ClearCom wall inputs not working

ChrisO

Member
Hi there,

I have a rather large 4-channel ClearCom system with 20+ wall inputs. It looks like the "A" channel splits off to 3 areas from the MS-440 base station: booth, backstage, and catwalks/FOH. None of the catwalk stations work - no mic sound, call light, etc. I've looked at all of the wiring in the booth rack (where the base station lives) and in the amp racks (where the catwalk/FOH run appears to branch out) and I can't see anything obviously disconnected.

Some additional context:

-None of the wall inputs or speaker stations for channels "B" or "C" seem to work. The base station indicates a short on channel "B". I don't think it's an issue with the base station, since those channels work fine if I bypass the hard-wired house system and plug directly into the base station. Fixing these is lower priority, but I wonder if it's connected to the channel A issue.

-There's an RS-440 remote station in the system, using the second set of outputs from the base station. This was disconnected when I started here a few months ago. I tried adding it back in, and it shorted out channels "A" and "D". I'm assuming something is wrong with the remote station. It's not particularly integral to the system.

Any thoughts on how to continue troubleshooting? I've opened up most of the wall input boxes and haven't found anything that looks wrong. I'm guessing there's some sort of break in the line between the base station splitter and the amp racks, which are quite far apart. Any advice on what I should be checking with a multimeter would be super helpful. Thanks!


Here's the initial split at the base station. I'm open to suggestions for cleaning this up.
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The inside of the booth rack. I temporarily disconnected the base station to take this photo, since you can't open up the rack when it's connected.
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Inside the amp rack, above balcony seating by a followspot position. 4 of the XLR jacks pictured are for channels A-D, I'm assuming they split off at the bus bar (?) below. The highlighted spot seems odd, I'm not sure why one of the XLR lines would just "dead end" on that bar. Is that a sign that something might have been disconnected at some point?

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Troubleshooting intercom is all about being methodical. You will want a multimeter and a cable toner/tracer.

For starters, I would trace down the problem on Channel B. It'll be easier to find and may be related to the Channel A problem.

Disconnect all beltpacks and portable cables. Test for a short on Channel B's cabling. If the problem went away, the short is likely in a portable XLR cable and wiring in the wall is probably fine.

Then I would open up all of your intercom panels/plates and perform a visual inspection of the cables and terminations. There could be a foil shield shorting to something or one of the wires shorting to another. Where the cables exit the conduit, it's common to find the conduit burrs have cut into the wiring. Keep an eye out for that. If a termination is suspect, cut it and reterminate with a soldering iron. Look for where the cable jacket ends -- someone may have cut too deeply with cable stripper and nicked the conductor installation causing the short. Do a similar inspection of all terminal strips -- the cable management at some of those looks awful and it's possible a conductor or cable was pulled straight out of the terminal. It's also possible a crimp on one of those terminals is bad or that a terminal screw isn't screwed down fully.

After inspecting the connectors, and go to the terminal strips and start disconnecting the various branches of wiring. Use the wire numbers if you have any on the cables and/or put the cable tracer on them to find out where they go. One by one, tag the cables so you know which ones go where, and test the branches for with a multimeter (continuity test between pins 1/2, 2/3, 1/3, and 1/conduit ground, 2/conduit, 3/conduit). If the cabling is in good order, you should not have any continuity here. If your meter beeps, you know you have a problem. If any of the conductors are shorted to each other, you likely have a problem at a connector plate. If they're shorted to conduit ground, somewhere the cable got skinned and is in contact with conduit/back boxes/etc.

If you haven't found obvious causes yet, then you need to identify the suspect cables and follow their conduits and see where they go. Open junction boxes and look for cables tightly pulled against conduit edges. Look for areas where conduit may have been damaged or cut by a previous project. If you find the cabling is suspect but cannot find the issue with the cable, then it's time to buy some wire and use the existing cabling as a pull string to pull new wire in through the existing conduits and reterminate.

Through the process of tagging which wires go where, you should have a clear diagram of what your cable topology is. That'll let you know if something's miswired at a terminal strip. You're looking for a needle in a haystack and may have 10 different minor issues that add up, or 1 really major issue that's causing all of your channels to short out (such as someone inadvertently landed the Channel A and Channel B feeds on the same barrier strip tied together. The only real way to solve complicated intercom issues is through a slash-and-burn approach where you test everything to rule branch wiring out by process of elimination until you get a clearer picture of what the precise source of the problem is.

