[Asterisk-Users] TDM400P Revision question.

[Ian Pattison]

My specific issue has to do with ringing on my FXS ports.

A Northen Telecom Harmony phone (circa 1983) rings normally but when I connect my newer GE 2.4GHz cordless I never get more than 1/2 ring (it lights up and works fine... just can't get a ring from it). Normally I'd assume that it's a low power issue on the FXS port but with a phone rated at 0.1 REM?

I do have some strange voltages though....

ON-Hook: ~48V DC, 107V AC (this really concerns me...)
Off-hook: ~6V DC, ~12VAC (where the hell is this AC component coming from???)
Ring: 0V DC, ~45V AC

Suffice it to say that electrically this is completely out to lunch... I'd like to throw an oscilloscope on the line to see what's what but I'm having trouble finding one.

Thanks,

Ian
>>> radamson at routers.com 14/04/2005 10:14 >>>

> > > I was following a discussion on this list about the TDM400P 
> > revisions. 
> > >It is my understanding that the current revision that one 
> > should have 
> > >is the Rev. H and not the E/F. I have not yet been able to 
> > verify the 
> > >rev stamped on the board, but zaptel is reporting that I 
> > have the Rev. 
> > >E/F. I just bought this card in January direct from Digium and was 
> > >wondering if I got the wrong Rev.
> > >somehow?? I have been having some intermittent problems but only 
> > >thought it was my setup.
> > > 
> 
> 
> 
> I did some more testing today. I called Digium on 4/12 and they
> suggested some things to try, like different motherboard, switching pci
> slots, etc.. I did everything they asked, except for the mother switch
> as I do not have a different one to put in the system at this time.
> 
> So, after all that, my ringing issue still persists. Too some
> measurements from bot the card and my POTS line in both the on-hook
> state and ringing state. I uses a digital multi-meter to make the
> measurements on both. Here are the results....
> 
> TDM400P
> 
> Before slot change:
> 
> On hook idle:
> 
> 43.8 Volts DC
> 0    Volts AC
> 
> Ringing:
> 
> 0    Volts DC
> 56.4 Volts AC
> 
> After slot change:
> 
> On hook idle:
> 
> 48.7 Volts DC
> 0    Volts AC
> 
> Ringing:
> 
> 0    Volts DC
> 65.5 Volts AC

We can only assume the above represents a fxs module on the
card. Correct?

I would find it hard to believe that changing slots would cause
the on hook DC voltage to change from 43v to 48v. That smells like
a funcky voltmeter. Slots should have nothing to do with DC
voltage unless the module is simply bad. The AC (ringing) voltage
is reasonable, but again it should not have changed simply
because of a slot change; again, questionable voltmeter.
 
> On my POTS line:
> 
> On hook idle:
> 
> 43.8 Volts DC
> .013 Volts AC
> 
> Ringing:
> 
> 50.5 Volts DC
> 93.9 Volts AC

The on hook DC voltage from all US telco's will factually be
in the 48v to 52v range. If their central office equipment produced
43 volts, they would have alarms going off all over the place.
Their alarms would trigger somewhere in the 46 to 48 volt range.
So, that measurement implies the voltmeter is not accurate.
The AC (ringing) voltage is well within acceptable telco limits
and can range from about 70v to upwards of 105v.
 
> Could it bee that from the phone company they retain the DC offset
> voltage while applying a ring frequency and as it appears on the TDM it
> shuts off the DC offset when ringing starts. Could this be the issue
> with those of us in the U.S. having ringing issues with the TDM's??

Doubtful that is an issue. The reason for saying that is the chipset
used on the fxo & fxs modules was manufactured by Silicon Labs, and
those same chipsets are used in other telephony equipment worldwide.
Silicon Labs is known for good to excellent products. If their chipsets
didn't function correctly, there would have been a large uprising a
couple of years ago when those chips were first produced. That
hasn't happened, and they don't have a lengthy chip revision history.

Asterisk code does not have any control over adding/removing the DC
component during ringing, so that's not an issue either. Doubtful
that adding/removal the DC component would have any impact on 
normal telephone sets, however there certainly could be funcky sets
that don't like that DC removal.

Given the number of postings relative to the TDM card lately, I don't
remember exactly what your ringing issue was. Could you remind us
without deleting the significant parts of the above?


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