Question about Kenwood KAC-729S Car Audio Amplifier

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The easiest is likely when the fets blow, then you replace them and the resistors. But other things can go like drivers and protection circuits you have to track down and replace. Often the power supply will blow because of another reason. You never know what you will find, but some amps do tend to blow 'X' over and over again.

Posted on Apr 22, 2008

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Amp want turn on

Listen everyone who is having any JL 500/1 or 1000/1 amps. There are many reasons why your amps have failed. Most of the problem is the power supply mosfets shorted out and output mosfets shorted too. Those are the 2 biggest problems when you run these amps hard. Also the main power supply capacitors and the gate resistors mostly burn out when a power supply mosfet shorts. Some people if they remove the back cover may see signs of of the problem area and others will not. I have been repairing these paticular amps at least 2 to 3 a week with other amps I get in. It seems that the older ones people bought working are now failing. So this is just a quick overview of what your problem is and is part or is the problem guaranteed. Sometimes I get tired of seeing them coming in but it's what I do and know exactly where to start. I don't know at this time but I think for $160 if you send your JL 500/1 to JL they will just replace the board. Don't quote me on that cause prices change. I would call and ask. My repair depending on the damage is around $80-90 to repair these 500/1. The 1000/1 can be the same or higher. I can't tell you if I don't have it in front of me diagnosing it. As I said though, the problems are basicly the same for the most part and the amp will have to be repaired. I help people also who are electronicaly inclined and if they feel confident and can unsolder and solder and know thier way around a volt ohm digital meter I can walk them through the steps. It's not that hard everybody, really it is'nt. A little confidence and soldering and reading a volt meter and you can repair your own amp. Contact me if you need any help. Thank you!

Jan 13, 2012 | Jl Audio 500/1 Car Audio Amplifier

3 Answers

My amp started to smoke, and cut off,had a real loud burning smell,has not worked since.

Sounds like it was playing? If it was your voltage dropped and the mosfet power supply got toasted. These amps are notorius for burning up at low voltage. Kicker did not put a low voltage shut off on it.,

Sep 08, 2011 | Kicker ZX15001 1Channel Car Amp

1 Answer

Protection mode is on and I don't know why... Red light on the amp

Protection mode normally actives due to too much current being drawn by the output amplifiers. This can be caused by improper loading ( impedance too low for amp to drive) or one or all of your output transistors are blown. The protection mode monitors the power supply current and thermal properties of the power amp. Since your problem happens when it turns on I would have to say the supply is drawing too much current because of a bad output transistor. Without troubleshooting the amp this is the best answer I can give you. Good luck!

Jul 19, 2011 | Sony XMGTX1852 Car Amp

1 Answer

New amp

Something is def. wrong. did you check the fuses on the amp after the light went out? probly have a bad connection somewhere. check ground wire and power make sure they have a good connection and arent cut up and shorting out.

Oct 21, 2009 | Pioneer Car Amplifier GM-7100M - Mono Bass...

2 Answers

Too many repairs

sounds like you power supplies (mosfets) are bad

Jul 11, 2008 | Crate SPA1600 Power Amplifier - SPA Series...

1 Answer


Since I do not have the amp opened up on the test bench and connected to be able to take readings, I can only speculate.

It is obvious by your description that the amp is going in to protection mode. It is possible that the total impedance is too low, or that the amp is being over driven.

If there is some distortion occuring especialy at a high level, the amp should go in to protection mode. It is also possible to have some defective components that are making the amp too sensitive to go in to protection mode. I have also seen defective components intermaly in amplifier units that have caused the power supply to go in to the protect mode.

I have seen defective crossovers in speaker units also cause an amplifier to go in to protection, or even be damaged. If the crossover has the type of defect that is causing an impedance missmatch or be in a low resistance, this can cause the amplifier to go in to protection.

You will need an experienced tech who knows the model of amp very well, has the instruments, and has the service mauals in order to be able to go through it to find the exact fault.

Considering the circumstances, this is the best I can do for you.

Jerry G.

Jun 11, 2008 | Kenwood KAC-9152D Car Audio Amplifier

1 Answer


If the amp blows a fuse with no remote voltage applied, the amp has a short in the primary side of the power supply. If the fuse only blows after remote voltage is applied, the amp probably has shorted output transistors.

May 02, 2008 | Boss Riot 1500D Car Audio Amplifier

1 Answer

Component for amplifier

All of the components with the IRFZ44N part numbers are the same. The rest of the information is the date/manufacturing code and isn't really important (although they should match if they were all used in the power supply). Digikey has them. The new lead free version is IRFZ44NPBF. The rectifier ->

Sep 17, 2007 | Audiofonics ADF-243 Car Audio Amplifier

1 Answer

Power Problem, LED Lights up and then shuts off

Do you have the switch or activate wire on the new amp. to the right hookup? If you do, then theres a problem with the amp and if your not a tech these can be a difficult thing to trouble shoot. Take back the amp or seek out a pro to test it on a bench. Good Luck

Jul 24, 2006 | American Pro VS1405 Car Audio Amplifier

1 Answer

My JL audio 1000/1 amp does not work

Best bet is to send it back to JL, they do not sell the PCB with all of the components loaded on it. Most likely the transistors in the power supply have fried. Open it up and see if you can find any physical damage. Google the part numbers of the bad parts, and you should be able to fix it relatively easily. is a great place for parts. Read this for more testing procedure: The whole site is wonderful, really.

Jun 30, 2006 | Jl Audio 1000/1 Car Audio Amplifier

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