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Charlie Wilkes
Guest
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 Posted: Thu May 31, 2007 11:02 am Post subject: Weird modem problem |
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My situation is this:
I have a second residence where I use dialup to get on the Internet.
Today, I had trouble with my phone service... as sometimes happens,
after making a voice call, I had to unplug all phones and wait a few
minutes for the system to reset the dial tone. I don't know why this
happens.
After everything was working normally and I could get a dial tone, I
hooked up my computer and tried to dial... but I got a 'no dialtone'
message. So, I used a splitter to hook up a regular phone so I could
listen to what was going on.
The dial tone cut out when I plugged the rj11 cord into the laptop (SENS
LT56ADW Win Modem), and then came back when I unplugged it... This even
happened when the computer was totally powered down. Have I fried my
Win Modem? I don't think so because the Windows diagnostic can
communicate with it and does not detect a problem.
Fortunately, I happen to have a U.S. Robotics v.92 external serial port
modem on hand, and I had no problem using it to dial up a connection.
Does anyone know what might be going on here???
Thanks.
Charlie |
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Fred McKenzie
Guest
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| Posted: Thu May 31, 2007 9:14 pm Post subject: Re: Weird modem problem |
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In article <MPG.20c804a626150c80989685@news.easynews.com>,
Charlie Wilkes <charlie_wilkes@users.easynews.com> wrote:
| Quote: | The dial tone cut out when I plugged the rj11 cord into the laptop (SENS
LT56ADW Win Modem), and then came back when I unplugged it... This even
happened when the computer was totally powered down. Have I fried my
Win Modem? I don't think so because the Windows diagnostic can
communicate with it and does not detect a problem.
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Charlie-
There is probably some kind of transient absorber in the modem,
connected across the phone line. There might have been a voltage surge
(lightning strike a mile away?) that was more than the absorber could
handle. It protected your equipment, but now is a short circuit across
the phone line.
There may also be a reed relay that connects the phone line to the
modem. These relays normally do not handle much current, so anything
like a voltage surge might cause the contacts to stick in the off-hook
position. However that would not kill the dial-tone.
In other words you have a short circuit. If you can get to the circuit
components on the modem card, it is possible you can isolate the cause
and repair it.
Fred |
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Charlie Wilkes
Guest
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| Posted: Thu May 31, 2007 11:06 pm Post subject: Re: Weird modem problem |
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In article <fmmck-B78804.12144831052007@nntp.aioe.org>, fmmck@aol.com
says...
| Quote: | In article <MPG.20c804a626150c80989685@news.easynews.com>,
Charlie Wilkes <charlie_wilkes@users.easynews.com> wrote:
The dial tone cut out when I plugged the rj11 cord into the laptop (SENS
LT56ADW Win Modem), and then came back when I unplugged it... This even
happened when the computer was totally powered down. Have I fried my
Win Modem? I don't think so because the Windows diagnostic can
communicate with it and does not detect a problem.
Charlie-
There is probably some kind of transient absorber in the modem,
connected across the phone line. There might have been a voltage surge
(lightning strike a mile away?) that was more than the absorber could
handle. It protected your equipment, but now is a short circuit across
the phone line.
There may also be a reed relay that connects the phone line to the
modem. These relays normally do not handle much current, so anything
like a voltage surge might cause the contacts to stick in the off-hook
position. However that would not kill the dial-tone.
In other words you have a short circuit. If you can get to the circuit
components on the modem card, it is possible you can isolate the cause
and repair it.
Fred
Thanks. This squares with what happened yesterday. When I lost the |
dial tone as I described, I was attempting to test the line with a phone
that has an LCD display that is non-functional because it needs 3 AA
batteries, which I hadn't bothered to install.
What I heard was a repetitious clicking sound, and with each click, the
LCD display became visible for a moment... some kind of pulsing current.
The bottom line is that the *** phone company fried my internal Win
Modem. I think I'm gonna complain to the FCC, because this is not the
first problem I have had at this location.
Charlie |
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Floyd L. Davidson
Guest
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| Posted: Fri Jun 01, 2007 4:38 am Post subject: Re: Weird modem problem |
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Charlie Wilkes <charlie_wilkes@users.easynews.com> wrote:
| Quote: | What I heard was a repetitious clicking sound, and with each click, the
LCD display became visible for a moment... some kind of pulsing current.
The bottom line is that the *** phone company fried my internal Win
Modem. I think I'm gonna complain to the FCC, because this is not the
first problem I have had at this location.
