Keyboard Amp

bsr2002

bsr2002

Denny Crane
I have a Fender KXR200 keyboard amp. Been working well for 8 years now. Recently, when I turn the amp on it makes a shrilling noise, sounds like a smoke alarm only 10Xs louder.

Nothing is plugged into the amp, I just turn it on and it makes that noise. Maybe my horn driver is malfunctioning? Anyone had this experience before?
 
I don't know if the horn itself could do that, I've never heard of it.

One thing I've done for a long time because I always have had old stuff, plus I live in a highly corrosive environment, is:

Open up the unit. See if there are different pc boards connected by wires than plug in. If you can, carefully unplug all the plug in connectors, one at a time and spray a small amount of electronic cleaner (I personally insist on Deoxit D5 because it cleans and leaves an ideal film) on the contacts then plug the connector back in. Sometimes a Q tip works well to apply the cleaner.

How many times has a guitar crackled and all it is, is that the cable plug is slightly corroded? Same with telephones.

That's basically what I'm trying to rule out as being a cause. I have had lots of gear that that was all it was. I have a Harman Kardon amp that I need to do that to every couple of years.
 
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Someone on Facebook said it might be those two large transistors may need to be replaced.

But I also see a few plug in connectors and I will spray them. Where do I get DeoxIT D5...is it internat only or will Altex or Rat Shack carry it?
 
Rat-o-Shack sells some miniscule rip off size of Deoxit, I get mine from eBay from places like this: http://cgi.ebay.com/Hosa-Caig-DeoxI...651?pt=LH_DefaultDomain_0&hash=item4aa42ace4b

It doesn't have to be that brand. I got a brand from Home Depot once that actually melted plastic. :mad: so I always test unknown brands since that.

Here's another somewhat bozo thing that can reveal things: with the unit on and the top off, and it making the loud sound, take something that doesn't conduct electricity (like a pencil) and lightly tap components. Sometimes you can find a bad part that way if the sound changes when you tap it.

Also, really go over the pc board and carefully look at all the components. Look for any sign of thermal damage (fried-ness), or anything that looks abnormal.
 
Another thought: if the horn is a piezo (it won't have a crossover going to it, just come from one of the other speakers like a woofer) I'd try unplugging it in case that's the culprit like you originally asked.

If the tweeter comes from a crossover I'd want to substitute another same ohm value tweeter in it's place.

Maybe you were right, maybe it's the tweeter.
 
Looks like a horn to me, or is it piezo in a casing? I got some CRC Contact cleaner that I use in my car's electrical, should I try it first?
 

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It looks kinda like two piezo drivers mounted on a horn. I'm not certain though. Do they say anything on them, like 8Ω?

The wires that go to that horn, do they come right from the woofer speaker? If so they are piezos. What I'm getting at is that it would be nice to try the amp without the tweeter. If it's a piezo that's safe, if it's a horn that the amp needs to get a load say of 8Ω from then it would be bad to use the amp without the horn.
 
The red and black wires go from the board to the horns and the set of black and white wires go from the board to the woofer speaker.

The only thing it says on the horn is Motorolla and made in Mexico...lolz!
 
bsr2002 said:
The red and black wires go from the board to the horns and the set of black and white wires go from the board to the woofer speaker.

The only thing it says on the horn is Motorolla and made in Mexico...lolz!
Click to expand...

It sure sounds like a piezo to me, Motorolla made lots of them. The fact that it comes from the board bothers me though and would make me a little nervous running your amp without them. The fact that no Ω designation is present also seems like piezo-ness.

I'm not going to be the one that says to try your amp without the horn hooked up! I would hook a meter up to the horn and see what the resistance is and substitute a resistor in it's place just to be safe when testing the amp.

If anybody else wants to chime in on this it would be nice. I'm not sure if piezos have any resistance to speak of, whether they present, say a 8Ω load to the amp.

Do you have a multimeter?
 
dintymoore said:
It sure sounds like a piezo to me, Motorolla made lots of them. The fact that it comes from the board bothers me though and would make me a little nervous running your amp without them. The fact that no Ω designation is present also seems like piezo-ness.

I'm not going to be the one that says to try your amp without the horn hooked up! I would hook a meter up to the horn and see what the resistance is and substitute a resistor in it's place just to be safe when testing the amp.

If anybody else wants to chime in on this it would be nice. I'm not sure if piezos have any resistance to speak of, whether they present, say a 8Ω load to the amp.

Do you have a multimeter?
Click to expand...

I'm not getting anything, just 0
 
bsr2002 said:
I'm not getting anything, just 0
Click to expand...

The resistance of the horn is 0 Ω?

If that's the case then I would try the unit without the horn connected. Make sure the wires you unplug from the horn don't touch each other or anything else.

Maybe try one of the horn drivers disconnected at a time - it looked like there were two on it.
 
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