping out a friend this afternoon, troubleshooting their cable
> internet connection when I stumbled upon another problem.. For some
> reason, their comcast cable modem has gone out of whack, rebooting
> itself constantly every two minutes or so. It boots up, initializes,
> looks fine and then resets. Comcast is replacing it on monday.
>
> While messing with the modem, I smelt a burning smell. I disconnected
> the PC, opened the case, but saw nothing. It wasn't a strong smell,
> but there was definitely a slight smell coming from somewhere. I also
> checked the cable modem, but nothing there. Then, when I was
> reconnecting the PC cables, I noticed the monitor's VGA cable was
> burnt. The pins were fine, but that metal strip around the pins had a
> hole burnt right through it.
<snip>
The monitor, the computer or *both* are not grounded properly...
and there must have been a power surge of some type (possibly lightning)
The house wiring needs to be checked at once to be sure the outlets are
grounded properly!
> Any chance of posting a picture ? There are image servers where
> you can post a picture, and you could use one of those, if you
> had access to a digital camera. Otherwise, explain in more detail
> how it is burned. "Burned clean through" ? Scorched ? Marks of
> some kind of arcing ?
Paul wrote:
> Nick wrote:
>> Thanks for the reply. These devices have been plugged in for over a
>> year with no problems. Any idea what would cause something like that
>> to happen all of a sudden? Regardless, I will advise them to switch
>> outlets for now and look into a surge protector.
> A device like this can be used for testing wall outlets or an
> outlet on the power strip. The plug in this picture, presumably
> has a safety ground that cannot be seen by the camera angle used.
> And a multimeter with a rating high enough to measure wall voltage,
> can be used to verify the exact voltages present.
>
> http://www.tequipment.net/ProductImages/AEMC/OT-1.jpg
>
> Paul
That's the type of tester I was recommending earlier. They do have a
ground prong. They are VERY simple, just three neon bulbs (with limiting
resistors) connected between the prongs. If ANY combination of lights
other than the TWO yellow ones illuminate when it is plugged in, there
is a problem with the outlet or its wiring.
Nick wrote:
>> Any chance of posting a picture ? There are image servers where
>> you can post a picture, and you could use one of those, if you
>> had access to a digital camera. Otherwise, explain in more detail
>> how it is burned. "Burned clean through" ? Scorched ? Marks of
>> some kind of arcing ?
>
> Here is a picture:
> http://img125.imageshack.us/img125/3969/p2110007nc5.jpg
>
That is weird looking.
That connector fits around the outside of the other connector.
The six "inward dimples", three on each side of the connector,
are there to give an interference fit to the shell. So the
shell has some retention force, even without the retention screws
being used.
It would make sense for one of the "inward dimples" to burn,
because the dimple is what makes electrical contact for the
ground (shield). What doesn't make sense, is why the outside
of the connector is burned. It almost looks like an arc was
struck, between the connector shell, and the metal fascia
of the computer. Which might suggest lightning or some other
transient effect. If the fault was continuous, you'd think the
plastic would melt.
I'd still try the outlet tester. If that kind of power
was involved, something elsewhere could have got
burned, like maybe the safety ground burned away etc.
The neon bulb outlet tester would be a start.
If the power strips had surge protection, you
might want to carefully disassemble the back of
the power strip (while unplugged of course) and see
if there are any bits and pieces of any protection
device that blew up. If so, discard the power strip.
The monitor connector can probably still be used - once
you've verified there isn't still a source of
danger in that setup. I've only dealt with a ground
fault once in the lab ( ~50V difference between instrument
grounds ) and I did get a shock. So be careful.
Burnt VGA connection. Cause? 
Linear Mode
