Help with troubleshooting intercom problem

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Old 02-02-11, 06:55 AM
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Help with troubleshooting intercom problem

I'm in the process of replacing an M&S 2000 intercom system. The new manufacturer's replacement system is compatible with the 4-wire wiring to the room stations, however, after hooking up the new system (which included master , new room stations and door station), the doorbell and radio work fine in all stations, but the voice/talk is low volume and distorted if you turn up the volume at all stations including the master. The system that was removed had an audio failure where there was no sound at all from doorbell or talk despite the light indicators on each station working as though the unit was fine. We assumed the M&S brain was 'dead', but could this be a 'short' causing a similar problem with the new unit. The installer is going to bring out another master to swap and check, but I thought it would be good to have a plan to troubleshoot just in case. Again, the doorbell and radio are working fine with the new system. We did run Cat wire directly between the new master and one of the room stations with the same resulting audio problem. Would a 'short' have created a persistent problem? Also, the master had to be located in a bedroom closet (that's where all the wiring for the 2000was home-run) where there is flourescent lighting. I read somewhere that this could cause a buzz or hum. I assume that it would not cause volume loss? Thanks,
Alan
 

Last edited by tigerose01; 02-02-11 at 06:57 AM. Reason: clarification
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Old 02-03-11, 05:02 AM
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Welcome to the forums.

Shorted wiring could cause the problem. The only way to check is to pull all of the wiring off the stations & master and check each set of wires. Also check to make sure nothing is cross-wired, and there are no shorts between any of the four wires.
 
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Old 02-04-11, 05:33 AM
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master bench-tests bad

Thanks. Turns out the master unit bench-tested bad- question as to whether a short could have caused it still exists I suppose. The replacement will be hooked up one unit at a time to look for any wire problems. thanks
 
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Old 02-05-11, 04:35 AM
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It is entirely possible that the wiring caused the new unit to fail. Connecting one at a time won't ID the problem -- it could damage the replacement.

Checking for shorts is simple. Use an ohm meter or digital multimeter set to ohms x1. Pick a cable at the master end. Put one meter lead on Wire #1 and check it against wires 2, 3, and 4. If the meter shows anything other than zero (or maybe one or two) ohms on any of the wires you've found your short. If not, put the lead on wire #2 and check it against 3 & 4, then put the lead on 3 and check it against 4. Do this for every cable.
 
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