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modem line takeover?!
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Pooh Bear
electronics forum Guru


Joined: 24 Mar 2005
Posts: 3507

PostPosted: Mon Jun 19, 2006 6:10 pm    Post subject: Re: modem line takeover?! Reply with quote

j_slobo@hotmail.com wrote:

Quote:
Looked at several Motorola SM56 modems an all have the same fault-non
infinite resistance at line jack which causes them to take over the
line once the line is plugged, so none of the telephones can be used!

Ah ! Is that what it is ? I installed one of those too and wondered what the
trouble is. If you're quick I could get it to dial out but it never dropped the
line after connecting.

Quote:
Checked the MOV and it is ok and there is no relay on modem !(at least
not a box type, just few too many smd transistors doing smth?)
There is a diode bridge so the line interface is a 'dry transformer'
type.Once you disconnect the line and plug it back in, it goes free for
few moments...
What do you suggest I check, other than the optocoupler?( because I
think it has to be ok since the modem is actually working if I manage
to hook to provider in few seconds before it takes over the line)

Who did you buy yours from ? Why are they selling something that doesn't work ?

Have you got as far as drawing a circuit ? I hadn't gone any further with mine
since it's not very urgent.

Graham
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j_slobo@hotmail.com
electronics forum beginner


Joined: 06 Oct 2005
Posts: 10

PostPosted: Mon Jun 19, 2006 6:50 pm    Post subject: Re: modem line takeover?! Reply with quote

Pooh Bear wrote:
Quote:
j_slobo@hotmail.com wrote:

Looked at several Motorola SM56 modems an all have the same fault-non
infinite resistance at line jack which causes them to take over the
line once the line is plugged, so none of the telephones can be used!

Ah ! Is that what it is ? I installed one of those too and wondered what the
trouble is. If you're quick I could get it to dial out but it never dropped the
line after connecting.

Checked the MOV and it is ok and there is no relay on modem !(at least
not a box type, just few too many smd transistors doing smth?)
There is a diode bridge so the line interface is a 'dry transformer'
type.Once you disconnect the line and plug it back in, it goes free for
few moments...
What do you suggest I check, other than the optocoupler?( because I
think it has to be ok since the modem is actually working if I manage
to hook to provider in few seconds before it takes over the line)

Who did you buy yours from ? Why are they selling something that doesn't work ?

Have you got as far as drawing a circuit ? I hadn't gone any further with mine
since it's not very urgent.

Graham

Nope and I doubt I will be able -it's just too tiny!
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default
electronics forum Guru Wannabe


Joined: 03 May 2005
Posts: 175

PostPosted: Mon Jun 19, 2006 8:37 pm    Post subject: Re: modem line takeover?! Reply with quote

On 19 Jun 2006 08:44:34 -0700, j_slobo@hotmail.com wrote:

Quote:
Looked at several Motorola SM56 modems an all have the same fault-non
infinite resistance at line jack which causes them to take over the
line once the line is plugged, so none of the telephones can be used!
Checked the MOV and it is ok and there is no relay on modem !(at least
not a box type, just few too many smd transistors doing smth?)
There is a diode bridge so the line interface is a 'dry transformer'
type.Once you disconnect the line and plug it back in, it goes free for
few moments...
What do you suggest I check, other than the optocoupler?( because I
think it has to be ok since the modem is actually working if I manage
to hook to provider in few seconds before it takes over the line)

That sounds weird/unbelievable. Check on-line to see if there's a
firmware update or perhaps an AT command that will change its
behavior?

I'm assuming it is new and just behaves this way and didn't go bad . .
.. The fact that you see that delay seems to suggest it may be working
but just a command/software problem - also if there's a pass-through
jack for the telephone make sure the line goes into the correct jack.

