DuKane School Intercom

R

RootBoy

Guest
I have a school intercom, a Dukane MACS II system that has a problem.
Two class rooms where added and in one of the class rooms only the
office can call in to the room but the teacher cannot be heard. All
other classrooms work fine. I have test all the wires and replaced all
the parts and swaps channel at the PA, and no change.
Can someone explain why the VOX doesn't work with this one classroom.
Also what activates the switching of the VOX system at the ACS
(console unit).
Thanks
RBS
 
I am going to "guess" because I am not familiar with the particular
unit. But if there may be a form of "anti-vox" circuit so that while the
office is talking, the classroom VOX won't activate. So if there is any
form of noise on the wiring, the anti-vox is activated. You did use
balanced, twisted pairs for the wiring? Maybe one lead is shorted to
ground. Is there any noticeable hum or buzz? Dis you swap the units in
the classrooms? Could also be a level or sensitiviity problem.

RootBoy wrote:

I have a school intercom, a Dukane MACS II system that has a problem.
Two class rooms where added and in one of the class rooms only the
office can call in to the room but the teacher cannot be heard. All
other classrooms work fine. I have test all the wires and replaced all
the parts and swaps channel at the PA, and no change.
Can someone explain why the VOX doesn't work with this one classroom.
Also what activates the switching of the VOX system at the ACS
(console unit).
Thanks
RBS
Click to expand...

--
Joe Leikhim K4SAT


"Jazz is not dead. It just smells funny." -F.Z.
 
In article <7h2lpvk36oumu25bn7e7eorsv5hqfpip3t@4ax.com>,
rootboyslimy2k@yahoo.com says...
I have a school intercom, a Dukane MACS II system that has a problem.
Two class rooms where added and in one of the class rooms only the
office can call in to the room but the teacher cannot be heard. All
other classrooms work fine. I have test all the wires and replaced all
the parts and swaps channel at the PA, and no change.
Can someone explain why the VOX doesn't work with this one classroom.
Click to expand...
Exactly how were the two new rooms added? They must be home
runs, and must use 70V (or 25V) speakers. More details on
what you have, and have done, would be helpfull.

Also what activates the switching of the VOX system at the ACS
(console unit).
Click to expand...
IIRC, the master uses VOX only in an off-hook state, in
which case it's simple audio sense/switch. If the master is
being used hands-free, it's PTT.
--
Mark

The truth as I perceive it to be.
Your perception may be different.

Triple Z is spam control.
 
Thanks for the responses.
The classrooms are in a mobile unit install over a year ago.
The two cables where install from the main office to the
Mobile unit with no splices and are aprox. 450 feet long.
The cable is four conductor with shield. The white and shield
Are connect to the normally open call button and the black and red
are connected to the speaker, 70V, and lowest wattage tap.
I have used a meter to check for any shorts or grounds there are none.
Both cables test the same. In one room the system works, the other
room does not.
I have swapped the speaker and used different combinations of wires
including the green that is a spare. The results are the same.
Iswapped connects at the head end to a known good input and the same
results. The office gets the call from the classroom
and answers. The teacher in the classroom can hear the secretary but
the secretary cannot hear the classroom, no background noise, nothing.
All calls are made and answered with the receiver off the hook.
Thanks again for the help.
RBS

On Sat, 25 Oct 2003 17:49:26 -0400, Mark <ZZZmark@whiskey-creek.net>
wrote:

In article <7h2lpvk36oumu25bn7e7eorsv5hqfpip3t@4ax.com>,
rootboyslimy2k@yahoo.com says...
I have a school intercom, a Dukane MACS II system that has a problem.
Two class rooms where added and in one of the class rooms only the
office can call in to the room but the teacher cannot be heard. All
other classrooms work fine. I have test all the wires and replaced all
the parts and swaps channel at the PA, and no change.
Can someone explain why the VOX doesn't work with this one classroom.

