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Desafinado 5th March 2012 07:12 PM

Kicker Kx 500.2 Amp.
Hi to everyone. My name is Luis, from mexico.

I have been installing car audio equipment for some years, but really i have never messed up with electronics very much. Yesterday a friend of mine brought to me a Kicker KX 500.2 . He said his brother removed form a previous installation, but no problems were reported to him. He tried to install in his own car but have no luck. He told me the amp had no audio, and told me how he connected it and was correct (he connected to a pair of working 6x9 speakers), even he installed its previous amp and worked well in that configuration.

Here is what is happening.

1.- I tryed to power up the amplifier, feeding with 12.10 volts from a power supply, feeding signal from a good known RCA wires, and feeding audio signal from my own PC. The amplifier red led lits at start, and 3 seconds or so, it changes to green, but no audio cant be heard.....well, if you pay attention very close, you actually can hear what music is playing, but very, very faintly with noise.

2.- Even with this, if you move the gain (or the volume in the PC) the signal get a little bit louder, but not very much. You can feel the cone of the speaker (tested with a 6" 4 ohm driver) moving.

3.- Checked the fuses, (two 35 Amp) with the dmm, they are in correct working order.

4.- Openned the amp, and inspected the board visually. No blown components at sight, smoke or odor.

5.- Checked the "preamp board" (sorry if its not the correct name, its the removable board wiht pins and RCA inputs), no evident signs of damage. Removed and reseated but no change. It has the same behavior.

6.- Removed PCB from heatsink, and no burned traces (there are minor exceptions when i was able to repair an amplifier fixing these....).

Aditionally, if you let the amp playing with the very vey low volume for some time, the transistors get a little warm. Not very much, but you can feel it.

I`m not very good at this, but i can use a multimeter and have basic knowledge in cars. Would be great to know what i can do for this device. If you need any pics just ask.

I apologize for my english im still not very good. Any help would be very appreciated.

Greetings from Puerto Vallarta.

Perry Babin 5th March 2012 07:27 PM

On the preamp board, with the black probe on the GND pin, do you read plus/minus 15v on the pins marked +15 and -15?

Desafinado 5th March 2012 08:31 PM

Hi Perry Babin, thanks in advance:

Tested the pins in the preamp board:

black probe in GND and +15 = 15.14 V

black probe in GND and -15 = 7.0 V.

Perry Babin 6th March 2012 12:14 AM

Post a photo of the board in the amp.

One of the regulators is defective. It will need to be repaired but you should modify the regulators a bit to make them more reliable. More on that later.

Desafinado 6th March 2012 06:45 PM

1 Attachment(s)
Hello again.

I took the picture of the preamp board as requested, i hope it will work.Im not really good taking photos.

Let me tell you something strange. The main board of the amplifier was very dusty, so i decided to clean it with a soft cloth with little wd-40 to get a better picture of it. I decided to take another reading of the values GND to +15/-15V and got:

Black probe GND/+15V = 14.72

Black probe GND/-15V = -12.82

That looked strange to me, but i decided to give a shot. I set up two 6x8 8 ohm speaker in each channel and played some music, and the amp worked as normal. No strange noises, gain was responsive, x overs vere working,both channels played clean and smoothly, etc, after the amplifier went from red to green led.

Obviously i dont believe that the amplifier "repaired itself", and when i had like a minute or so with the amplifier playing, i feeled that to transistors (The ones indicated with the yellow lines, Q15 and Q16) started to feel real hot, so i turned off the amp. I waited a little, and turned the amp on again, and the amp worked normal, but these two parts still were getting hot, in like a minute or so. So i hope that this information i got will help. Thank you very much.

Q15 is labeled 2SD669
Q16 is labeled

So i hope that this information i got will help. Thank you very much.

Perry Babin 6th March 2012 08:20 PM

1 Attachment(s)
They often fail because they operate at such high temperatures. The intermittent -15v is likely caused by oxidation of the solder connections for the B649. The attached shows one solution that holds up well. The transistors are 2N6488 and 2N6491 (B649).

Desafinado 6th March 2012 08:29 PM

Thanks for the quick response !

So should i need to check and resolder both components or they need replacement?

If i can still use them, can i make a custom heatsink or its not an acceptable solution? i have some CPU heatsinks laying around so i think i can cut one of these to fit , according to your photo.

I greatly appreciate your help. Thank you again.

Perry Babin 6th March 2012 08:37 PM

If you are going to re-use those transistors, add new solder, desolder them and resolder them. You must get rid of the old solder.

You can use a different type of heatsink but it must not have its weight supported by the transistors unless it's very lightweight.

If the backs of the transistors have an exposed metal area, you need to use an insulator between the sink and the transistor unless you can be absolutely sure that the heatsink cannot come in contact with anything else (not even the other heatsink).

Desafinado 7th March 2012 07:10 AM

I removed both transistors, cleaned the traces of the old solder, reinstalled and applied new solder. The amp still works normal but i think the transistors get hot very fast. 30 seconds more and they are hot, i even tryed them with a small piece of copper working as heatsink, but two minutes were enough to be very hot to heat the copper heatsink. So, what would be best? should i need to get the same replacements or there are better ones...if so, which are they ?

Or i need to continue trobleshooting the board to check what is happening to get these transistors hot.

Thanks in advance.

Perry Babin 7th March 2012 01:07 PM

2 Attachment(s)
Regulator transistors get hot. That's normal. If you have a capacitor that's leaking (electrically) on the output of the regulator or have a defective op-amp, that could make them heat up more than normal but those problems are relatively rare.

In some amps, I move the regulator transistors to allow them to contact the heatsink. In the first image there is a piece of closed cell foam between the transistor and the board. This keeps the transistor tightly against the heatsink. If you do anything like this, you must make sure that the transistor is insulated from the heatsink.

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