Modem won't hang up any more!

  • Thread starter Thread starter Chief Thracian
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Chief Thracian

alt.comp.hardware, alt.comp.periphs

As of two weeks ago, I can no longer Internet-connect
the usual way, via my Supra Express 56k modem. (My OS
is Windoze98.) Here's the problem:

I need to unplug and replug the telephone line going to
the modem, to restore the dial tone. If not, the phone
line remains open, so I can't receive or send phone
calls. It's as if the modem lost its ability to hang
up. (Problem remains even when my computer is shut
down...so I know it's not OS--or even
computer--related.)

Now, when I don't need to get on the 'net, I unplug the
phone line from the modem, and plug it into the back of
my answering machine... which then allows me to receive
and make regular phone calls.

Is this a burnt-out modem chip? Or can I possibly
restore my modem to its former excellent condition?
Where do I start? I have yet to find the appropriate
help file. If you know of one, please direct me to it.
Otherwise, I'd much appreciate someone guiding me
through possible maneuvers to correct the error.

TIA.
 
Chief Thracian said:
alt.comp.hardware, alt.comp.periphs

As of two weeks ago, I can no longer Internet-connect
the usual way, via my Supra Express 56k modem. (My OS
is Windoze98.) Here's the problem:

I need to unplug and replug the telephone line going to
the modem, to restore the dial tone. If not, the phone
line remains open, so I can't receive or send phone
calls. It's as if the modem lost its ability to hang
up. (Problem remains even when my computer is shut
down...so I know it's not OS--or even
computer--related.)
Click to expand...

How many phones do you have plugged in in the whole house? They all
add up and eventually cause problems.

Try unplugging a couple phones and see if the problem goes awa.
Now, when I don't need to get on the 'net, I unplug the
phone line from the modem, and plug it into the back of
my answering machine... which then allows me to receive
and make regular phone calls.

Is this a burnt-out modem chip? Or can I possibly
restore my modem to its former excellent condition?
Where do I start? I have yet to find the appropriate
help file. If you know of one, please direct me to it.
Otherwise, I'd much appreciate someone guiding me
through possible maneuvers to correct the error.
Click to expand...

If it's broken, it's most likely a stuck relay. If it's just a normal
relay, it should be easy to replace.
 
Yours is a classic problem created by transient from AC
mains. Common mode transient sought earth ground. Incoming
on AC wire that makes direct connection (through motherboard)
to modem. Outgoing to earth ground via phone line. Since the
surge was so minimal, a PNP transistor that drives off hook
relay is permanently shorted. To get phone line free, remove
phone line from modem OR remove power to computer. Second
condition must be true if this is PNP transistor problem.
Modem can be repaired by soldering a new PNP transistor
between modem controller IC and that off-hook relay circuit.

Your failure suggests no 'whole house' surge protector was
installed on the most common source of lightning damage - AC
electric. Lightning found earth ground via your modem
regardless of whether you had computer powered. Even worse, a
plug-in and adjacent surge protector makes this type of damage
more probable.
 
Your failure suggests no 'whole house' surge protector was
installed on the most common source of lightning damage - AC
electric. Lightning found earth ground via your modem
regardless of whether you had computer powered. Even worse, a
plug-in and adjacent surge protector makes this type of damage
more probable.
Click to expand...

Even worse, a whole house protector on the AC would not have made a
bit of difference if the lightning came in through the phone line. It
still would have found ground through the PC just the same.
 
Phone lines typically have a 'whole house' protector
installed free by the telco. If a destructive surge was
incoming on that phone line, then 1) lightning would have to
bypass a higher and more exposed electric lines to get to
phone line, 2) 'whole house' protector for phone line was not
installed or homeowner compromised the protectors all so
critical ground wire, or 3) home did not provide / use a
single point ground. So many reasons why phone lines are
rarely source of surges and why AC electric is source of most
surge damage. AC electric is the one utility that typically
has no protection - especially if using plug-in surge
protectors.

Fax, portable phone base station, and modem damage usually
is from a surge incoming on AC electric. Of course. Most
every home is still wired as if the transistor did not exist;
no 'whole house' protector on the most common source of
destructive surges - AC electric. Even worse, many older
homes have disconnected earth grounds. No earth ground means
no effective protection - no matter how many ineffective
plug-in protectors are installed.
 
w_tom said:
Phone lines typically have a 'whole house' protector
installed free by the telco.
Click to expand...

Thanks for your helpful input...likewise, to everyone else who chimed
in.
I kinda thought this was NOT a problem that could be
software-corrected
(such as add ATH to the modem redial command string). I've gotten a
lot
of years out of this fine modem; and consider myself lucky that my
system
has suffered no other surge/spike damage in any other component.

I live in an OLD building (built 1904) with old circuitry. Spikes are
frequent, due to the elevator (the original!)...and I do use a
Backup-UPS
battery that allows me up to five minutes to shut down.

In reply to Phrederik, who asked how many phones I use: just one...so
the problem is simple to isolate. I believe I have experienced a short
in the modem: a common experience as others here have explained. But
not from lightening, which is rare in my neck of the woods (San
Francisco).

Thanks again, everyone!
 
An old story from early days of computers. New computer
would not work. Tech ran diagnostics all night. Computer
never failed until he left to get coffee. It got so bad that
he would loudly announce his thirst and stomp out of the
room. Then sneak back and peek around the corner. Still
computer would not crash - until he actually came back with
coffee.

Eventually problem was traced to how one elevator was
grounded. Everytime he took that elevator for coffee, it
crashed the computer. Wonder why some people believe in
ghosts? Who would have guessed how important grounding must
be understood?
 
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