Microphones New Wireless drops out

[Olddean]

It's a mystery.

New (Sept. '09) Audio Technica ATW-702 handheld microphone drops out within a few minutes of beginning of use. It started to do this in the first 2 weeks. Turn off for a while (1/2 hr) and turn it on again and it will work perfectly for a few minutes. Installation is in K-8 school gym/aud.

When drop out occurs, no sound comes from the speakers, but the receiver indicates that it is receiving a signal from the microphone.

At the same time that the wireless microphone system cannot produce sound, a hard wired microphone connected through the mixer functions normally. I have switched inputs into mixer channels and see no change.

I dusted out the amplifier about one month into the mystery. It worked better for about 6 weeks, then reverted.

Batteries are good.
Mixer is 10 years old: Behringer Eurorack MX802A.
Amp is 5 years old: QSC RMX1450.

It seems like the receiver is getting overheated. Possible?

Mixer, Amp and receiver are all contained in a cabinet. I thought the amp might not be getting enough circulation of air, so added an 8" x 8" vent in the cabinet door directly in front of the amp air intake. No effect.

I will be happy to try any suggestions. A sales rep visited and of course the problem couldn't be made to occur.

Thanks for your help.

OldDean, reluctant sound fixer

 

[BillESC]

A few questions may help.

How far from the receiver is the mic being used?

Is the receiver in a metal cabinet?

Have you tried replacing the cable from the receiver to the mixer?

 

[Olddean]

Thanks for your quick response.

Microphone is used throughout the gym, but usually about 50 feet from receiver. Working or not working doesn't seem to have anything to do with distance. Once it stops working it doesn't matter how close microphone is to receiver.

The cabinet is chipboard cheapie from Home Depot.

Early on I replaced the cable from receiver to mixer. Haven't done that lately. I will try it.

Thanks again,
OD

 

[SHARYNF]

It looks like temperature related. I could be problems like the Xbox has where either the heat or lack of heat causes one of the surface mounted devices to loose its connection to the pcb. I'd send it back for repair/replace

Sharyn

 

[aemeeich]

Where are you located? What tv stations are nearby? And what is their actual transmitting frequency?

What I think is happening is interference from a tv station in your area. I had the same problem as you are having a couple of years ago when I first bought some AT 3000 series systems at the high school I am TD at. I didn't coordinate frequencies to avoid using the frequencies that my local tv stations were broadcasting on (I didn't know any better at the time). Every once in a while, I would stop getting sound out of the reciever. The display would indicate AF levels and RF levels, but the alert light was on, and there was no sound. I was completely stumped for about a year and a half before I learned about frequency coordination. I have a packet all typed up with all the available frequencies for my wireless systems, with the frequencies my local TV stations operate on crossed off. I havn't had a drop out since I did that.

When operating on a frequency that is used by a tv station, the Tone Squelch on the wireless receiver will get activated and cause the audio to lock out.

The 700 series operates on RF channels 26, 27, 28, or 29. If you let me know what city you are in, I can let you know what channels you can't use.

Michael

 

[fredthe]

I agree that it sounds temperature related. As for TV interference, for Stratford, CT, Ch 26 and 28 may have problems.

-Fred

 

[Chris15]

This doesn't sound like an interference issue - you'd notice that the moment it was switched on, and more so when it was switched off - you aren't getting signal on the meters when the transmitters off now are you?

I agree with Sharyn, sound heat related, especially since it's clockwork accurate and resets after a cool down period. It's new you say, send it back for warranty and be done with it.

 

[MarshallPope]

Could it have something to do with it's proximity to the amp and the heat that it produces? How close is the receiver to the amp? Have you tried moving the receiver out of the cabinet to see if that might affect it?

Just an idea, maybe someone with more experience than I will confirm/deny this possibility.

 

[aemeeich]

This doesn't sound like an interference issue - you'd notice that the moment it was switched on, and more so when it was switched off - you aren't getting signal on the meters when the transmitters off now are you?

