[Asterisk-Users] Channel bank problem via long cable

[Bonzo Armstrong]

I've got a Digium TE405P feeding three Carrier Access AB-II units located
in three separate suites of the complex my company resides in.  I've had
one AB-II connected over about 15' of cable and running for several
weeks now, and it seems to be perfectly happy.

Over the weekend, I added two more AB-IIs, one in each of the other two
suites.  The second unit is about 150 cable feet away from the switch
and it syncs up just fine, but the third is 400 cable feet away and is
having problems with its T1.  The dip switches on all three units are
set the same, and with the exception of the LBO they're all configured
the same in zaptel.conf, yet the furthest AB-II is showing errors.

I've swapped AB-IIs between positions to no effect;  whichever unit
is in the furthest suite cannot fully sync.  There are at least two
cables available in each segment of the run between the far AB-II and
the switch (due to the way our complex is wired, the run is a total of
three in-wall cables and four patch cables), and I have tried them all.
I have also tried plugging into other ports on the TE405P.  I've tried
changing the signalling and the framing.  I've tried changing the LBO
value to everything from 0 to 4.  Through all this, the constant appears
to be that any AB-II placed 400' away from the switch will not behave.

When initially connected, the led next to the T1 jack on the AB-II blinks
yellow a few times, then turns green for at most a quarter second and
then to solid yellow where it stays.  The other status led on the AB-II
for the span stays a solid green.  Picking up a phone connected to this
unit gets me a very noisy dialtone.  If I dial a single digit to get
rid of the dialtone, I hear a pretty steady buzzing noise where there
should be silence.

The curious thing here is that if I use this phone to dial another
extension, 1) there is no problem dialing and 2) if I use a station that's
working properly to listen to the voicemail message, I hear a perfectly
clear signal with just a hint of that same buzzing in the background.

My zaptel.conf looks like this:

span=1,1,0,d4,ami
span=2,1,0,d4,ami
span=3,1,4,d4,ami
fxoks=1-16
fxoks=17-24
fxoks=25-48
fxoks=49-72

Can anyone tell me what I'm missing or what else I might try?  Thanks
in advance.