[Asterisk-Users] TDM400P Revision question.

[Rich Adamson]

> 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.
> 

That on-hook AC is a real problem "if" the voltmeter is accuate.

Couple of things to try....

1. Go to the demarc, disconnect the in-house wiring and measure the AC
component again (only looking towards the telco's CO).

2. Disconnect asterisk and install an ordinary analog phone. Take
the phone off-hook and measure the AC. If the value is very small,
then the voltmeter is measuring induced AC on the "unterminated"
wiring. (The phone being off-hook creates the termination.)

Put the phone on-hook and measure again. If the value is large, then
go looking for the source of the induced AC. Things like wall-warts,
fluorescent light ballasts, any device with a transformer in it,
electric motors (of some fairly large size), desktop high intensity
lamps (with internal transformer), etc, can cause inducedAC "if" 
they are within inches of the wiring.

Using a scope would be good, but it will only validate the voltmeter
results; nothing more. If you're unsure about the quality of the
voltmeter, borrow another one from someone and compare the results.