Kicker Kx 500.2 Amp.

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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.
 
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
2SB649

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

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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.
 
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).
 
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.
 
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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some progress...

Thanks again!

Here is some progress.

I decided to put both transistors in the heatsink of the amplifier. I have some sil-pads laying around, so i drilled a bit and they are ready to install. I have checked again the amp before assembling and i noticed that the blue resistor besides B649 gets very warm to the touch, in like 20 seconds is enough hot so i checked i made a bad solder conection or bridged something. Needless to say, the amp works as before, im just not trust about that part getting hot. I will have to ask, is this normal too? im afraid to burn something else.

I greatly appreciate your help.
 

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Im back with the readings:

Voltage across ZD4 and ZD5 is nearly equal

ZD4 15.39

ZD5 15.34

Resistor Values=

R45 = 3240 OHM

R46 = 323 OHM

R47 = 323 OHM

R48 = 3020 OHM


R47 gets hot really fast. I checked my psu and got 11.02 volts, so "just in case" i changed for another PSU, which gets 12.30 with the amp running, and the only change was getting hotter more fast R47. I´m going to recheck my soldering points of the wires of the regulators to see if one is bridging. Thanks.
 
Thank You.

Voltage readings from R46-R47 with the amp powered up, preamp board installed:

R46=17.22
R47=25.5

Without preamp board, the values change very much:

R46=8.6
R47=15.8


I´m going to search the internet to check how to test properly a cap, since rarely i test one, and im going to be back with the readings of C221. It is a 4.7 milifarad 50V, or at least its what it reads.

Thank you very much.
 
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I think will be better to go grab some capacitors from the electronics store. I have a question:

While im there, it will be better to get some other parts that might be replaced too? if so, which ones? some resistors, diodes, some upgraded part? so i can get everything i need from my trip.

And the other question it is if i need to get the exact replacement of the caps? (4.7 milifarad 50V). Currently, there are five at the store:

Capacitor electrolítico chico, no polarizado, radial, de 4.7 uF (micro Faradios) a 50 Volts

Capacitor electrolítico radial, de 4.7 uF (micro Faradios) a 100 Volts

Capacitor electrolítico radial, de 4.7 uF (micro Faradios) a 160 Volts

Capacitor electrolítico radial, de 4.7 uF (micro Faradios) a 350 Volts

Capacitor electrolítico radial, de 4.7 uF (micro Faradios) a 63 Volts


Hiperlink:

Capacitores electrolíticos 4,7 uF en Steren

Thanks in advance.
 
Hello again.

Went and brought from the store a pair of 4.7 microfarad 63V caps (there werent 50v ones). I removed both C121 and C221 and tested. R47 is still getting very hot. R46 is normal. Audio quality is not affected.

Q16 and Q15 are not getting hot, that`s good news. (Maybe they got hot because they were initially near of R47)

Like you said, maybe R47 resistor should be hot with normal operation. I have plans of assembling it and tested a day or two, but im affraid of blowing something because the high temp of R47.

Thanks in advance, i keep you posted.
 
R46 = 17.08
R47 = 16.50

Well, i started to think im bothering a lot with this amplifier, so i assembled it an played for a few minutes, 10. Both R46-R47 gets very hot.

Plays beatufully, everything working.

I talked with my friend about this, and he said to me that his brother (he was told the real story...) when was using the amp, he plugged a speaker wire to the outpots of the amp TO ANOTHER WORKING AMP, accidentally (a USAMPS xt2000d), instead to a subwoofer (because he was thinking that wire was routed to a speaker...) much like like "amplifier chaining" .

The amp didnt stopped working that day. One month or so after that incident, they were using the 500.2 with 4 6x9 speakers at low volume, playing for like an hour, the amp sounded what he described to "very much pink noise" (i think a wire of a speaker got grounded to the car chasis)
and stopped working. They removed the amp, tested in another car but played fine. They decided to remove from the car it was, and sat like 2 or 3 years, when finally the amp fall into my hands.

Maybe im being too ambitious trying to repair this amp (because i can have it if i can repair it...) without the proper knowledge. I am going to give another shot to the board if i can detect something.

I truly appreciate your valuable help Mr. Babin. Thank you.
 
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