modem holds line..
 

even when out of the PC-what could be the cause?

modem holds line..
 

On 17 Oct 2005 12:56:12 -0700, put finger to
keyboard and composed:

even when out of the PC-what could be the cause?

IME the most common cause is stuck contacts in the hook relay. Does
the dialtone return if you disconnect and reconnect the modem to the
phone line?

-- Franc Zabkar

Please remove one 'i' from my address when replying by email.

modem holds line..
 

wrote:
even when out of the PC-what could be the cause?


Hi...

You'll see a little (probably black) box very near to where
the telephone jacks are. Give itaa gentle tap or two with the
handle of a pocket screwdriver.

If this causes it to release the line, then the relay is
sticking. It may from then on continue to operate, or it
may stick again next time you use it.

Ken

modem holds line..
 

the relay (soldered) has approx 20kohms between the coil and 200k
between the output, when dis/reconnecting the dialtone returns but then
again goes busy by itself!

modem holds line..
 

On 18 Oct 2005 04:27:28 -0700, put finger to
keyboard and composed:

the relay (soldered) has approx 20kohms between the coil and 200k
between the output, when dis/reconnecting the dialtone returns but then
again goes busy by itself!

That's the same behaviour you get when you take your phone offhook and
allow the dialtone to time out. It means that something is placing a
load across the line, but not a dead short. If the relay contacts are
open, then the only other culprit that comes to mind is a MOV, but IME
these usually fail OC. I'd measure the voltage between the tip and
ring inputs. In my case it is 53V when on-hook and about 10V when
off-hook. Disconnect various components until the voltage is back to
normal.

-- Franc Zabkar

Please remove one 'i' from my address when replying by email.

modem holds line..
 

In message
Franc Zabkar wrote:

the relay (soldered) has approx 20kohms between the coil and 200k
between the output, when dis/reconnecting the dialtone returns but then
again goes busy by itself!

That's the same behaviour you get when you take your phone offhook and
allow the dialtone to time out. It means that something is placing a
load across the line, but not a dead short. If the relay contacts are
open, then the only other culprit that comes to mind is a MOV, but IME
these usually fail OC. I'd measure the voltage between the tip and
ring inputs. In my case it is 53V when on-hook and about 10V when
off-hook. Disconnect various components until the voltage is back to
normal.

Many phones, and some modems, have a diode bridge across the line to
power part of the electronics (in a non-DECT phone, all of it).

These tend to go leaky when a surge, e.g. lightning somewhere near,
causes damage short of total destruction ...

--
Peter Duck

modem holds line..
 

wrote:

even when out of the PC-what could be the cause?

lighting protection is still working and never
took a break ?


--
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5

modem holds line..
 

On 2005-10-18, wrote:
the relay (soldered) has approx 20kohms between the coil and 200k
between the output, when dis/reconnecting the dialtone returns but then
again goes busy by itself!

That first figure sounds way too high, 200 ohms would be the low side of
believable can you check again?

seing as it doesn't look like a short

also can you measure the current through the modem when it's connected to the
phone line (but on hook/powered off) a ohm meter running at 1.5-9V soetimes
sees things differently to the phone line (48V on-hook)

Is it possible you've measured the ring detector and not the relay?

Bye.
Jasen

modem holds line..
 

On Wed, 19 Oct 2005 00:31:37 +0100, Peter Duck
put finger to keyboard and composed:

In message
Franc Zabkar wrote:

the relay (soldered) has approx 20kohms between the coil and 200k
between the output, when dis/reconnecting the dialtone returns but then
again goes busy by itself!

That's the same behaviour you get when you take your phone offhook and
allow the dialtone to time out. It means that something is placing a
load across the line, but not a dead short. If the relay contacts are
open, then the only other culprit that comes to mind is a MOV, but IME
these usually fail OC. I'd measure the voltage between the tip and
ring inputs. In my case it is 53V when on-hook and about 10V when
off-hook. Disconnect various components until the voltage is back to
normal.

Many phones, and some modems, have a diode bridge across the line to
power part of the electronics (in a non-DECT phone, all of it).

These tend to go leaky when a surge, e.g. lightning somewhere near,
causes damage short of total destruction ...

AFAICS the diode bridge (in a transformer based modem) would always be
on the host side of the relay contacts, not the line side. The only
circuitry on the line side would be the ringer, and this would be
isolated by a 1uF 250V DC blocking cap.

-- Franc Zabkar

Please remove one 'i' from my address when replying by email.

modem holds line..
 

