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sub amp keeps blowing


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mmcelroy 
Member - Posts: 6
Member spacespace
Joined: January 15, 2008
Location: Georgia, United States
Posted: January 15, 2008 at 9:28 AM / IP Logged  

I've had my Kenwood KAC-728s amp in my car for almost 7 years now and not long ago it stopped working.  I have replaced all of the power cables that lead up to it and tested them with a voltage meter to make sure everything seems in place but for some reason the fuses on the amp keep blowing. 

I disconnected the speakers and the fuses still blow.  I took the amp apart and nothing looked fried or shorted.

I'm trying to narrow down what the possible problems could be.  Is it likely that my amp is fried?  Is it possible somehow that there is a short somewhere else in the vehicle that could cause this problem (I'm certain that the actual wires leading to the amp are in tact)?  Any other ideas on what could cause this?

I am hoping to test the amp in a friends car to see if that works, but until then I am clueless.

haemphyst 
Platinum - Posts: 5,054
Platinum spaceThis member has been recognized as an authority in Electrical Theory. Click here for more info.spaceThis member has been recognized as an authority in Mobile Audio and Video. Click here for more info.spacespace
Joined: January 19, 2003
Location: Michigan, Bouvet Island
Posted: January 15, 2008 at 10:00 AM / IP Logged  
If you are blowing fuses with no load attached at all, the amp is toasted. Bad news, but that's the fact...
It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."
Alpine Guy 
Platinum - Posts: 2,478
Platinum spaceThis member has made a donation to the12volt.com. Click here for more info.spacespace
Joined: October 18, 2003
Location: Canada
Posted: January 15, 2008 at 10:48 AM / IP Logged  
Sounds like the power supply has a short, you could have it repaired locally, but to pay a professional to do it would almost equal to the cost of a replacement amp.
If your willing to learn how to repair it you can get your hands on a repair dvd from here http://www.bcae1.com/repairbasicsforbcae1/repairbasics.htm .
I picked it up and have been able to offset the cost of it by doing a few repairs now.
2003 Chevy Avalanche,Eclipse CD7000,Morel Elate 5,Adire Extremis,Alpine PDX-4.150, 15" TC-3000, 2 Alpine PDX-1.1000, 470Amp HO Alt.
mmcelroy 
Member - Posts: 6
Member spacespace
Joined: January 15, 2008
Location: Georgia, United States
Posted: January 15, 2008 at 11:40 AM / IP Logged  

When you say that the power supply has a short, I guess I don't follow... and this is where the bulk of my confuision comes from.  If my amp is blown, that's easy to comprehend, I get that.  The issues with the power supply is a bit of a mystery to me and perhaps someone can explain better.... 

Things I know:

1) I am certain that there are 12 volts coming from the battery.  I am also certain that the (6 or 8 gauge, can't remember) wire coming from the battery is in tact and is not shorting out anywhere.

2) I am certain that the remote power (I think that's what its called, from the head unit) is at 12 volts and I re-ran that wire as well.  Can't say as confidently that there isn't a short, but likely not.

Things I don't know:

1) If somehow there was a short in the car, I would assume that it would have to be outside of the positive leads that are connected to the amp because of the things that I know listed above.  Thus can a short in another part of the car (ie, dashlights, powerlocks, alarm, etc) cause the ground to the amp to create a power supply problem AND not affect any of the other electronics in the car?

2) Is there a way to test the amperes to the amp to see if they are too high?  (I would think not and this is where my electrical expertise begins to dither, but the fuse on the power cable (60amps) does not blow)

advanced_audio 
Copper - Posts: 170
Copper spacespace
Joined: July 07, 2006
Location: United States
Posted: January 15, 2008 at 11:50 AM / IP Logged  
The amp is toast. Buy a new amp or have it repaired.
mmcelroy 
Member - Posts: 6
Member spacespace
Joined: January 15, 2008
Location: Georgia, United States
Posted: January 15, 2008 at 12:12 PM / IP Logged  

Alpine Guy thanks for the link... just checked out the site and it looks like it is the output transitors.  I may see if I can fix myself, if not I'll get a new amp.

Thanks

Alpine Guy 
Platinum - Posts: 2,478
Platinum spaceThis member has made a donation to the12volt.com. Click here for more info.spacespace
Joined: October 18, 2003
Location: Canada
Posted: January 15, 2008 at 10:05 PM / IP Logged  
Yup, by meaning a short in the power supply , I meant the power supply inside the amplifier. It can be very easy to fix with the help of the amplifier dvd I linked you to.
2003 Chevy Avalanche,Eclipse CD7000,Morel Elate 5,Adire Extremis,Alpine PDX-4.150, 15" TC-3000, 2 Alpine PDX-1.1000, 470Amp HO Alt.
i am an idiot 
Platinum - Posts: 13,666
Platinum spaceThis member consistently provides reliable informationspace
Joined: September 21, 2006
Location: Louisiana, United States
Posted: January 16, 2008 at 3:53 PM / IP Logged  

This is an easy amp to repair.  You should be able to fix it for under 40 dollars.  If you are interested and need a little help just let me know.

mmcelroy 
Member - Posts: 6
Member spacespace
Joined: January 15, 2008
Location: Georgia, United States
Posted: January 20, 2008 at 12:17 AM / IP Logged  
So I tested the output transistors in the amp and noticed that one of them was shorting out between two of the leads.  I bought a replacement transistor and after putting everything back together I put the amp in my car and BINGO! it worked! .... for about 15 mins :(.  I took the amp back apart and now 2 of the 4 output transistors are shorting, 1 of which is the one I just replaced.  Can anyone help me figure out why this is happening?  Could it be that the gain is turned up too high on the amp?  Could it be that the sub is drawing too much power from the amp?  Is there something else going on in the amp that needs to be fixed?  I am hesistant to just go buy more transistors if this is going to keep happening.
mmcelroy 
Member - Posts: 6
Member spacespace
Joined: January 15, 2008
Location: Georgia, United States
Posted: January 20, 2008 at 12:34 AM / IP Logged  
Thinking out loud here but I just realized that the specs on the amp are 600w @ 4 ohms (bridged) and the sub is rated for 150-225w @ 4 ohms... would having an amp that is too powerful hurt the amp?  If I put the amp in stereo mode then it is rate at 200w which is line with the sub, should I replace the transistors and then leave it in stereo mode?
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