modem line takeover?!

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)

Reply to
j_slobo
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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.

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

Reply to
Pooh Bear

Nope and I doubt I will be able -it's just too tiny!

Reply to
j_slobo

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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Reply to
default

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

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

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.

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

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Reply to
Franc Zabkar

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

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

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Reply to
Franc Zabkar

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

Reply to
Pooh Bear

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 snipped-for-privacy@hotmail.com wrote:

Reply to
hhc314

}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.

Reply to
Stan

At 48V ?

Bye. Jasen

Reply to
jasen

On Tue, 20 Jun 2006 00:48:22 +0100, Pooh Bear put finger to keyboard and composed:

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

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Reply to
Franc Zabkar

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

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

- Franc Zabkar

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Reply to
Franc Zabkar

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

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.

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

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.

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.

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

I found these documents useful:

"Software Modem and Audio/Modem Riser (AMR) Design"

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Modem user manual with a chapter on SM56 AT commands:

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- Franc Zabkar

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Reply to
Franc Zabkar

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

Reply to
Don Bowey

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:

Reply to
hhc314

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 snipped-for-privacy@hotmail.com wrote:

Reply to
hhc314

Just as an afterthought, Motorola does have some downloadable SM56 drivers on their website. It's quite possible that these will do the modem setup for you....and certainly worth a try.

Harry C.

j snipped-for-privacy@hotmail.com wrote:

Reply to
hhc314

The box contains a driver CD, a leaflet like 'manual' with none of that info, a piece of foam plastic and the pcb in an anti-static bag.

The pcb has TUV, CE and FCC ( but not an FCC id ) printed on it together with what I originally took to be the BABT approvals symbol ( but possibly isn't ).

I suspect the above are bogus.

There's no manufacturers info anywhere but I recall that it was sold as 'Mentor' brand.

I've an idea to report this. Maybe I'll give the company that sold it a chance to replace it though ?

Graham

Reply to
Pooh Bear

There's a WO series 1 amp bridge on the line.

I'll check that when I get a sec.

Graham

Reply to
Pooh Bear

Eh ? My SM56 was sold to me as a retail PCI modem.

Motorola no longer make that chip anyway and indeed Motorola's not into selling semis at all any more ( it's On Semi and Waferscale ? now )

Graham

Reply to
Pooh Bear

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