Jasen Betts wrote:
On 2005-10-18, wrote:
the relay (soldered) has approx 20kohms between the coil and 200k
between the output, when dis/reconnecting the dialtone returns but then
again goes busy by itself!

That first figure sounds way too high, 200 ohms would be the low side of
believable can you check again?

seing as it doesn't look like a short

also can you measure the current through the modem when it's connected to the
phone line (but on hook/powered off) a ohm meter running at 1.5-9V soetimes
sees things differently to the phone line (48V on-hook)

Is it possible you've measured the ring detector and not the relay?

Bye.
Jasen

took the modem out of the pc, relay in:0.5kohms both ways (the flyback
diode seems to be out but not sure if it can be tested without
desoldering) and out:approx 500k ;
when I plug in the line the modem goes offhook but not right away and
the relay
output closes.There is a diode bridge but cannot really tell if the
relay is on the host side though it is rated 0.5A 20V/0.1A 100V; MOV
is open at all times, How do I test OC and can I pull it out if I do
not expect any calls?

modem holds line..
 

["Followup-To:" header set to sci.electronics.basics.]
On 2005-10-19, wrote:

Jasen Betts wrote:
On 2005-10-18, wrote:
the relay (soldered) has approx 20kohms between the coil and 200k
between the output, when dis/reconnecting the dialtone returns but then
again goes busy by itself!

That first figure sounds way too high, 200 ohms would be the low side of
believable can you check again?

seing as it doesn't look like a short

also can you measure the current through the modem when it's connected to the
phone line (but on hook/powered off) a ohm meter running at 1.5-9V soetimes
sees things differently to the phone line (48V on-hook)

Is it possible you've measured the ring detector and not the relay?


took the modem out of the pc, relay in:0.5kohms both ways (the flyback
diode seems to be out but not sure if it can be tested without
desoldering) and out:approx 500k ;

That sounds much better.

when I plug in the line the modem goes offhook but not right away and
the relay output closes.

ooh... you hear the relay closing? that doesn't sound like a relay fault.

sounds line a fault elsewhere

caa you use a terminal program to "talk to" the modem
if so run all the tests.
at&t1
at&t2

etc...

see how it responds to commands like

ath (go on hook)
ath1 (go off hook)
atxdp9 (dial nine pulses)

both with the modem connected to to the phone line and disconnected.

There is a diode bridge but cannot really tell if the
relay is on the host side though it is rated 0.5A 20V/0.1A 100V;

could the bridge be for the modems power supply?

at 20V rating it'll be atleast half switched by the modem.
otherwise behing it

MOV is open at all times,
How do I test OC and can I pull it out if I do
not expect any calls?

huh?

Bye.
Jasen

modem holds line..
 

On 19 Oct 2005 09:25:23 -0700, put finger to
keyboard and composed:


Jasen Betts wrote:
On 2005-10-18, wrote:
the relay (soldered) has approx 20kohms between the coil and 200k
between the output, when dis/reconnecting the dialtone returns but then
again goes busy by itself!

That first figure sounds way too high, 200 ohms would be the low side of
believable can you check again?

seing as it doesn't look like a short

also can you measure the current through the modem when it's connected to the
phone line (but on hook/powered off) a ohm meter running at 1.5-9V soetimes
sees things differently to the phone line (48V on-hook)

Is it possible you've measured the ring detector and not the relay?

Bye.
Jasen

took the modem out of the pc, relay in:0.5kohms both ways (the flyback
diode seems to be out but not sure if it can be tested without
desoldering) and out:approx 500k ;
when I plug in the line the modem goes offhook but not right away and
the relay
output closes.There is a diode bridge but cannot really tell if the
relay is on the host side though it is rated 0.5A 20V/0.1A 100V; MOV
is open at all times, How do I test OC and can I pull it out if I do
not expect any calls?

So it's an internal modem, and you've taken it out of the PC? If so,
then this means that the hook relay's coil would not be getting any
power. If the relay contacts are closing under these conditions, then
this means that the relay itself is faulty. To confirm this, desolder
one of the contacts and monitor the tip and ring voltage.

-- Franc Zabkar

Please remove one 'i' from my address when replying by email.

modem holds line..
 