===

Troubleshooting steps aside, you need to think outside the box about what could've happened. At one renovation project there were a number of mysterious symptoms. Through tracing things out, disconnecting and reconnecting branches, and following the conduits, we discovered one of the conduits went down within a block wall and a suspiciously new device mounted on the wall. When the facilities guys mounted their new device in the scene shop, they drilled through the block and hit the conduits within, twisting the cabling with their drill bit and shorting 70V speaker feed to the dressing rooms to conduit ground, which was then inducing their backstage audio feed into the intercom cabling. Then they got out of Dodge without telling anyone they had hit this conduit. In an older system, that wasn't the only issue, but it explained why they were complaining of hearing their backstage dressing room audio in their intercom. Several wall plates also had shorts and previous attempts over the years to fix things at the terminal strips meant the terminal strips were a nightmare and Channel B from a given wall plate could very easily be landed on a Channel A terminal.

Don't be afraid to get creative. You can disconnect Channel A from the Main Station, put your toner on terminals for Channel A, and walk around the venue to all the plates and confirm Channel A is ending up where you think it is.

It's also helpful to have 1-2 people with you and a set of radios (or cell phones if you have decent coverage). This goes fastest when you have one person messing with terminal strips and another walking around with a multimeter, tracer wand, and a screwdriver.
 
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One other languishing thought. Open every XLR permanently wired into the system. Systematic issues like failure at the remote station could be a faulty wiring within the XLR’s. If someone stripped the wires too far back or miswired something on one connector, there’s a decent chance they did the same thing on others. If in doubt, pull the RS440 and plug it into the MS with known good XLR cables and see what happens. If it still dies, it could indeed be a faulty station, but if it works you know you have a cabling problem.
 
Thanks! This is super helpful. I started to dig in between band concert setups, and found some interesting things-

-The remote station works fine when it's plugged directly into the main station (bypassing building wiring). The XLRs running into the remote station have 2 cables in each connector, and one of them looked like it might have a black/ground short, pictured below. (Some e-tape as a quick fix didn't change anything). Should I redo these connections with heatshrink, or is there a better alternative to these 2-in-1 XLR connectors?
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-Many of the grounds are tied together as pictured below, outside of any connector. Would this cause a short if it touched anything metal in a rack or conduit box?
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-The intercom system is tied into our 1/4" patch bay for headset extensions, program in, etc. Could bad inputs on the patch bay potentially contribute to these issues?

Again, thanks a bunch for your help!
 
Thanks! This is super helpful. I started to dig in between band concert setups, and found some interesting things-

-The remote station works fine when it's plugged directly into the main station (bypassing building wiring). The XLRs running into the remote station have 2 cables in each connector, and one of them looked like it might have a black/ground short, pictured below. (Some e-tape as a quick fix didn't change anything). Should I redo these connections with heatshrink, or is there a better alternative to these 2-in-1 XLR connectors?
View attachment 22707

-Many of the grounds are tied together as pictured below, outside of any connector. Would this cause a short if it touched anything metal in a rack or conduit box?
View attachment 22708


-The intercom system is tied into our 1/4" patch bay for headset extensions, program in, etc. Could bad inputs on the patch bay potentially contribute to these issues?

Again, thanks a bunch for your help!
@ChrisO Analog (Pre Digital) Clear Com basics.
With EVERYTHING; stations, belt packs, and cables unplugged from your building wiring:
Using an ohm meter, or continuity beeper, All contact #1's should connect to each other.
NONE of your contact #1's should contact ground.
The entire system should be grounded at one, & ONLY one, point via the ground pin on the power supply's mains connector when it's plugged in.
All contact #2's should connect to each other and NOT to ground.
All contact @3's should connect to each other and NOT to ground.
All in wall wiring should be 18 gauge shielded pair, Belden 8760 or equivalent.
This should give you a good starting point and occupy a few hours. Please keep us posted.
Toodleoo!
Ton Hebbard
 
Re: Remote Station, it looks like they heated the wire too hot when soldering the terminations, melting the insulation on the conductors, allowing them to short together. Generally, this is a "new guy" issue where the same person will do a lot of the terminations, and if you find one termination bad there's a good chance others will be too. It's probably worthwhile looking for similar failures or signs of melted wire insulation before you go to the more extreme troubleshooting methods.
 
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Following up on this - I found a solution to bring pretty much all of Channel A back to life. Not so much a "fix"...rather a "workaround that solved some issues"

Our 1/4" patch bay has an assortment of intercom extension ports, which can be patched over to XLR mic inputs throughout the theatre. There's a mic input right next to one of the bad Channel A port, so I patched that into the intercom extension and then simply ran an XLR cable from that mic input straight into the existing Channel A port. Sure enough, all of the overstage ports work again, including (importantly) our followspots. It does feel kinda weird to be routing the IC send back into itself. But there's a lot of conduit that I can't access, so I wouldn't be surprised if the line is fully broken somewhere and I've simply bypassed it with this workaround.

Thanks again for everyone's help on this. It'll be really helpful when I get a chance to dive deeper into the issues with channels B-D.
 

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