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Franc Zabkar
electronics forum Guru


Joined: 01 May 2005
Posts: 616

PostPosted: Mon Jun 19, 2006 9:17 pm    Post subject: Re: modem line takeover?! Reply with quote

On 19 Jun 2006 08:44:34 -0700, j_slobo@hotmail.com put finger to
keyboard and composed:

Quote:
Looked at several Motorola SM56 modems an all have the same fault-non
infinite resistance at line jack which causes them to take over the
line once the line is plugged, so none of the telephones can be used!
Checked the MOV and it is ok and there is no relay on modem !(at least
not a box type, just few too many smd transistors doing smth?)

There is a diode bridge so the line interface is a 'dry transformer'
type.

If there is a transformer, then the DAA is probably dry, as you say.
Otherwise there would usually be two chips, one on the line side and
one on the host side, with two or three ceramic caps providing the
isolation.

Quote:
Once you disconnect the line and plug it back in, it goes free for
few moments...

The symptom you are describing is that of stuck contacts in the hook
relay. But then you say that there is none ...

Quote:
What do you suggest I check, other than the optocoupler?

The optocoupler is there to detect the ring voltage and to isolate it
from the host side electronics. There should be a 1uF 250V cap in
series with its input, as well as a ~10K resistor.

Quote:
( because I
think it has to be ok since the modem is actually working if I manage
to hook to provider in few seconds before it takes over the line)

There has to be some way for the host side electronics to control the
off-hook/on-hook state of the DAA. Look for a hook relay, possibly
solid state. Otherwise look for any device that bridges the gap
between the host and line sides.

Can you upload a photo to your web space?

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.
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Franc Zabkar
electronics forum Guru


Joined: 01 May 2005
Posts: 616

PostPosted: Mon Jun 19, 2006 9:21 pm    Post subject: Re: modem line takeover?! Reply with quote

On 19 Jun 2006 08:44:34 -0700, j_slobo@hotmail.com put finger to
keyboard and composed:

Quote:
Looked at several Motorola SM56 modems an all have the same fault-non
infinite resistance at line jack which causes them to take over the
line once the line is plugged, so none of the telephones can be used!
Checked the MOV and it is ok and there is no relay on modem !(at least
not a box type, just few too many smd transistors doing smth?)
There is a diode bridge so the line interface is a 'dry transformer'
type.Once you disconnect the line and plug it back in, it goes free for
few moments...
What do you suggest I check, other than the optocoupler?( because I
think it has to be ok since the modem is actually working if I manage
to hook to provider in few seconds before it takes over the line)

One thing to check is whether the modem grabs the line when the PC is
powered down. If not, then this would point to a problem on the host
side.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.
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Pooh Bear
electronics forum Guru


Joined: 24 Mar 2005
Posts: 3507

PostPosted: Mon Jun 19, 2006 11:48 pm    Post subject: Re: modem line takeover?! Reply with quote

Franc Zabkar wrote:

Quote:
On 19 Jun 2006 08:44:34 -0700, j_slobo@hotmail.com put finger to
keyboard and composed:

Looked at several Motorola SM56 modems an all have the same fault-non
infinite resistance at line jack which causes them to take over the
line once the line is plugged, so none of the telephones can be used!
Checked the MOV and it is ok and there is no relay on modem !(at least
not a box type, just few too many smd transistors doing smth?)

There is a diode bridge so the line interface is a 'dry transformer'
type.

If there is a transformer, then the DAA is probably dry, as you say.
Otherwise there would usually be two chips, one on the line side and
one on the host side, with two or three ceramic caps providing the
isolation.

The one I have has no relay or transformer.

I'm seeing 19M across the line on the bare pcb.

I'll look further.

It has some approvals logos printed on it but I guess they could be fraudulent.

Graham
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hhc314@yahoo.com
electronics forum addict


Joined: 11 Sep 2005
Posts: 88

PostPosted: Tue Jun 20, 2006 4:34 am    Post subject: Re: modem line takeover?! Reply with quote

My guess is that you're running into the same problem that I originally
had with my USR 56K Fax modem, until I learned how to set its switches.
The problem that I ran into with the SM56 is that the Motorola website
evidently lacks the documentation telling you where to set the switches
for the configuration that you need, plus how to set them. All that I
could find on the SM56 at the Motorola website was a few pages of PR
and advertising, without any technical detail.