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I don't see how you come to that conclusion. I doubt
the FCC would either, but regardless they will *not* be
interested anyway, as they have no jurisdiction over a
local telephone company.
Whatever, the LCD display would light up at a relatively
low voltage, and certainly would not survive any voltage
likely to damage a modem. You description of "some kind
of pulsing" sounds like regular dial pulsing of a
standard loop current, (which would be extremely loud if
you monitor it with anything that would provide a
"normal" volume for regular voice on a telephone line.
Whatever, that isn't the way that modems are damaged. A
surge from lightening can do it. So can a line that falls
across a 7200 volt power transmission line. But you don't
"hear" those...
--
Floyd L. Davidson <http://www.apaflo.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) floyd@apaflo.com |
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w_tom
Guest
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| Posted: Fri Jun 01, 2007 6:14 am Post subject: Re: Weird modem problem |
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On May 31, 2:06 pm, Charlie Wilkes <charlie_wil...@users.easynews.com>
wrote:
| Quote: | Thanks. This squares with what happened yesterday. When I lost the
dial tone as I described, I was attempting to test the line with a phone
that has an LCD display that is non-functional because it needs 3 AA
batteries, which I hadn't bothered to install.
What I heard was a repetitious clicking sound, and with each click, the
LCD display became visible for a moment... some kind of pulsing current.
The bottom line is that the *** phone company fried my internal Win
Modem. I think I'm gonna complain to the FCC, because this is not the
first problem I have had at this location.
|
How many actually fixed modems to learn what fails and why? Your
symptoms are classic of a common modem failure. First, phone lines
already have a 'whole house' protector installed free by the telco
where their wires meet yours. If you have provided that protector
with superior earthing, then surges on phone line would be earthed
long before geting to the modem.
Remember how electricity works. First a surge forms a complete
electrical path from cloud, through electronics, to earth. Then
current flows through everything in that path. Current does not flow
like a wave crashing on the beach. Current flows through everything
in that path simultaneously. Finally something in that path fails.
A typical path to earth ground is via wires taht are more exposed
and that don't have an earthed 'whole house' protector. Surges enters
on AC electric to pass through computer. Current exits via modem
(both an incoming and outgoing path must exist). Then to ground via
phone line.
What gets damaged? A common failure is a PNP transistor that drives
the modem's off-hook relay. If the PNP transistor is blown, then the
computer will respond with 'no dial tone detected' - never connect to
phone line. However if it was a lesser surge, then the transistor
may only short - always on. As long as computer powers modem, then
modem acts like a phone off the hook. Dial tone is lost - just like a
phone left off the hook. And again, computer would complain of 'no
dialtone detected'.
Telco did not do this damage. You are responsible for earthing
every utility wire to a common electrode before those wires enter the
building. That means your AC electric earthing must be upgraded to
meet and exceed post 1990 NEC requirements. That means every wire in
every utility cable must connect 'less than 10 feet' to that common
earthing electrode. Connection either via a protector (AC electric
and telephone), or via a direct hardwire connection (satellite dish
and Cable TV).
Remember, a protector is not protection. That telco provided 'whole
house' protector is only effective IF earthed 'less than 10 feet' to
same electrode used by AC electric and other utilities. If not, then
a surge may find earth ground, destructively, via your modem.
Some have posted "There is probably some kind of ..." IOW he is
guessing. This post is based on tracing surge damge by literally
replacing damaged parts soldered on circuit boards. If you let a
surge into your building, then it may find earth ground, destructively
via a PNP transistor and off-hook relay on that modem.
Most common source of damage to fax machines, modems, portable phone
base stations and answering machines: incoming on AC electric and
outgoing to earth ground via phone line (and the telco installed
protector). Damage directly traceable to surges that were not earthed
before entering a building. That incoming path can be anything
including cable and satellite dish. |
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Charlie Wilkes
Guest
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| Posted: Fri Jun 01, 2007 10:32 am Post subject: Re: Weird modem problem |
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In article <1180660446.788390.61630@x35g2000prf.googlegroups.com>,
w_tom1@usa.net says...
| Quote: |
Remember how electricity works. First a surge forms a complete
electrical path from cloud, through electronics, to earth. Then
current flows through everything in that path. Current does not flow
like a wave crashing on the beach. Current flows through everything
in that path simultaneously. Finally something in that path fails.
|
There haven't been any electrical storms recently. I'm in the Pac. NW
where they are fairly uncommon.
