sub amp keeps blowing
Printed From: the12volt.com
Forum Name: Car Audio
Forum Discription: Car Stereos, Amplifiers, Crossovers, Processors, Speakers, Subwoofers, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=101182
Printed Date: April 29, 2024 at 10:31 AM
Topic: sub amp keeps blowing
Posted By: mmcelroy
Subject: sub amp keeps blowing
Date Posted: January 15, 2008 at 9:28 AM
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.
Replies:
Posted By: haemphyst
Date Posted: January 15, 2008 at 10:00 AM
If you are blowing fuses with no load attached at all, the amp is toasted. Bad news, but that's the fact...
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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."
Posted By: Alpine Guy
Date Posted: January 15, 2008 at 10:48 AM
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 https://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.
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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.
Posted By: mmcelroy
Date Posted: January 15, 2008 at 11:40 AM
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)
Posted By: advanced_audio
Date Posted: January 15, 2008 at 11:50 AM
The amp is toast. Buy a new amp or have it repaired.
Posted By: mmcelroy
Date Posted: January 15, 2008 at 12:12 PM
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
Posted By: Alpine Guy
Date Posted: January 15, 2008 at 10:05 PM
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.
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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.
Posted By: i am an idiot
Date Posted: January 16, 2008 at 3:53 PM
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.
Posted By: mmcelroy
Date Posted: January 20, 2008 at 12:17 AM
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.
Posted By: mmcelroy
Date Posted: January 20, 2008 at 12:34 AM
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?
Posted By: DYohn
Date Posted: January 20, 2008 at 11:05 AM
Remove the amp from the vehicle and take it to a good shop for testing to find out what's really wrong with it. When output transistors blow there is generally a reason that has nothing to do with the transistor itself, and until you discover that you are wasting your time and money. I am not too sure a Kenwood amp is even worth fixing to be honest with you, so be sure to weigh the cost of repairs VS the cost of a new amp. And no, the power ratings of the gear has nothing to do with anything. ------------- Support the12volt.com
Posted By: Alpine Guy
Date Posted: January 20, 2008 at 4:37 PM
The thing with those power supply transistors is that they all must be replaced at the same time from the exact same batch of transistors, they all went through the same abuse, so they all need to be replaced no matter what unfortunately. But theres so much more to be tested to be sure. You could try replacing them all and see what happens, or you could get it repaired professionally.
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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.
Posted By: i am an idiot
Date Posted: January 20, 2008 at 5:46 PM
He has no problem with the power supply transistors. And his outputs are single outputs. I am wondering if he used heat sink compound and tightened the screws down that hold the outputs in place.
Posted By: mmcelroy
Date Posted: January 21, 2008 at 6:08 PM
Great news! I believe I have fixed the amp, it's been running perfectly since this morning. I think I underestimated the need to properly attach the transistors to the heat sink. This time when I replaced the transistors and reattached the circuit board to the amp's shell I added thermal compound to all of the transistors and made sure that they were all securley fastened down. Thanks for everyone's help. Matt
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