Archived from groups: alt.comp.hardware.homebuilt (
More info?)
Start with voltage measurements from power supply. Even if
fans spin or lights light, the PSU can still output
insufficient voltage. Multimeter is essential. Voltage must
be within upper 3/4 limits for each voltage.
Assumed is that lightning enters via one port, damages
something, then stops. That is not how electricity was taught
even in elementary school science. To have electricity, it
must first travel through everything in a circuit -
simultaneously. What is the complete circuit into and out of
computer and cable modem? Begin there looking for damage.
First electricity flows through everything in a complete
circuit from cloud to earth. Only then does something(s)
fail. Now we are ready to find those something(s).
Parallel example: what is the path that typically damaged
POTS modems? Incoming on AC electric (the wires highest on
utility pole, most often struck, and that enter the house
typically with no 'whole house' protector). Incoming to
computer via a wire that bypasses power supply to make a
direct connection to modem. Outgoing via phone line that
connects to earth ground via the 'whole house' protector.
Yes, the telco typically installs a 'whole house' protector on
phone line for free. But AC electric is often the direct
connection to transistors from the cloud.
In your case, a direct connection would have been through
computer motherboard, through ethernet card, through cable
modem, to earth ground via the cable surge protection. Cable
requires no surge protector. It connects directly to surge
protection using a hardwire. Surge protection is the
building's single point earth ground. If cable was properly
earthed, then cable would have been the outgoing path - not
the incoming surge path.
As in the POTS modem example, usually a motherboard is not
damaged even through it conducts a transient into modem.
However little things can compromise that - meaning
motherboard PCI bus or a PCI slot may then be damaged. For
example, if motherboard is electrically connected to chassis
via multiple conductive standoffs, then a transient circuit
through motherboard could be destructive.
First strip system down to only motherboard, CPU, speaker,
and power supply. No Ram. No keyboard. No video controller.
And no AC power cable connected to PSU when doing changes.
When ready, reconnect power cable. Power up to both measure DC
voltages AND to listen for a speaker beep.
In the meantime, best to confirm the cable installation was
correct. No MOV (surge protector) is required for cable.
Surge protection is only required because cable can be earthed
directly (and less than 10 feet) to the single point ground.
This same earth ground as now required by post 1990 NEC must
be used also by the telco 'whole house' protector and by AC
electric. That earth ground with a 'less than 10 foot'
connection means cable and telephone have protection. Move on
to install a 'whole house' protector in AC mains breaker box
so that the most common reason for transistor damage is
eliminated.
Provided are how to trace out damaged components AND how to
avoid future damage.
Jack wrote:
> A neighbor had a lightening strike that took out his cable modem, and
> apparently struck his computer through his ethernet port. The power
> was hooked up to a surger suppressor. The ethernet was part of a riser
> that was built-in to the MB, too. I swapped out the PS and video card,
> and cleared the CMOS, after having stripped it down to bare bones (MB,
> processor, RAM, video card and speaker), and still not getting any
> POST or Beeps.
> I imagine the MB is toast. Didn't have a ram stick to swap that out,
> nor a processor, but I imagine it would be the MB.
> Any other thoughts?
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