I seriously doubt that the SM56 hardware is at fault, but their
published documentation is certainly wanting of more detailed technical
instructions.

I'd suggest that you email Motorola about this problem.

Harry C.


j_slobo@hotmail.com wrote:
Quote:
Looked at several Motorola SM56 modems an all have the same fault-non
infinite resistance at line jack which causes them to take over the
line once the line is plugged, so none of the telephones can be used!
Checked the MOV and it is ok and there is no relay on modem !(at least
not a box type, just few too many smd transistors doing smth?)
There is a diode bridge so the line interface is a 'dry transformer'
type.Once you disconnect the line and plug it back in, it goes free for
few moments...
What do you suggest I check, other than the optocoupler?( because I
think it has to be ok since the modem is actually working if I manage
to hook to provider in few seconds before it takes over the line)
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Stan
electronics forum beginner


Joined: 01 May 2005
Posts: 31

PostPosted: Tue Jun 20, 2006 5:02 am    Post subject: Re: modem line takeover?! Reply with quote

j_slobo@hotmail.com wrote:

}Looked at several Motorola SM56 modems an all have the same fault-non
}infinite resistance at line jack...

Non-infinite resistance when un-installed (i.e. not in the PC)? Or does it
go non-infinite only when installed & pc powered on?

Stan.
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jasen
electronics forum Guru Wannabe


Joined: 18 Jun 2006
Posts: 204

PostPosted: Tue Jun 20, 2006 8:48 am    Post subject: Re: modem line takeover?! Reply with quote

On 2006-06-19, Pooh Bear <rabbitsfriendsandrelations@hotmail.com> wrote:
Quote:


Franc Zabkar wrote:

On 19 Jun 2006 08:44:34 -0700, j_slobo@hotmail.com put finger to
keyboard and composed:

Looked at several Motorola SM56 modems an all have the same fault-non
infinite resistance at line jack which causes them to take over the
line once the line is plugged, so none of the telephones can be used!
Checked the MOV and it is ok and there is no relay on modem !(at least
not a box type, just few too many smd transistors doing smth?)

There is a diode bridge so the line interface is a 'dry transformer'
type.

If there is a transformer, then the DAA is probably dry, as you say.
Otherwise there would usually be two chips, one on the line side and
one on the host side, with two or three ceramic caps providing the
isolation.

The one I have has no relay or transformer.

I'm seeing 19M across the line on the bare pcb.

At 48V ?

Bye.
Jasen
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Franc Zabkar
electronics forum Guru


Joined: 01 May 2005
Posts: 616

PostPosted: Tue Jun 20, 2006 9:33 am    Post subject: Re: modem line takeover?! Reply with quote

On 19 Jun 2006 21:34:10 -0700, hhc314@yahoo.com put finger to keyboard
and composed:

Quote:
My guess is that you're running into the same problem that I originally
had with my USR 56K Fax modem, until I learned how to set its switches.
The problem that I ran into with the SM56 is that the Motorola website
evidently lacks the documentation telling you where to set the switches

That's because there are none. The SM56 is an internal (S)oft(M)odem.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.
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Franc Zabkar
electronics forum Guru


Joined: 01 May 2005
Posts: 616

PostPosted: Tue Jun 20, 2006 9:33 am    Post subject: Re: modem line takeover?! Reply with quote

On Tue, 20 Jun 2006 00:48:22 +0100, Pooh Bear
<rabbitsfriendsandrelations@hotmail.com> put finger to keyboard and
composed:

Quote:


Franc Zabkar wrote:

On 19 Jun 2006 08:44:34 -0700, j_slobo@hotmail.com put finger to
keyboard and composed:

Looked at several Motorola SM56 modems an all have the same fault-non
infinite resistance at line jack which causes them to take over the
line once the line is plugged, so none of the telephones can be used!
Checked the MOV and it is ok and there is no relay on modem !(at least
not a box type, just few too many smd transistors doing smth?)

