Help with Berhringer EP1500 :(

Phreaktwo

Member
2011-03-31 12:06 am
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 :)
 

Phreaktwo

Member
2011-03-31 12:06 am
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!

[IMGDEAD]http://img690.imageshack.us/img690/8485/img20110404161502.jpg[/IMGDEAD]

[IMGDEAD]http://img819.imageshack.us/img819/2558/img20110404161534.jpg[/IMGDEAD]

Cheers.
 
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.
 
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Phreaktwo

Member
2011-03-31 12:06 am
Thanks for the reply kev, i'll be sure to have a good look around for any faulty connections that may lead to arcing. Ive taken some pictures below of the op amps and a certain solder joint that looks a bit suspect. Tell me what you think but to me there doesnt seem to be any problem with the op amp...

[IMGDEAD]http://img39.imageshack.us/img39/5803/img20110405124654.jpg[/IMGDEAD]

[IMGDEAD]http://img140.imageshack.us/img140/6398/img20110405124813.jpg[/IMGDEAD]

[IMGDEAD]http://img638.imageshack.us/img638/5619/img20110405124820.jpg[/IMGDEAD]

[IMGDEAD]http://img218.imageshack.us/img218/3231/img20110405130342.jpg[/IMGDEAD]

[IMGDEAD]http://img52.imageshack.us/img52/8141/img20110405130401.jpg[/IMGDEAD]


[IMGDEAD]http://img853.imageshack.us/img853/6248/img20110405130448.jpg[/IMGDEAD]

[IMGDEAD]http://img854.imageshack.us/img854/6639/img20110405130805.jpg[/IMGDEAD]
 

Phreaktwo

Member
2011-03-31 12:06 am
Ah right, i wasnt aware that they dont change when faulty, where would i be able to pick up new ones from? What do you think to the look of the transistor? The pcb underneath it looks pretty fried, could this have failed? I also had a good poke around for arcing and everything seems fine.

'Input stage fault, take schematic!' What do you mean by this zeonrider?
 
Don't replace the op amp if you hadn't perform these test yet, Set the level controls at full kill, try and measure the VCC+/- of the op-amps, There should be a 15+/- on the supply pin reference to chassis ground ("ground" on this type of amp topology is a bit misnomer). If missing please refer to page 3 of the schematic (the power supply section).