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Old 30th March 2011, 11:35 PM   #1
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Default Help with Berhringer EP1500 :(

Hello everyone!

Im new to the world of pro audio and ive just picked up a set of cerwin vega cabs along with a free berhinger 1500 amp because it is 'faulty'. I am into electronic repair so thought that this may not to too hard to sort out saving me buying a 200 amp

The symptoms are as follows:

Once all hooked up i power the amp up (all gains set to 0 to avoid raping the cabs) and try to run some sound through it however the sound crackles like the audio quality is really poor. Also the whole time the clipping light is iluminated. The crackling starts at only 8db and gets worse any higher.

So far ive had the amp open to look for any outstanding problems such as blown/leaking caps and resistors. To my dissapointment i did not find anything apart from a few years dust build up which i hoovered up. Everything looks fine inside so ive no idea what could be wrong, ive also read up about faulty pots so i gave them a bit of a clean to get the gunk off from around them.

Still no luck... however before you ask about checking the cabs ive tested them with a cd player i had and they sound fine apart from a tweeter on one of the cabs appears to have stopped working. Could this have been a result from the amp being run in clipping from this fault?

If anyone can point me in the right direction it would be a real help.

Thanks
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Old 30th March 2011, 11:55 PM   #2
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Hi

check the op-amp's supply if its ok, usually a bad op amp if the clip led stays lit. This is a qsc rmx amp (clone ,spawn or whatever =)). The clip led is driven by the op-amp front end itself (the one that drives the driver stage and the op stage).
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Old 31st March 2011, 04:32 PM   #3
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Thanks for the quick reply but like i said im pretty new to amp internals so im not sure what im looking for. The psu looks fine to me but i can post some pictures and maybe a video for you to watch the syptoms first hand.
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Old 31st March 2011, 07:02 PM   #4
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Is it doing it on both channels?
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Old 31st March 2011, 10:52 PM   #5
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Here you go, IC2a - IC2b and IC4a - IC4b (SMD) (please refer to the schematics attached) were the parts I am referring to.
Attached Files
File Type: zip behringer-ep1500-pwr-sch.zip (159.6 KB, 125 views)
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Old 1st April 2011, 02:05 AM   #6
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Yes kev, it does it exactly the same on both channels which makes me think something is up with the psu like it has been mentioned. I don't have time at the moment to look but ill update with pictures when i do. Cheers again lads
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Old 4th April 2011, 04:15 PM   #7
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Hello again, tried to find the components that you were refering to but i cant seem to find them on the board in the amp itself. Ive got some pictures of the amp and a video outlining the problems. Can you point me in the right direction of where and what i should be looking for (blown caps, burnt out traces?).

Also would a poke around with a multimeter help? If so what settings should i have it at?

Pictures below, video can be found here: YouTube - Behringer EP1500 Fault!

Click the image to open in full size.

Click the image to open in full size.

Cheers.
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Old 4th April 2011, 08:40 PM   #8
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Forgot to mention on the last post but in the video i only use one channel however the exact same thing happens on both channels.
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Old 5th April 2011, 09:07 AM   #9
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Anyone got any ideas? Someone must know, you lot seem like you know everything to do with amps.
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Old 5th April 2011, 09:55 PM   #10
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The parts mentioned in the other post by 'Audiomachines' are mounted on the other side of the board. You will have to take it out.

Also check the mains switch. They can arc under slight load which will show as crick-cracking through the audio. A quick check is to short it out with a wire link.

Another thing to affect both channels is the wiring loom going from the main board to the input board on the back and the volume board on the front. Behringer use cheap connectors and sometimes they dont mate properly. Wiggling them carefully while the amp is showing the symptoms will prove if this is a problem.

Try checking the two bridge rectifiers, they are wire-ended and sometimes the leadout wires actually develop hairline cracks and pull out of the moulded bridge under the weight of the pcb.

Dont forget that any arcing no matter how small on one channel can conduct interference through to the other so it makes both channels look faulty.

Last edited by kevvywevvywoo; 5th April 2011 at 10:00 PM.
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