There is a diode bridge so the line interface is a 'dry transformer'
type.

If there is a transformer, then the DAA is probably dry, as you say.
Otherwise there would usually be two chips, one on the line side and
one on the host side, with two or three ceramic caps providing the
isolation.

The one I have has no relay or transformer.

I'm seeing 19M across the line on the bare pcb.

You might be looking into a diode bridge, either discrete or internal
to a line side chip.

I'd be checking whether the modem goes off-hook when the PC is powered
down. If not, then your line side electronics is probably OK. Next I
would check whether the modem grabs the line during the POST, ie
before its drivers have a chance to load.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.
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Franc Zabkar
electronics forum Guru


Joined: 01 May 2005
Posts: 616

PostPosted: Tue Jun 20, 2006 2:53 pm    Post subject: Re: modem line takeover?! Reply with quote

On 20 Jun 2006 17:26:02 -0700, hhc314@yahoo.com put finger to keyboard
and composed:

Quote:
Franc, the USR 56K Faxmodem is also an internal soft modem (new
word?).

Modems are classified as "soft", controllerless, or "hard". The former
has a DAA and not much else, the second has a DAA + DSP, and the
latter has a DAA + DSP + controller. If any functional block is
missing, then it is emulated by a driver. Softmodems are technically
the worst because they rely on the host CPU to do everything. That is
not to say that softmodems are necessarily bad.

Quote:
All of today's modems have setup switch settings, either hard or soft.

Some external USR modems, eg Courier, had a physical bank of switches.
I thought you were referring to them.

Quote:
Without these the modem would be relatively inflexible and useless.
It's usually the modem initialization control command that sets them
up, and they typically run from S1 to S7 or more. These determine such
basic things such as if the modem is on-line continuously, normally
off-line, auto-answer, automatic retries, etc. You need to have a copy
of the chipset producer's technical data sheet to learn how to use
them, without which the chipset is virtually useless.

I know of no S-register that would cause a modem to power up in an
off-hook state, nor any reason why you would want it to. If the
software or the modem's driver is commanding it to go off-hook, then
something is very wrong. Having said that, I seem to recall some
Conexant modems that would not release the line after disconnection.
The fix was a driver update.

If you are a Windows user, your modemlog file will tell you which
commands are being sent to your modem, and how the modem is
responding.

Quote:
Without knowledge of what these settings mean and how to use them,
you're simply flying blind. This is why you need the data sheet.

An ATZ command will reset the modem and an ATH will hang it up. Both
commands are normally sent by DUN in the course of a dial-up session.
I'd suggest that the OP launch a HyperTerminal comms session and send
an ATE1M2L3 command (to enable command echo and turn on the speaker at
max volume) and then send an ATH1 to take the modem off-hook and an
ATH to hang it up. Monitor the voltage at the wall outlet while doing
this. The on-hook voltage should be about 50V and the off-hook volts
should drop to around 10V-20V.

It may also be interesting to see whether the modem is able to pulse
dial, eg ATDP12345678, as this relies on interrupting the loop current
via the hook switch.

Quote:
When you purchase an integrated system, the system designers have
already done this basic bit of homework for you.

The factory settings are restored by an AT&F command.

Quote:
But if you're starting
with the raw chipset, you have to do this bit of research for youself.

Harry C.

I found these documents useful:

"Software Modem and Audio/Modem Riser (AMR) Design"
http://www.eetasia.com/ARTICLES/1999JUN/1999JUN29_BD_NTEK_CT_TAC.PDF

Modem user manual with a chapter on SM56 AT commands:
http://www.modem-help.freeserve.co.uk/download/motorola_sm56pci.pdf

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.
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Don Bowey
electronics forum Guru


Joined: 25 May 2005
Posts: 451

PostPosted: Tue Jun 20, 2006 4:51 pm    Post subject: Re: modem line takeover?! Reply with quote

