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[Mike Caldwell]

Yes sir, it happened once today. It was about a minute long. I did lose signal lamps on the amp but saw no other indicators that lead me anywhere. I usually am working the power point instead of the sound board but saw no other indicators that suggested anything.

So did the meters on the DSP unit still show full active signal level?

[Billy Snody]

After church this morning I was able to connect to the DSP and view it with the software. WOW, this is neat. (newbie!!!) As one of you suggested, it appears that it is being used as a glorified line level splitter for the most part. Input 1 gain at "0" connected to outputs 1,2, and 3. Output 1 gain at 0, output 2 at 3.75, and output 3 at -21.75. There were 4 FBX points but I didn't alter anything except turning off the Input 2 output to output 2. There is nothing connected to input 2 so I figured it could not hurt anything. I did not notice any change. I ran the volume up pretty good for about an hour. This was after the service and all I had was a cd source I will try switching M to L and or R and see what happens.

[g'bye, Dick Rees]

Next time it happens, forget the lights, bells and whistles and put your hand on the amp.  If it's hot, you're in thermal protect.

All the info you've given and the signs point to thermal shut-down.  Once you either confirm or rule this out then you can proceed further...if needed.

I think you'll find the amp is going into protect as described in the manual on the pages I linked.

[Billy Snody]

Next time it happens, forget the lights, bells and whistles and put your hand on the amp.  If it's hot, you're in thermal protect.

All the info you've given and the signs point to thermal shut-down.  Once you either confirm or rule this out then you can proceed further...if needed.

I think you'll find the amp is going into protect as described in the manual on the pages I linked.

That was my thought pattern when it happened on the original main amp, RMX1850HD. That is also why I removed it from the system and sent it in for a physical. I moved the 1450 into service on the FOH circuit and now am getting the same scenario. This is why I am now exploring the DSP. I figure sooner or later and can remove/eliminate the culprit. I just hope I don't have to figure out how to eliminate the mixer. I am doing all of this without a connection roadmap and am creating one as I go. The mixer has many connections!

[Billy Snody]

Clarksville Texas

[g'bye, Dick Rees]

That was my thought pattern when it happened on the original main amp, RMX1850HD. That is also why I removed it from the system and sent it in for a physical. I moved the 1450 into service on the FOH circuit and now am getting the same scenario. This is why I am now exploring the DSP. I figure sooner or later and can remove/eliminate the culprit. I just hope I don't have to figure out how to eliminate the mixer. I am doing all of this without a connection roadmap and am creating one as I go. The mixer has many connections!

Bill...

There are several common scenarios for amps over-heating.

1.  Lack of ventilation/cooling air, blocked exhaust.

2.  Dirt and dust in the amp interior.

3.  AC power issues, usually under-current.

4.  Shorting speaker cable, poor connection on the output side.

5.  Improper loading of the output.  Possible causes include miscalculation of impedance matching due to amp run in bridge mode instead of stereo.  Inadvertent bridging could also result in connection error with your speaker cables.

The fact that the situation clears itself up after a muted interval points squarely to the thermal issue.  Amp heats up, goes into protect (mutes), cools below protect threshold, etc.  QSC repair may well find no fault in
the  amp if the protect feature is functioning for its intended purpose.  This would indicate that something outside the amp itself is causing the overheating.

There is very little chance that the system processor is at fault.  Highest probabilities are as above:  power and/or cabling, load/mode, connections...you get the idea.  Right now it seems like you're looking for a particular culprit when it may just as well be a configuration, connectivity or power issue.

One thing to consider:  has anything in the building changed lately?  Do any changes (even in the kitchen or physical plant) coincide with the onset of the "muting"?

Good luck.

[Scott Holtzman]

Bill...

There are several common scenarios for amps over-heating.

1.  Lack of ventilation/cooling air, blocked exhaust.

2.  Dirt and dust in the amp interior.

3.  AC power issues, usually under-current.

4.  Shorting speaker cable, poor connection on the output side.

5.  Improper loading of the output.  Possible causes include miscalculation of impedance matching due to amp run in bridge mode instead of stereo.  Inadvertent bridging could also result in connection error with your speaker cables.

The fact that the situation clears itself up after a muted interval points squarely to the thermal issue.  Amp heats up, goes into protect (mutes), cools below protect threshold, etc.  QSC repair may well find no fault in
the  amp if the protect feature is functioning for its intended purpose.  This would indicate that something outside the amp itself is causing the overheating.

There is very little chance that the system processor is at fault.  Highest probabilities are as above:  power and/or cabling, load/mode, connections...you get the idea.

Good luck.

I agree completely with Dick.  I have been lurking in the thread awaiting the outcome and all along was agreeing with amp protection.   The fact you moved another amp and it is doing the same thing only adds another data point to support my theory.


First would be bad wiring or some other issue along that order.   I would split the output with a set of y cables, hook up the original amp to a test speaker with a short length of known good wire.  If the output in the mains goes away and you still have sound at the test rig you have now eliminated DSP and mixer.


The I would look in this order:  1 - Faulty speaker or wiring 2 - Issue with AC supply


Placing a UPS on an amplifier to correct a supply issue is not a correct option. That's just covering up the issue. 

[Mac Kerr]

First would be bad wiring or some other issue along that order.   I would split the output with a set of y cables, hook up the original amp to a test speaker with a short length of known good wire.  If the output in the mains goes away and you still have sound at the test rig you have now eliminated DSP and mixer.


The I would look in this order:  1 - Faulty speaker or wiring 2 - Issue with AC supply

Most of the time when a sound system is intermittent the problem turns out to be a cable.

Mac

[Mike Caldwell]

I had a service call at an install I did where they were loosing the high frequency ( tri-amped system). During walk in music it was kind of working, once the service started and the system was starting to hump a little the highs would start cutting in and out in an almost clock work like pattern. Someone had ran a drywall screw through the speaker line feeding the drivers on one side. Pulling the speaker lines off the amp and measuring the resistance of each found the problem line real quick, disconnecting it from the speaker proved it was somewhere in the speaker line real quick, checking the speaker cable from the amp out to the speakers not so quick.

Once your system starts muting does it go in and out of mute at some what regular intervals, that would be the amp over heating, cooling down, over heating, cooling down and again and again. That would also depend on how steady and hard the system is being driven.

[Billy Snody]

So did the meters on the DSP unit still show full active signal level?

Our DSP is a slave unit, 360-S, so I could not tell anything about indicators until I got logged into it after church. Sorry for delay. I have changed mixer outputs from M to L. I do seem to notice what I think is an overall reduction in output volume. All pans are centered. I have not been able yet to test in real session. Can anyone tell me if the green connectors on back of the Navigator unplug in case I decide to change some cables, which I am preparing for in the event that I still have this muting after the output change. Please correct me if I am wrong, but it seems to me that if the mixer is in mono, and the DSP has only the one input, should the volume not stay the same as the channels are summed? I'm not good yet at reading these block diagrams but it appears the L, R, and M all come from the same place. Maybe I am wrong, but I don't think it is a thermal protection issue. The second amp from the aux circuit, now on the FOH circuit, was not muting on the aux circuit. Is it possible that the "ribbon cable" for the L or R connect independently from the M? I am very intimidated about breaking open the mixer and getting it all reconnected properly. Thanks.

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