Exactly how were the two new rooms added? They must be home
runs, and must use 70V (or 25V) speakers. More details on
what you have, and have done, would be helpfull.

Also what activates the switching of the VOX system at the ACS
(console unit).

IIRC, the master uses VOX only in an off-hook state, in
which case it's simple audio sense/switch. If the master is
being used hands-free, it's PTT.
Click to expand...
 
In article <msgmpvkv8egqojn8lfn1eipocvb46tmkhl@4ax.com>,
rootboyslimy2k@yahoo.com says...
Thanks for the responses.
The classrooms are in a mobile unit install over a year ago.
The two cables where install from the main office to the
Mobile unit with no splices and are aprox. 450 feet long.
The cable is four conductor with shield. The white and shield
Are connect to the normally open call button and the black and red
are connected to the speaker, 70V, and lowest wattage tap.
I have used a meter to check for any shorts or grounds there are none.
Both cables test the same. In one room the system works, the other
room does not.
I have swapped the speaker and used different combinations of wires
including the green that is a spare. The results are the same.
Iswapped connects at the head end to a known good input and the same
results. The office gets the call from the classroom
and answers. The teacher in the classroom can hear the secretary but
the secretary cannot hear the classroom, no background noise, nothing.
All calls are made and answered with the receiver off the hook.
Thanks again for the help.
RBS
Well, that is a tough one. You've done all the right things
Click to expand...
to troubleshoot, and it sounds as if the rooms have been
added correctly.

My hunch is that one of the audio pair to that trailer
(red/green) is shorted to Earth, NOT necessarily to shield.
It has probably occurred where the cable enters the skin of
the trailer, but could be in the main building as well.

Since the trailers are probably in close proximity, get
ahold of any two-conductor (even an extension cord would
work temporarily) and with some jumpers, connect the "bad"
speaker to the audio pair of the "good" speaker in the other
trailer. If you get two-way audio, you'll know you need to
pull new 357 to the "bad" trailer.

Another alternative, since this is configured as a three-
wire system, is to substitute the green wire at BOTH ends
for the red, then the black, and see if that resolves the
issue. If it works, you may be able to leave it that way if
the noise level isn't too high, as the green is unshielded.

.....

Just had another thought. You said you checked for shorts,
but did you check for opens? Disconnect both red/green at
both the speaker and the head end. Read across them from
either end, you should get infinite Ohms (if not, they're
shorted somewhere). Now twist one end together and read
across them from the other end, you should get something
less than 10 Ohms. If not, obviously an open conductor.
The most likely place will be at the splice in the trailer,
which should be either at the switch or at the speaker.

And yes, it is still possible to get some one-way audio on a
system such as this with one conductor open.

--
Mark

The truth as I perceive it to be.
Your perception may be different.

Triple Z is spam control.
 
RootBoy wrote:

Thanks for the responses.
The classrooms are in a mobile unit install over a year ago.
The two cables where install from the main office to the
Mobile unit with no splices and are aprox. 450 feet long.
The cable is four conductor with shield. The white and shield
Are connect to the normally open call button and the black and red
are connected to the speaker, 70V, and lowest wattage tap.
I have used a meter to check for any shorts or grounds there are none.
Both cables test the same. In one room the system works, the other
room does not.
I have swapped the speaker and used different combinations of wires
including the green that is a spare. The results are the same.
Iswapped connects at the head end to a known good input and the same
results. The office gets the call from the classroom
and answers. The teacher in the classroom can hear the secretary but
the secretary cannot hear the classroom, no background noise, nothing.
All calls are made and answered with the receiver off the hook.
Thanks again for the help.
RBS

On Sat, 25 Oct 2003 17:49:26 -0400, Mark <ZZZmark@whiskey-creek.net
wrote:

In article <7h2lpvk36oumu25bn7e7eorsv5hqfpip3t@4ax.com>,
rootboyslimy2k@yahoo.com says...
I have a school intercom, a Dukane MACS II system that has a problem.
Two class rooms where added and in one of the class rooms only the
office can call in to the room but the teacher cannot be heard. All
other classrooms work fine. I have test all the wires and replaced all
the parts and swaps channel at the PA, and no change.
Can someone explain why the VOX doesn't work with this one classroom.