On 6/20/06 1:48 AM, in article 655e.4497b64b.4af47@clunker.homenet, "jasen"
<jasen@free.net.nz> wrote:

Quote:
On 2006-06-19, Pooh Bear <rabbitsfriendsandrelations@hotmail.com> wrote:


Franc Zabkar wrote:

On 19 Jun 2006 08:44:34 -0700, j_slobo@hotmail.com put finger to
keyboard and composed:

Looked at several Motorola SM56 modems an all have the same fault-non
infinite resistance at line jack which causes them to take over the
line once the line is plugged, so none of the telephones can be used!
Checked the MOV and it is ok and there is no relay on modem !(at least
not a box type, just few too many smd transistors doing smth?)

There is a diode bridge so the line interface is a 'dry transformer'
type.

If there is a transformer, then the DAA is probably dry, as you say.
Otherwise there would usually be two chips, one on the line side and
one on the host side, with two or three ceramic caps providing the
isolation.

The one I have has no relay or transformer.

I'm seeing 19M across the line on the bare pcb.

At 48V ?

Bye.
Jasen

I'm late getting into this, but.....

Have you looked at the documentation for the modem? As a condition of the
Registration program in the U.S., the manufacturer must declare the Ringer
Equivalence for the modem. There are two ways to determine the Ringer
Equivalence Number (REN), and one of them is the Tip to Ring dc resistance.
If they declare REN=2 then the 19M you see may be normal, and is probably
not your problem.

Don
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hhc314@yahoo.com
electronics forum addict


Joined: 11 Sep 2005
Posts: 88

PostPosted: Wed Jun 21, 2006 12:26 am    Post subject: Re: modem line takeover?! Reply with quote

Franc, the USR 56K Faxmodem is also an internal soft modem (new
word?).

All of today's modems have setup switch settings, either hard or soft.
Without these the modem would be relatively inflexible and useless.
It's usually the modem initialization control command that sets them
up, and they typically run from S1 to S7 or more. These determine such
basic things such as if the modem is on-line continuously, normally
off-line, auto-answer, automatic retries, etc. You need to have a copy
of the chipset producer's technical data sheet to learn how to use
them, without which the chipset is virtually useless.

Without knowledge of what these settings mean and how to use them,
you're simply flying blind. This is why you need the data sheet.

When you purchase an integrated system, the system designers have
already done this basic bit of homework for you. But if you're starting
with the raw chipset, you have to do this bit of research for youself.

Harry C.



Franc Zabkar wrote:
Quote:
On 19 Jun 2006 21:34:10 -0700, hhc314@yahoo.com put finger to keyboard
and composed:

My guess is that you're running into the same problem that I originally
had with my USR 56K Fax modem, until I learned how to set its switches.
The problem that I ran into with the SM56 is that the Motorola website
evidently lacks the documentation telling you where to set the switches

That's because there are none. The SM56 is an internal (S)oft(M)odem.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.
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hhc314@yahoo.com
electronics forum addict


Joined: 11 Sep 2005
Posts: 88

PostPosted: Wed Jun 21, 2006 12:30 am    Post subject: Re: modem line takeover?! Reply with quote

What switch settings are you using in your initialization command?

Realize that these are very similar from modem to modem, but not
usually identical. You really need the data sheets for the SM56, which
unfortunately I couldn't find on Motorola's website for some strange
reason.

Harry C.



j_slobo@hotmail.com wrote:
Quote:
Looked at several Motorola SM56 modems an all have the same fault-non
infinite resistance at line jack which causes them to take over the
line once the line is plugged, so none of the telephones can be used!
Checked the MOV and it is ok and there is no relay on modem !(at least
not a box type, just few too many smd transistors doing smth?)
There is a diode bridge so the line interface is a 'dry transformer'
type.Once you disconnect the line and plug it back in, it goes free for
few moments...
What do you suggest I check, other than the optocoupler?( because I
think it has to be ok since the modem is actually working if I manage
to hook to provider in few seconds before it takes over the line)
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