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ElectroVoice CPS 4.5 series faulty protect circuit

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TPTech View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote TPTech Quote  Post ReplyReply Direct Link To This Post Topic: ElectroVoice CPS 4.5 series faulty protect circuit
    Posted: 29 March 2021 at 9:08am
Hi There!

Over the last week we had some weird glitch happen over the site that sent the amps into a weird pattern of popping noises/white noise out the speaker, and the amps constantly going in to protect mode.

After resetting the system, everything went back to behaving normally apart from 2 amps.

Even with no load and no input, the amp is still popping, going in to protect, rinse and repeat.

1x EV CPS 4.5 on channel 2
1x EV CPS 4.5 on channel 3+4

On the first amp, using the selector switch on the back, I put the channels in to bridge mode and both channel 1+2 started to go into protect. Swtiching it back stopped channel 1 going in to protect again.

When powered up, you can hear the relay on the protect circuit firing every few seconds.

I'm relativly new to the more detailed amp troubleshooting so I am wondering if any one here has some advice/experienced something similar? I have had a look around on this forum and I do have the schematic for the EV Q1212 series that was posted but obviously thats not the same amp! I have had a look through the manual from EV as well and it doesn't mention anything outside of the usual operation of the protect circuit.

Many thanks!




Edited by TPTech - 29 March 2021 at 9:09am
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studio45 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote studio45 Quote  Post ReplyReply Direct Link To This Post Posted: 05 May 2021 at 12:51pm
Sounds like you may have had a mains supply overvoltage event, if every amp at your site was affected. So I'd start by looking at what might be damaged by overvoltage in the amp...although that's almost every component! 

Most of the time, protection circuits operate when they have sensed DC at the amp outputs, this is usually caused by a shorted output MOSFET or transistor. This is also a common result of overvoltage events.
Try looking at the output of the faulty amps on a scope. A multimeter may not react fast enough to give you a reading on a DC fault before the relay clicks out again. The scope will show any brief spikes of voltage. Or, try metering the output line before the relay. If you see one of the DC rail voltages steady, it's a shorted output device for sure. 

Studio45 - Repairs & Building Commotion Soundsystem -Mobile PA
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simonp1100 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote simonp1100 Quote  Post ReplyReply Direct Link To This Post Posted: 05 May 2021 at 3:23pm
Sounds like a channel input op-amp fault to me. It could be either one of the channel balanced op-amps or the op-amp that does the bridge signal section. I think a circuit diagram would help you if you can get one.

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