Ambient Ham chipset Modem ATI diagnostics OK.Disabled 'wait for dial
tone' and It dials but it cannot connect and after that it just
'arrests' the line; tried at&t1 in Hyper terminal-modem 'connects' at
115200 and spits some characters, ath/h1 ok; checked line-around 50
volts but when modem plugged in, it goes to 13v, desoldered MOV is ok
but low resistance measured at it's modem board contacts;bridge output
goes to darlington...?; as mentioned-in or out of the PC when I plug in
the line first you can hear the dial tone &then after 1-2 min. modem is
holding the line

modem holds line..
 

On 21 Oct 2005 12:55:26 -0700, put finger to
keyboard and composed:

Ambient Ham chipset Modem ATI diagnostics OK.Disabled 'wait for dial
tone' and It dials but it cannot connect and after that it just
'arrests' the line; tried at&t1 in Hyper terminal-modem 'connects' at
115200 and spits some characters,

The AT&Tn commands test the data path to the DSP. They are not really
helpful when troubleshooting a DAA fault such as yours.

ath/h1 ok; checked line-around 50
volts but when modem plugged in, it goes to 13v,

If you are measuring 13V on both sides of the relay contacts, then the
relay is stuck.

desoldered MOV is ok
but low resistance measured at it's modem board contacts;bridge output
goes to darlington...?;

Yes, that's the loop current stabilisation circuit, or whatever it is
called. It would be on the host side of the relay contacts. If you are
measuring any voltage there, then the relay is stuck.

as mentioned-in or out of the PC when I plug in
the line first you can hear the dial tone &then after 1-2 min. modem is
holding the line

Change the relay, or at least desolder it.

-- Franc Zabkar

Please remove one 'i' from my address when replying by email.

modem holds line..
 

Franc Zabkar је напиÑ?ао
On 21 Oct 2005 12:55:26 -0700, put finger to
keyboard and composed:

Ambient Ham chipset Modem ATI diagnostics OK.Disabled 'wait for dial
tone' and It dials but it cannot connect and after that it just
'arrests' the line; tried at&t1 in Hyper terminal-modem 'connects' at
115200 and spits some characters,

The AT&Tn commands test the data path to the DSP. They are not really
helpful when troubleshooting a DAA fault such as yours.

ath/h1 ok; checked line-around 50
volts but when modem plugged in, it goes to 13v,

If you are measuring 13V on both sides of the relay contacts, then the
relay is stuck.

desoldered MOV is ok
but low resistance measured at it's modem board contacts;bridge output
goes to darlington...?;

Yes, that's the loop current stabilisation circuit, or whatever it is
called. It would be on the host side of the relay contacts. If you are
measuring any voltage there, then the relay is stuck.

as mentioned-in or out of the PC when I plug in
the line first you can hear the dial tone &then after 1-2 min. modem is
holding the line

Change the relay, or at least desolder it.

-- Franc Zabkar

Please remove one 'i' from my address when replying by email.

Shouldn't I suspect the transistor i.e. the circuit feeding the
coil-looks like upon line plug-in voltage buids up gradually to switch
the relay. You mentioned OC-if it's only function is ring detection can
i remove it, though OC's input diode seems to be connected also to
relay coil...

modem holds line..
 

If you add: &C2&D2

to your modem init string, it should hang up.


On 21 Oct 2005 12:55:26 -0700, wrote:





Ambient Ham chipset Modem ATI diagnostics OK.Disabled 'wait for dial
tone' and It dials but it cannot connect and after that it just
'arrests' the line; tried at&t1 in Hyper terminal-modem 'connects' at
115200 and spits some characters, ath/h1 ok; checked line-around 50
volts but when modem plugged in, it goes to 13v, desoldered MOV is ok
but low resistance measured at it's modem board contacts;bridge output
goes to darlington...?; as mentioned-in or out of the PC when I plug in
the line first you can hear the dial tone &then after 1-2 min. modem is
holding the line

modem holds line..
 

On 22 Oct 2005 04:54:15 -0700, put finger to
keyboard and composed:


Franc Zabkar ?? ???????
On 21 Oct 2005 12:55:26 -0700, put finger to
keyboard and composed:

Ambient Ham chipset Modem ATI diagnostics OK.Disabled 'wait for dial
tone' and It dials but it cannot connect and after that it just
'arrests' the line; tried at&t1 in Hyper terminal-modem 'connects' at
115200 and spits some characters,

The AT&Tn commands test the data path to the DSP. They are not really
helpful when troubleshooting a DAA fault such as yours.

ath/h1 ok; checked line-around 50
volts but when modem plugged in, it goes to 13v,

If you are measuring 13V on both sides of the relay contacts, then the
relay is stuck.

desoldered MOV is ok
but low resistance measured at it's modem board contacts;bridge output
goes to darlington...?;

Yes, that's the loop current stabilisation circuit, or whatever it is
called. It would be on the host side of the relay contacts. If you are
measuring any voltage there, then the relay is stuck.

as mentioned-in or out of the PC when I plug in
the line first you can hear the dial tone &then after 1-2 min. modem is
holding the line

Change the relay, or at least desolder it.

