Comms - irritating 'buzz'/'ground' heard by all

techietim

Active Member
Hi All,

We are currently using Tecpro's Master Station MS741 along with BP111 beltpacks and SMH210 headsets (Tecpro Communication Systems)

The problem we are having is that we get an intermittent 'buzz' (what sounds like a connection being grounded) on our Comms and this is sometimes meaning people cannot be heard or their mics stop working for a temporary time.
We've not added any new beltpacks/headsets since this issue and it's causing us lots of problems!
I thought it was my comms connection but new cable, port and headset hasn't fixed the issue!

Does anybody know what might be causing this?
Thanks in advance!

TechieTim
 

Van

CBMod
CB Mods
Premium Member
When you say Intermittent buzz, how intermittent? is it extremely regular? or variable in it's occourence? If it's extremely regular then my money would be on RF interfeerence from a motor, or other inductive load. My immediate thought is a capcitance/ discharge issue somewhere, in a cable, power supply, or in one of the BP's. Intermittent issues are the absolute hardest to pin down because of the nature of the issue. Best way to find it ? Unplug everything all the way down to the base station. then with people on all headset stations, keep hooking things back up until you hear the noise. That will identify the defective run, if it's cable, Pack, if it's a BP, or headest. Once you've isolated the proper Leg start replacing parts; cable, belt pack, headset, a capacitance issue could be hidden in any of them.

Another issue can be capacitance from heat expansion. Do you notice that the buzz isn't there whe you first fire everything up but then after a bit it starts in ? That could simply be a compnent on one pc board in some piece of equipment heating up from the electricity flowing through it. It might have a bad solder to the board and it's expanding and contracting on a microscopic scale as it heats and cools, but it's enough to create an air gap short. If you can locate the offensive piece of hardware you can use freezing spray to cool down individual compnents till you hear the noise stop. sometimes all that is required is a resoldering of the part. < Any of these Steps involving opening up a belt-pack or base station imply that they are being taken by qualified electronics technicians.>
 

FMEng

Well-Known Member
Fight Leukemia
Methodical troubleshooting will reveal the source of the hum. Start by wiggling headset and beltpack cables, especially near connectors. If you can aggravate the buzz by movement, there's the culprit. If not, then remove one beltpack and headset from the system at a time. Do the same for cables. When the system is quiet, that will narrow it down. If it is traced to a beltpack and headset, swap the headset to see if the problems stays or goes away. Chances are you'll find a bad headset cable or a broken connection inside a connector due to a loose strain relief.
 

techietim

Active Member
When you say Intermittent buzz, how intermittent? is it extremely regular? or variable in it's occourence? If it's extremely regular then my money would be on RF interfeerence from a motor, or other inductive load. My immediate thought is a capcitance/ discharge issue somewhere, in a cable, power supply, or in one of the BP's. Intermittent issues are the absolute hardest to pin down because of the nature of the issue. Best way to find it ? Unplug everything all the way down to the base station. then with people on all headset stations, keep hooking things back up until you hear the noise. That will identify the defective run, if it's cable, Pack, if it's a BP, or headest. Once you've isolated the proper Leg start replacing parts; cable, belt pack, headset, a capacitance issue could be hidden in any of them.

Another issue can be capacitance from heat expansion. Do you notice that the buzz isn't there whe you first fire everything up but then after a bit it starts in ? That could simply be a compnent on one pc board in some piece of equipment heating up from the electricity flowing through it. It might have a bad solder to the board and it's expanding and contracting on a microscopic scale as it heats and cools, but it's enough to create an air gap short. If you can locate the offensive piece of hardware you can use freezing spray to cool down individual compnents till you hear the noise stop. sometimes all that is required is a resoldering of the part. < Any of these Steps involving opening up a belt-pack or base station imply that they are being taken by qualified electronics technicians.>

Hey Van,
Your point about the RF interference is probably the cause actually because we've only had this problem on this show were we are using 18 new radio microphones!
Thanks for the advice on pinning down the cause.
The buzz happens for about 20secs every 3-5 minutes.

Thanks for your help!!
-TechieTim
 

techietim

Active Member
Methodical troubleshooting will reveal the source of the hum. Start by wiggling headset and beltpack cables, especially near connectors. If you can aggravate the buzz by movement, there's the culprit. If not, then remove one beltpack and headset from the system at a time. Do the same for cables. When the system is quiet, that will narrow it down. If it is traced to a beltpack and headset, swap the headset to see if the problems stays or goes away. Chances are you'll find a bad headset cable or a broken connection inside a connector due to a loose strain relief.

Hey FMEng,

Thanks very much for the advice - if the buzz persists after this show then we'll look at doing this!

Thanks very much!
-TechieTim
 

Chris15

CBMod
CB Mods
Premium Member
Departed Member
The UK has just been throught the digital switchoff, conveniently timed to happen just before the olympics...

I would not rule out a new user of the 700 MHZ spectrum starting to come online...
 

techietim

Active Member
One "dumb thing" to check is cell phones next to comm packs/lines ;-D

Yeah! The DSM did pretty much shout to everyone on the circuit to check their phone location - mine was sat 1m away on another chair! :lol:
 

techietim

Active Member
Interesting the op says it is a regular interval. Sounds almost like a system that only powers up every now and the. Unfortunately it could be something like a security system, fire alarm etc.
It's only just started so unlikely thanks for the heads up anyway!
 

techietim

Active Member
The UK has just been throught the digital switchoff, conveniently timed to happen just before the olympics...

I would not rule out a new user of the 700 MHZ spectrum starting to come online...

Hey GCPSoundLight,
Good point! Our comms system does ocasionally pick up Asian radio from the local area, so the new user of the 700MHZ frequency is not that unlikely! :(
At one point the comms system company did say that it was the metal beams on our flying grid not being earth was turning the theatre into some "weird reciever thingy" (words of the SM team)..could this be a likely cause?
 

Van

CBMod
CB Mods
Premium Member
...At one point the comms system company did say that it was the metal beams on our flying grid not being earth was turning the theatre into some "weird reciever thingy" (words of the SM team)..could this be a likely cause?

Structure can create a free floating antenna, but from your description of the issue it really sounds to me like an HVAC damper motor, an RF discharge from a Flourescent Ballast, Or possible one of the free floating component issues I mentioned above.
 

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