Not necessarily. The Tone Squelch that AT wireless receivers use will prevent any interference from becoming audible if the receiver isn't receiving the tone from a compatible AT transmitter. From AT's website -

"To help overcome this problem, other more complicated squelch techniques have been developed. One is to add a high-frequency pilot tone to the transmitter signal. The receiver checks incoming signals to see if the pilot tone is present. If not, the receiver assumes that the signal is not from its own transmitter and keeps the receiver muted even if the interfering signal is very strong. This form of squelch is generally referred to as "pilot tone" or "tone coded" squelch."

"700 Series receivers feature a sophisticated Tone Lock™ tone squelch system that opens the receiver's audio output only when a 700 Series transmitter is detected, reducing the possibility of interference. As a result, 700 Series transmitters and receivers must be used together and should not be used with components from other Audio-Technica wireless systems,
or with those of other manufacturers."

If the tone is lost - the transmitter goes out of range, or the signal drops low for a bit - the receiver will mute the audio output, and as I experienced, even if the transmitters were brought right up to the receivers, the squelch would not reopen the audio output. The transmitter needed to be power cycled and it immediately worked again.

Yes it could be temperature related - I have had electronics that overheated within minutes of powering up and stopped functioning - but there are greater odds that it is interference related.

RF 26, 27 and 28 are used by TV stations in the Stratford area
RF 26 is 26-1 WHPX ION
RF 27 is 54-1 WTBY TBN
RF 28 is 4-1 WNBC NBC

That means that frequency channels 1, 2, 3, 4, 5, & 6 should not be used.
(according to the FCC's website, Stratford should be in the fringe areas for WTBY so frequencies 3 & 4 might work for you, but the only safe ones are 7 & 8.)

Olddean - what frequency is the system currently set for? Set it on 7, or 8 and see if you are still getting dropouts.

Michael

 

[SHARYNF]

The thing that makes me look to heat vs interference is that when it is shut off for a half hour it comes back on, SO is it a coincidence that the interference comes and goes away. IMO if it were from a tv station, that would be unlikely since the tv station typically is transmitting all the time, I could be from some sort of other transmitter, that just happens to be working at verious times, like some sort of radio device but again seems to coincidental

The Xbox as I mentioned brought national attention to some of the issues with poorly designed or produced surface mount products when exposed to heat. what happens I believe is that the heat causes the pc board to change shape just enought that the solder connection on part of the surface mount device is broken and therefore fails to work.

I would be interesting to see if rapid cooling would solve the problem

Sharyn

 

[Morpheus]

The thing that makes me look to heat vs interference is that when it is shut off for a half hour it comes back on, SO is it a coincidence that the interference comes and goes away. IMO if it were from a tv station, that would be unlikely since the tv station typically is transmitting all the time, I could be from some sort of other transmitter, that just happens to be working at verious times, like some sort of radio device but again seems to coincidental

The Xbox as I mentioned brought national attention to some of the issues with poorly designed or produced surface mount products when exposed to heat. what happens I believe is that the heat causes the pc board to change shape just enought that the solder connection on part of the surface mount device is broken and therefore fails to work.

I would be interesting to see if rapid cooling would solve the problem

Sharyn

The Xbox part is pretty much on, at least as far as I know.
There are some videos out there explaining how (and why, for reasons you mentioned) you can fix a dead Xbox with a towel!

 

[Olddean]

Many, many, many thanks for all the feedback. Many ideas to examine and ponder. However, after posting here I also bypassed my sales rep, who tried hard to be helpful when I originally experienced problems and sent my inquiry directly to Audio-tech... See response from Audio-Tech:

"Would you please check the serial number prefix of your R700 receiver? We have a recall on our web site for receivers who’s serial number begins with 0924 or 0928. There is a capacitor in the receiver that needs to be replaced due to a manufacturing problem." The recall is dated Sept. 29, 2009.

Indeed, my serial number begins with 0924, which seems to be the answer. I am sure any one of you very helpful people with appropriate experience would have quickly seen that it had to be the receiver. That was my feeling all along... BUT early on in the ordeal the visiting tech assured me that it had to be the old mixer or the old amp.

Anyway, thanks to all -- I hope the problem will be solved -- if you know anybody with a 700 series AT wireless receiver, suggest they check out the recall.

Best, Olddean.