-- Franc Zabkar

Please remove one 'i' from my address when replying by email.

Shouldn't I suspect the transistor i.e. the circuit feeding the
coil-looks like upon line plug-in voltage buids up gradually to switch
the relay.

The transistor is driven from the DSP chip which gets its power from
the slot. The relay's coil voltage also comes from the slot. No slot =
no power. If the transistor or coil are getting power from the phone
line, then you have a *serious* isolation problem.

Change the relay, or at least desolder it.

You mentioned OC-if it's only function is ring detection can
i remove it, though OC's input diode seems to be connected also to
relay coil...

OC = open circuit

-- Franc Zabkar

Please remove one 'i' from my address when replying by email.

modem holds line..
 

Franc Zabkar wrote:
On 22 Oct 2005 04:54:15 -0700, put finger to
keyboard and composed:


Franc Zabkar ?? ???????
On 21 Oct 2005 12:55:26 -0700, put finger to
keyboard and composed:

Ambient Ham chipset Modem ATI diagnostics OK.Disabled 'wait for dial
tone' and It dials but it cannot connect and after that it just
'arrests' the line; tried at&t1 in Hyper terminal-modem 'connects' at
115200 and spits some characters,

The AT&Tn commands test the data path to the DSP. They are not really
helpful when troubleshooting a DAA fault such as yours.

ath/h1 ok; checked line-around 50
volts but when modem plugged in, it goes to 13v,

If you are measuring 13V on both sides of the relay contacts, then the
relay is stuck.

desoldered MOV is ok
but low resistance measured at it's modem board contacts;bridge output
goes to darlington...?;

Yes, that's the loop current stabilisation circuit, or whatever it is
called. It would be on the host side of the relay contacts. If you are
measuring any voltage there, then the relay is stuck.

as mentioned-in or out of the PC when I plug in
the line first you can hear the dial tone &then after 1-2 min. modem is
holding the line

Change the relay, or at least desolder it.

-- Franc Zabkar

Please remove one 'i' from my address when replying by email.

Shouldn't I suspect the transistor i.e. the circuit feeding the
coil-looks like upon line plug-in voltage buids up gradually to switch
the relay.

The transistor is driven from the DSP chip which gets its power from
the slot. The relay's coil voltage also comes from the slot. No slot =
no power. If the transistor or coil are getting power from the phone
line, then you have a *serious* isolation problem.

Change the relay, or at least desolder it.

You mentioned OC-if it's only function is ring detection can
i remove it, though OC's input diode seems to be connected also to
relay coil...

OC = open circuit

-- Franc Zabkar

Please remove one 'i' from my address when replying by email.

Thanks again
checked the transistor driving the coil-ok as well as flyback diode
Seems defective optocoupler(OC) could be connecting line to the relay
even when modem out of PC?

modem holds line..
 

Franc Zabkar wrote:
On 22 Oct 2005 04:54:15 -0700, put finger to
keyboard and composed:


Franc Zabkar ?? ???????
On 21 Oct 2005 12:55:26 -0700, put finger to
keyboard and composed:

Ambient Ham chipset Modem ATI diagnostics OK.Disabled 'wait for dial
tone' and It dials but it cannot connect and after that it just
'arrests' the line; tried at&t1 in Hyper terminal-modem 'connects' at
115200 and spits some characters,

The AT&Tn commands test the data path to the DSP. They are not really
helpful when troubleshooting a DAA fault such as yours.

ath/h1 ok; checked line-around 50
volts but when modem plugged in, it goes to 13v,

If you are measuring 13V on both sides of the relay contacts, then the
relay is stuck.

desoldered MOV is ok
but low resistance measured at it's modem board contacts;bridge output
goes to darlington...?;

Yes, that's the loop current stabilisation circuit, or whatever it is
called. It would be on the host side of the relay contacts. If you are
measuring any voltage there, then the relay is stuck.

as mentioned-in or out of the PC when I plug in
the line first you can hear the dial tone &then after 1-2 min. modem is
holding the line

Change the relay, or at least desolder it.

