Behringer XY1200 Keyboard Amp repair?

[doc_drop]

Hey guys.

I'm hoping someone can help me decide what to do about this stupid amp I bought. I wanted to use it as my 2-person-band's PA. It worked great for about a year. But after 4 or 5 gigs, it crapped out on us mid-set. I have done many searches trying to find service info. and/or schematics of the amp circuit, but it turns out Behringer keeps it secret.

Has anyone ever repaired one of these? If so, what should I look for? I have heard the LM3889 chip is often the problem. I also heard replacing the electrolatic caps helps. But, I don't want to do too much work if the thing is just going to crap out during a gig again.

Any ideas?

[Enzo]

I don't see XY1200, but assuming it is similar to KX1200...

Plug a signal into the power amp in jack. ANy sound? If not, check the speaker, does the speaker itself make sound? Touch a 9v battery to its terminals for a moment, a good speaker will pop. Pull the wires off first. If speaker is OK and no sound, then check internal power supply. If that is OK< then I would indeed suspect the power amp IC.

Play into the front of the amp. ANything coming out the preamp out jack? COnnect that to some other amp for a listen.

Got effects send and return jacks? Try plugging a signal into the return and listen out your speaker. Likewise send the FX send signal to some other amp for a listen.

All these things are to isolate the problem to a section of the amp.

In my experience, the most common repairs have been the TL074 IC on the jack board, voltage regulators on the power amp for +/-15v. And th occasional power amp IC.

[doc_drop]

Thanks Enzo. That is a very rational sounding system to isolate the problem. It is KX1200, BTW. Sorry about the typo.

Did I read that are an authorized repair person for Behringer? I have read some bad things about this amp online. Do you think it is worth fixing it? I can't have a PA amp that craps out during sets.

I am thinking that if I can't fix it reliably, I am going to try using it as a speaker box only...

[Enzo]

If I were outfitting for the road, I personally would be looking at Peavey. I have no gripe with the Behringer gear other than I think it is a bit lightweight - as in I wouldn;t toss it around and expect it to hold up. Worth fixing? To me, of course it is.

This is a popular model. SO I have seen a few. Any popular product will be in my shop more than ones that don;t sell.

Until we know what is actually wrong with your amp, it is hard to comment on the implications to reliability.

[doc_drop]

Fair enough, Enzo. I'll take a poke at the guts with my DMM and report my findings. It may be a few days before I post again, but I will let you know.

Thanks for the info. in any case. You've been a great help.

I think Behringer is making a huge mistake not letting people see the schematic, though... I won't buy another of their products just because of that.

[Enzo]

Many companies consider their schematics proprietary. CAll Line 6 and ask for a drawing. Call Nady and ask for a drawing. I always found it ironic that on my Fender schematics there is a note claiming the schematic is proprietary and not to be shared without written permission from Fender, yet they throw a copy inside their amps with the instruction manual when they ship them. I have signed non-disclosure agreements with a number of factories as part of my service center status.


The VAAAAAASSSSSST majority of people buying an amplifier would have zero idea what the schematic meant, and in other cases would invite attempts to work on it by people more likely to cause more problems. Only a tiny minority of people could actually make use of a schematic - for anything, not just Behringer - so while it might irritate you, it is a non-issue sales wise. If someone's amp breaks and they try to fix it and it blows up further, they won;t be thinking they were not up to the repair, they will be thinking "damned Behringer stuff blows up and you can;t fix them." Or Fender, or Peavey, or whoever.

[jrfrond]

The KX1200 is actually a fairly-reliable amp. You MIGHT have an amp problem, then again, you might not. I've seen soldering issues with the passive crossover in the speaker cabinet too.

Before you go poking around in there, let me caution you that Behringer employs fairly dense surface-mount PCB topology in their gear, and the KX1200 is no exception. There is no component location silk-screening on the PCB's, and without a schematic, you will just be guessing (and even WITH one, it's a bit tedious). You can get your hands on an LM3886 and swap it (let me caution you again about the double-sided PCB's), but beyond that, you are going to be pissing in the wind.

[Enzo]

Oh, I had completely forgotten about the sad little crossover on the rear wall of the cab. Yes, those tend to shake themselves apart. That would be a great thing to check first.

Try the headphones jack, if it works, then the amp chips are working. The phones are dropped right off the speaker line.

[doc_drop]

Enzo and jrfrond.

Lot's of info.! Not all of it encouraging. But I am going to give finding out what is wrong a shot. I don't have much to lose. I'll post once I have results. Probably after the weekend.

I see what you mean about schematics. Too bad there aren't any "unauthorized" versions floating around, that Behringer doesn't have to assume any liability for.

Anyway, of course I am a little unhappy with the monster, but of course all companies have to deal with production issues, etc. That is why making your own gear is so empowering. (I only make effects boxes....so far.)

[Enzo]

After John's mention, I would really suggest pulling the speaker and checking that crossover in the enclosure.

[doc_drop]

Yeah Enzo. That is the first thing I will check. It would be awesome if it was something so simple.

I'll post after the weekend to let you guys know how it went.

[doc_drop]

O.K. Just reporting in on the "progress" I made last weekend.

I first looked at the crossover in the rear of the cabinet. It was absolutely clean as a whistle. Beautiful solders with no damage at all.

So, I decided to try to isolate the problem. I first plugged my stereo signal into in 1 & 2. It works fine for a while at low volumes. But when I pump up the volume it starts to crackle and sometimes loses volume all of a sudden by at least 6db. I tried all the channels, with headphones and through the cab. It does the same thing for all channels.

So, I decided to try using either the tape ins and the FX return to input the signal. It works a little better, in that I can push the volume a little harder. But at a certain point (and I'm talking at about 45% on the volume knob) crackles and loss of volume.

I figured it must be a problem with the amp circuit. But when I looked, even though I see the 2 LM3886's etc., but it is all SMT, and it looks like it was built by a robot with a human applying gobs of hot glue after. I just don't feel comfortable trying to replace parts in this kind of computerized technology.

So, on to phase 2, aka what can I use this useless box for. I unplugged the wires running to the crossover. I tried plugging a chord out of my little Crate keyboard amp speaker out, and connecting it to the crossover. It sounded like crap, and I heard something arc and start to make our favorite, I just burned some electronics smell. Luckily after a quick power off that amp is fine.

I next decided to use the Noisy Cricket I just built to power the thing. I pulled the speaker cable off the crossover, and started connecting the speakers to the amp. The 8 ohm mid range sounded pretty good. But it sounded best if I ran the mid range and the 4 ohm woofer in series. I don't know why in terms on impedance, and I hope I won't burn out my Cricket, but it works pretty well. And it gets pretty loud.

So, I have a temporary use for the cab of the amp at least.

But, does anyone know of a kit or project to build a mono amp that could handle this speaker box? Any ideas on how to go about figuring out what amp would work best?

Thanks for all the suggestions!

Doc DROP

[Enzo]

Did you connect the KX amp chassis to a different speaker cab? You really owe it to the amp to verify the amp chassis has the problem or not. otherwise you might be replacing a perfectly good circuit.

[Steve Conner]

It really does sound like the crossover board has a loose contact or an intermittent short. Sometimes you get a "dry joint" - a solder joint that looks normal but actually isn't making any connection.

Try losing the crossover and hooking the output from the KX amp straight up to the woofer.

[doc_drop]

Steve and Enzo,

Thanks for the ideas.

I'm not sure I understand. Doesn't listening through the headphones out eliminate the cab and crossover from the equation? Is the crossover accessed when listening on headphones?

If I had a schematic (or at least a block diagram) I would know this!