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Author Topic: Clip light on Crown amps  (Read 7097 times)

Joseph D. Macry

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Clip light on Crown amps
« on: September 02, 2016, 04:50:20 pm »

I'm servicing sound system at a high school football field. There are several Crown CTs2000 amplifiers all receiving the same signal from DSP.
Two of these amps show one red clip light (it comes and goes) even though audio is below clipping. All speakers are producing audio.
The signal meters on the channel with clip light runs a little lower than the other side, even in parallel (Y-input) mode.
What could the red clip light be telling me, if not clipping nor protect mode?
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Joseph Macry,
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Lee Buckalew

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Re: Clip light on Crown amps
« Reply #1 on: September 02, 2016, 04:54:46 pm »

I'm servicing sound system at a high school football field. There are several Crown CTs2000 amplifiers all receiving the same signal from DSP.
Two of these amps show one red clip light (it comes and goes) even though audio is below clipping. All speakers are producing audio.
The signal meters on the channel with clip light runs a little lower than the other side, even in parallel (Y-input) mode.
What could the red clip light be telling me, if not clipping nor protect mode?

One of the more common problems indicated by the clip lights acting as you are describing is failed portions of the output stage.  That is where I have typically seen this.  If that is the cause it will require replacement of internal parts.

Lee
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John Roberts {JR}

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Re: Clip light on Crown amps
« Reply #2 on: September 02, 2016, 04:59:05 pm »

I'm servicing sound system at a high school football field. There are several Crown CTs2000 amplifiers all receiving the same signal from DSP.
Two of these amps show one red clip light (it comes and goes) even though audio is below clipping. All speakers are producing audio.
Quote from: from OM
a. Fault indicator
Red LED, one per channel,  ashes when the ampli er output channel has stopped operating. Usually this means that the ampli er must be serviced.

B. Thermal indicator
Red LED, one per channel, illuminates when the channel has shut down, or is very near shutting down, due to thermal stress or overload.
The signal meters on the channel with clip light runs a little lower than the other side, even in parallel (Y-input) mode.
What could the red clip light be telling me, if not clipping nor protect mode?
http://rdn.harmanpro.com/product_documents/documents/1945_1407779508/141280-1_CTs_2ch_series_operation-08-13_original.pdf

When in doubt RTFM

JR
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Lee Buckalew

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Re: Clip light on Crown amps
« Reply #3 on: September 02, 2016, 05:05:33 pm »

The signal meters on the channel with clip light runs a little lower than the other side, even in parallel (Y-input) mode.
What could the red clip light be telling me, if not clipping nor protect mode?

http://rdn.harmanpro.com/product_documents/documents/1945_1407779508/141280-1_CTs_2ch_series_operation-08-13_original.pdf

When in doubt RTFM

JR

Those are all true John, I have also seen the clip indicators light with damaged output sections.  I have seen this repeatedly, on different CTs on the same install. 
CTs were quite awful when they first came out, lots of failures.  This was fixed in the 4 and 8 channel models and the later 2 channels.  Don't know that the stigma of the early problems ever wore off.

Lee
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Joseph D. Macry

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Re: Clip light on Crown amps
« Reply #4 on: September 02, 2016, 05:06:22 pm »

Here is a pic
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Joseph Macry,
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Joseph D. Macry

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Re: Clip light on Crown amps
« Reply #5 on: September 02, 2016, 05:10:25 pm »


a. The channel has not shut down. Speakers are producing audio.
b. I don't suspect thermal stress, as this light is usually on as soon as the amp is turned on.

A rep from Crown tech support suggests the following: "If a clip light is on, with or without audio and the audio is fine, my guess is the 50 pin cable is acting up. Could be a reference point being lost due to the cable causing the led to turn on. If the front end board was bad, which can cause the clip led to turn on, no audio would pass."
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Joseph Macry,
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Scott Carneval

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Re: Clip light on Crown amps
« Reply #6 on: September 02, 2016, 05:14:21 pm »

Older MacroTech's had an IOC (Input Output Comparator) circuit that would light to indicate the output varied by more than .05% from the input. Maybe these CTS series clip lights were based on a similar circuit.


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John Roberts {JR}

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Re: Clip light on Crown amps
« Reply #7 on: September 02, 2016, 05:35:11 pm »

Older MacroTech's had an IOC (Input Output Comparator) circuit that would light to indicate the output varied by more than .05% from the input. Maybe these CTS series clip lights were based on a similar circuit.


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I was going to suggest something like this, in fact many clip limiters are built on a similar detection topology.

When comparing real output, to a virtual what output should be, any number of faults that prevent output from hitting full target levels will indicate fault. For example current limiting or weak output stage devices would indicate pretty similar.

JR
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Joseph D. Macry

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Re: Clip light on Crown amps
« Reply #8 on: September 06, 2016, 04:48:09 pm »

Older MacroTech's had an IOC (Input Output Comparator) circuit that would light to indicate the output varied by more than .05% from the input. Maybe these CTS series clip lights were based on a similar circuit.


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Would such an IOC circuit light up before audio input is turned up?
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Joseph Macry,
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John Roberts {JR}

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Re: Clip light on Crown amps
« Reply #9 on: September 06, 2016, 05:05:06 pm »

Would such an IOC circuit light up before audio input is turned up?
It could... Suppose the amp output is supposed to be 0V and it isn't. The input-output-comparator, compares what it should be to what it is and says no match so lights up.

Crown service should be the experts about what you are dealing with, not me.

JR
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Mike Diack

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Re: Clip light on Crown amps
« Reply #10 on: September 18, 2016, 03:41:17 pm »

Re spurious clip lights on CTS2k & 3k, there are a few "usual suspects".
1: The 50 way ribbon cable between the input board and the main board - can be verified by wiggling the cable while running signal through the amp and observing what happend.
2: Loose faston connectors on the "tails" from the Lp/Ln chokes. Easily fixed by removing, squishing with pliers, and reconnecting.
3: There is a _|----------|_ shaped bracket under the output filter board tying the grounds together and contacting the case. The old version has a conductive squishy foam doing the case contact, the new version has sharks teeth. Fit the new version. While you're there, verify the tightness of the 8 screws that tie the main board to the output filter board.
4: It could be slightly blown up.
M
« Last Edit: September 18, 2016, 03:47:26 pm by Mike Diack »
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Re: Clip light on Crown amps
« Reply #10 on: September 18, 2016, 03:41:17 pm »


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