-- Franc Zabkar

Please remove one 'i' from my address when replying by email.

Shouldn't I suspect the transistor i.e. the circuit feeding the
coil-looks like upon line plug-in voltage buids up gradually to switch
the relay.

The transistor is driven from the DSP chip which gets its power from
the slot. The relay's coil voltage also comes from the slot. No slot =
no power. If the transistor or coil are getting power from the phone
line, then you have a *serious* isolation problem.

Change the relay, or at least desolder it.

You mentioned OC-if it's only function is ring detection can
i remove it, though OC's input diode seems to be connected also to
relay coil...

OC = open circuit

-- Franc Zabkar

Please remove one 'i' from my address when replying by email.

checked relay-desoldered clicks just fine but is it possible that when
defective it closes
the output without stimulus at the coil?
here is daa schematic
http://www.geocities.com/anglomont/daa.jpg
Since mov is ok I do not see what else can arrest the line...

modem holds line..
 

wrote:
Franc Zabkar wrote:

On 22 Oct 2005 04:54:15 -0700, put finger to
keyboard and composed:


Franc Zabkar ?? ???????

On 21 Oct 2005 12:55:26 -0700, put finger to
keyboard and composed:


Ambient Ham chipset Modem ATI diagnostics OK.Disabled 'wait for dial
tone' and It dials but it cannot connect and after that it just
'arrests' the line; tried at&t1 in Hyper terminal-modem 'connects' at
115200 and spits some characters,

The AT&Tn commands test the data path to the DSP. They are not really
helpful when troubleshooting a DAA fault such as yours.


ath/h1 ok; checked line-around 50
volts but when modem plugged in, it goes to 13v,

If you are measuring 13V on both sides of the relay contacts, then the
relay is stuck.


desoldered MOV is ok
but low resistance measured at it's modem board contacts;bridge output
goes to darlington...?;

Yes, that's the loop current stabilisation circuit, or whatever it is
called. It would be on the host side of the relay contacts. If you are
measuring any voltage there, then the relay is stuck.


as mentioned-in or out of the PC when I plug in
the line first you can hear the dial tone &then after 1-2 min. modem is
holding the line

Change the relay, or at least desolder it.

-- Franc Zabkar

Please remove one 'i' from my address when replying by email.

Shouldn't I suspect the transistor i.e. the circuit feeding the
coil-looks like upon line plug-in voltage buids up gradually to switch
the relay.

The transistor is driven from the DSP chip which gets its power from
the slot. The relay's coil voltage also comes from the slot. No slot =
no power. If the transistor or coil are getting power from the phone
line, then you have a *serious* isolation problem.

Change the relay, or at least desolder it.


You mentioned OC-if it's only function is ring detection can
i remove it, though OC's input diode seems to be connected also to
relay coil...

OC = open circuit

-- Franc Zabkar

Please remove one 'i' from my address when replying by email.


checked relay-desoldered clicks just fine but is it possible that when
defective it closes
the output without stimulus at the coil?
here is daa schematic
http://www.geocities.com/anglomont/daa.jpg
Since mov is ok I do not see what else can arrest the line...

Hi...

That relay is so small and flimsy it may well be that you can hear
it click even though the contacts may be welded shut.

Ken

modem holds line..
 

I suspect a problem with your schematic. For example, the
NPR transistor that drives the off hook relay would be a poor
design. Most use a PNP transistor that connects to +5V - not
to ground. That would also ground the opto coupler circuit
since the optocoupler should not affect off-hook relay.

The typical destructive transient comes from AC mains
seeking earth ground via the telephone line surge protection.
A most common path to earth is through that PNP transistor,
from relay coil to relay wiper, then on into phone line.

If the transient is small, PNP transistor becomes shorted
causing dial tone to time out when computer power is on. If
the transient is larger, PNP transistors becomes open
circuited resulting in the 'No Dialtone Detected' error
message.

Why a PNP transistor? Higher breakdown voltage between
collector and base provides protection for the modem's
computer. Your schematic provides no such protection - base
to emitter.

If I read everything correctly (and I have not been careful
with the details), it is a classic 'PNP failed shorted'
condition. A 'no dialtone' until computer power is removed so
that relay can open.

wrote:
checked relay-desoldered clicks just fine but is it possible that when
defective it closes
the output without stimulus at the coil?
here is daa schematic
http://www.geocities.com/anglomont/daa.jpg
Since mov is ok I do not see what else can arrest the line...