| Quote: | A typical path to earth ground is via wires taht are more exposed
and that don't have an earthed 'whole house' protector. Surges enters
on AC electric to pass through computer. Current exits via modem
(both an incoming and outgoing path must exist). Then to ground via
phone line.
|
This is a laptop, with a power cube that steps the voltage down and
converts it to DC. How likely is it that a surge of electricity would
make its way through the power cube, through the computer, and exit via
the modem and phone line without damaging something else besides the
modem? And what would the source of this power surge be?
| Quote: |
What gets damaged? A common failure is a PNP transistor that drives
the modem's off-hook relay. If the PNP transistor is blown, then the
computer will respond with 'no dial tone detected' - never connect to
phone line. However if it was a lesser surge, then the transistor
may only short - always on. As long as computer powers modem, then
modem acts like a phone off the hook. Dial tone is lost - just like a
phone left off the hook. And again, computer would complain of 'no
dialtone detected'.
|
It also acted like a phone off the hook when the power to the machine
was completely shut off. When I get back to my primary residence, I
will open up this laptop and try to determine the nature of the problem
and fix it if I can.
| Quote: |
Telco did not do this damage.
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Are you sure about that?
Charlie |
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w_tom
Guest
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| Posted: Sat Jun 02, 2007 12:08 am Post subject: Re: Weird modem problem |
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Stated was that a telephone line protector must be properly
earthed. Is your's installed and earthed? What is missing? Only way
to know is visual inspection. What must be may, instead, be missing.
Other sources of these transients include AC utility power
switching. We recently had a 33K wire drop onto a local primary
wire. That surge also that must be earthed before entering a
building. A surge that can overwhelm galvanic isolation inside the
power brick.
If a modem is hanging the phone line without power applied, then
either modem's relay is stuck closed or something else on modem's DAA
side has shorted. No power to create the problem means no PNP
transistor failure. Since power is not required to see it, then an
ohm (continuity) meter should locate the DAA (phone line) side short
immediately. Very few components are on that side of the board.
Also possible that a part has failed on its own - manufacturing
defects. If the 'free' telco protector is installed and earthed to
same ground as AC electric, then modem should never see more than 300
volts. 300 volts should not cause DAA damage. Is that telco
installed protector earthed to AC ground rod?
Best evidence is a dead body. Easy to discover what is shorting the
phone line since that failure exists even when modem is not powered.
On Jun 1, 1:32 am, Charlie Wilkes <charlie_wil...@users.easynews.com>
wrote:
| Quote: | There haven't been any electrical storms recently. I'm in the Pac. NW
where they are fairly uncommon.
...
This is a laptop, with a power cube that steps the voltage down and
converts it to DC. How likely is it that a surge of electricity would
make its way through the power cube, through the computer, and exit via
the modem and phone line without damaging something else besides the
modem? And what would the source of this power surge be?
...
It also acted like a phone off the hook when the power to the machine
was completely shut off. When I get back to my primary residence, I
will open up this laptop and try to determine the nature of the problem
and fix it if I can. |
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Fred McKenzie
Guest
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| Posted: Sun Jun 03, 2007 6:06 am Post subject: Re: Weird modem problem |
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In article <MPG.20c94f4c6b6a785b98968d@news.easynews.com>,
Charlie Wilkes <charlie_wilkes@users.easynews.com> wrote:
| Quote: | Telco did not do this damage.
Are you sure about that?
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Charlie-
If you measure voltage across the phone lines, it should be around 48
volts DC with the phone on-hook. The positive side may be grounded back
at the phone company's battery facility.
When your phone rings, the line has about a 90 volts AC, 20 Hz ringing
voltage. Therefore, your modem must be capable of withstanding these
voltages, plus a bit more to be sure it won't break down.
When the phone or modem goes off-hook, a small amount of current is
drawn from the line. That causes the phone company's equipment to turn
on the dial tone. If two phones or modems are off-hook at the same
time, you should still hear the dial tone but at a reduced level.
If you are listening to the dial tone on a phone, and it disappears when
the modem goes off-hook, then you either have a short-circuited modem
(which you might be able to measure with an Ohm meter), or a pulse was
generated on the line causing the dial tone generator to turn off (as if
you were dialing from a rotary phone).
If you measure the voltage on the line with a DC meter, a short circuit
in your modem would cause the voltage to go to near zero, compared to
several volts across the telephone when it is off-hook.
Fred |
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