Exactly how were the two new rooms added? They must be home
runs, and must use 70V (or 25V) speakers. More details on
what you have, and have done, would be helpfull.

Also what activates the switching of the VOX system at the ACS
(console unit).

IIRC, the master uses VOX only in an off-hook state, in
which case it's simple audio sense/switch. If the master is
being used hands-free, it's PTT.
Click to expand...
1# To test 70 volts lines, your need an IMPEDANCE meter and NOT
a DVM. AN i impedance meter puts an AC signal down the line to test
its AC load. Some (like a TOA ZM104, use a 1000 HZ tone than can be
used as a trouble shooting too by listening to the speaker.

There are basically two kinds of intercom. Annunciator and non Annunicator.
On a annunciator unit, pressing the classroom button lights a light on the
main console on which room it is that's calling. On a non annunciator unit,
any class
room can call in, but there is no ID at the main console. They have to say
"its room 205" or such. Then room 205 has to be manually selected at the
main console. If its NOT manually selected, the office will NOT be heard in
the class room.

What i would do is remove the speaker and take it into the office close to
the main unit and temporarily wire it in. trouble shoot it from that point.
Does it work now? if it does, you have a wiring problem. IF not, your
either not hooking up the correct terminals on the main unit, or the main
unit
has a problem or is NOT internally configured for that many stations.
If you had a Toa ZM104 you could put a 1000 HZ tone down the line from the
office, listen to the tone in the classroom to verify the wiring, and do a 70
volt line load check at the same time. If you do this kind of work, its
highly recommended.

BOB



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Thanks for the help.
There was water in the underground
conduit that connects to the mobile
classroom to the main school building.
Water migrated in to the cabling creating a
high impedance that placed the classroom
In "privacy mode". Replacing the last portion
of cable in the conduit and under the mobile
classroom fixed the problem.
Thanks again,
RBS




On Sun, 26 Oct 2003 08:46:00 -0600, BOB URZ
<"sound(remove)"@inetnebr.com> wrote:
 
On Sun, 02 Nov 2003 11:04:31 -0600, RootBoy <rootboyslimy2k@yahoo.com>
wrote:

Thanks for the help.
There was water in the underground
conduit that connects to the mobile
classroom to the main school building.
Water migrated in to the cabling creating a
high impedance that placed the classroom
In "privacy mode". Replacing the last portion
of cable in the conduit and under the mobile
classroom fixed the problem.
Thanks again,
RBS
Click to expand...
How do you determine that there was high impedance? Replaced the
conduit? Hope you do want no water there or you'll be there again
next year.

Cheers,

Wizard
 
Checked the cable with a DVM but a a higher range (resistance), the
DVM is not auto ranging. After I replaced the cable I physical
inspected the old cable and found water in the cable and the shield
was blacken.
The new cable is a temp fix, new direct burial cable is on the way,
this should fix the problem.
Looking into getting a impedance meter.
Thanks
RBS

On Sun, 02 Nov 2003 21:24:18 GMT, jpero@sympatico.ca (Jason D.) wrote:

On Sun, 02 Nov 2003 11:04:31 -0600, RootBoy <rootboyslimy2k@yahoo.com
wrote:

Thanks for the help.
There was water in the underground
conduit that connects to the mobile
classroom to the main school building.
Water migrated in to the cabling creating a
high impedance that placed the classroom
In "privacy mode". Replacing the last portion
of cable in the conduit and under the mobile
classroom fixed the problem.
Thanks again,
RBS

How do you determine that there was high impedance? Replaced the
conduit? Hope you do want no water there or you'll be there again
next year.

Cheers,

Wizard
Click to expand...
 
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