Behringer XY1200 Keyboard Amp repair?

[Enzo]

Maybe. The phones jack itself could be involved. The phones are driven off the main output. There is a resistor to limit power to the phones.

[valve king]

Hi there. You are just guessing and that doesn't make any sense. Use an oscilloscope and find your problem in minutes and be playing your amp instead of fixing it. I guaranty it.

[Enzo]

Hi valve king, welcome to the forum

As to guessing, that is not correct. If the original poster had a scope and knew how to use it, he wouldn;t be asking the questions he has posted. The suggestions we have offered are based upon specific experience with this model and the relative likelihood of where the problem might lie. We also make a point throughout this forum to stress troubleshooting techniques, many of which are simple and need no test equipment. We offered some tips on how to isolate the problem to specific areas of the system. As a rule I would not be looking for cracked solder on a speaker return with my scope. We also do not want him to make assumptions that might mislead him in the process, that is why doublechecking things like the crossover are important. AN intermittant in the crossover can cause trouble in the amp. I have the benefit of the schematic, as does John. The poster does not have that and has little chance of getting it. So I can suggest the TL074 on the jack board because I know from experience it will fail more often than other ICs in the preamp circuit. The poster would not know that.

[Steve Conner]

Well, if the crossover board had an open circuit, that wouldn't affect the headphone jack. But if it had something shorting out on it... Enzo said the headphone jack is dropped straight off the power amp output, so the headphone signal would be affected when the power amp got shorted out.

An intermittent short would also explain the smoke from your Crate keyboard amp.

[doc_drop]

All right. My post inspired some contraversy. Yeah!...

For my $.02 on the matter, it is true that I don't have a scope. I'm a pretty "skilled" hobbiest, but my experience is with stomp box clones and synths. So, I really, REALLY appreciate the common sense advice you guys with schematics and experience have given me.

I had assumed the issue with the Crate was that the x-over impedance was pulling more watts out of it than it was designed for. But if there is a possibility of a short, I will take another close look at the x-over. All I know is that if my solders looked as uniform, Hershey's Kiss-esque and shiny, I would be very impressed with myself.

Speaking of shorts. I mentioned in my previous post that I ran the cab with an approximately 1.5 amp 9v amp circuit called the Noisy Cricket. But I also bypassed the x-over and just hooked it up in series to the 8 ohm mid-range and out to the 4 ohm woofer. It worked great and got surprisingly loud. Is it possible the short is only happening at the higher amps of its amplifier? Would that cause something to arc/short that doesn't at lower amps and volume settings?

(Like I said, I appreciate you guys breaking it down for a hobbiest!)

[Steve Conner]

If you read again, I'm suggesting the short is in your crossover board. That explains why you didn't see it with the Noisy Cricket: because you bypassed the crossover. Not because it only happens at high power, though this may well be the case if it's triggered by vibration. And from your descriptions it does seem to be triggered by vibration.

Hence why I'm suggesting you repeat the experiment, but with the KX1200's own amp chassis wired directly to the woofer, instead of the Noisy Cricket thing.

[doc_drop]

Steve,

Hmm, I read again, but I don't see how this is talking about a short in the crossover:

so the headphone signal would be affected when the power amp got shorted out.

I guess you mean that a short in the x-over is part of/the same as a short in the power amp? Since the headphone out comes directly from the power amp out, per Enzo, I was thinking that would be before the x-over...

Anyway, I will do as you suggest and connect the Crate speaker out to the speakers bypassing the x-over, and while I have it open, I will reheat the solders. But, I sure hope I don't cause another arc in the Crate. I would hate to be out 2 amps!

Thanks for your help all the way from Scotland.

[Steve Conner]

That's not what I suggested doing either, though you can try it if you want.

I suggested that you take the Behringer amp chassis and hook it up to the Behringer woofer. You're basically putting the whole amp together again, with the crossover bypassed and only the woofer in use.

And yes, a short in the crossover could affect the signal from the power amp, even blow the power amp up.

[doc_drop]

Blow the power amp up!!! Uh, that isn't making me feel safe...

Anyway, sorry I misunderstood. That is a very good suggestion that I will try first. I never thought of doing that, even though it seems kind of obvious.

Sorry about the Scottish to "Amurican" translation difficulties.

[Enzo]

And to clarify my concern. If you plug in phones, then yes, the crossover and speakers are disconnected. But if a problem in the crossover had managed to damage the amplifier, then disconnecting it after that fact wouldn;t heal the amp. SO we want to make sure.

Plus the phones jack itself merits a check.

[doc_drop]

Sorry for not posting about this for a while. I got busy.

But check this out; before I even got around to plugging the amp back in, bypassing the x-over, I was fiddling around playing the noisy cricket through the cab. It was working fine, but all of a sudden it lost sound, kind of like the real amp was doing. I tried to find out what was wrong, when all of a sudden a cap in the cricket exploded!

Oh and while I am at it, my Crate has now stopped working. It did get damaged when I tried plugging its speaker out into the Behringer.

Does this give me any clues? Could it be that the same thing that caused my Crate to arc caused the cricket to blow up? If so, it must be something with the speakers themselves. The cricket mishap was while bypassing the xover, but the Crate wasn't.

The bottom line is that I now have 3 dead amps instead of one. (Of course I built the cricket so that is easy to fix.) I haven't even opened up the Crate yet.

Uh, anyone know a good repair palce in the SF Bay Area?

Thanks!

[ppouliot]

same problem with mine...

Loook's like the same problem. Sound become suddenly faint and scratchy. this will return to normal after 1 or 2 seconds most of the time. Once the problem was steady. I did some tests. the sound from each 4 entry and to the main out was verified ok. And the sound was bad from all tree speakers. I've been told it could be the crossover. sent it for repair. The guy found nothing worng but resolded a couple things. now after a couple month it's doing it again. Since it connot be thrusted, I had no choice but to order another amp last week. But I could still find some use for it if I can repair it. I know about nothing about electronics. But I visually inspected all components and checked all transfos with ohmmeter. (my multimeter can measure farad but I don't know how...) I'd like to try plugging in another amp and xover. Those components are small and seems very simples, I have the feeling it should not be so expensive? What should I use? I can also change every transfos but is it worth the time? One last thing; the problem can appear when the amp is completely cold or anytime.


Thank's
Pierre

[Enzo]

Try this - use a spare cord and plug it from send to return of the effects loop jacks

[ppouliot]

What is that loop back test supposed to check?
Now the amp is working fine again, do you tell me to check it the next time is goes wrong?

I plugged it as a bass speaker for the home cinema. I'll use it daily to diagnose as precisely as possible.

And by the way the fact that it is intermittant does that give you a clue?
At least some clue of what is not the problem...

[Enzo]

The FX loop external bypass connection is there to see if the FX loop jacks are involved. When you are NOT using them, little contacts in them carry the signal past. If those contacts get dirty or oxidized, then the signal gets lost. The bypass connection, well, bypasses that. If it restores the sound, the return jack needs service.

SOmetimes just probing a plug in and out of the FX return will trigger the symptom. Also if there is a power amp in jack, probe it with a plug.