Question about Kenwood KAC-8401 Car Audio Amplifier

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Kac-8404 100w amp

I found out that my amps channel 4 out put transistors are bad but i took them out but i dont know which part to replace them with does anyone know what kindof transistors it uses? or how can i find out?

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Re: kac-8404 100w amp

What are the numbers on the transistors?

Posted on Jan 07, 2008

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How do i wire a kenwood amp to two 8in woofers

at low volume any speaker works impedance mismatches wont matter(thats the 4 or 8 ohm resistance speakers have) , but at huge volume you need to consider a crossover circuit in the wired line
or a booster amp that does it for you.
when you have a huge volume level, the coils will feed back (counter emf ) some of that power back into the transistors driving it.
some transistors can die if mismatched badly at power up with high volume level. or disconnect while runnning a load.
depending on the amps design..
hot plugging anything is taking a risk no matter.

see page 8 of your manual below

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your amp output transistors are shorted and protection is activated to protect your amp from bigger damage.if you are confident you can try to open the amp and you should see some burn marks or burnt(blown) transistor and just simply replace him.or take it to repair shop

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Blown something found the problem just need to solve it !

Those black things are likely the MOSFET transistors (the bits that provide the amplification). They likely look similar to these.

Your problem may be deeper than just these units being blown - especially since there are 6 that are gone. Have you been overdriving the amp? Using speakers with the wrong impedence?

Anyway, you can try to see if they have the service manual. You could also try to source new mosfets from online retailers (eg digikey, - just read the numbers printed on them. You may also want to try to determine why they blew in the first place. I have fixed amps where one or two have gone bad because of being overdriven, but 6 makes me think that something else is wrong. Unless the am has a number of MOSFETs serving each channel. Eg, 3 MOSFETS per channel on a 2 channel amp..

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ok i have the same amp and 1 2ohm dvc sub and was woundering the same thing but from futher research and askin sum xsperts. What i found out is that it is only one channel and even tho there are 2 (+) and 2(-) they actually connect inside the amp makein it one . so if u wanted to wire sumthing parralel u wouldnt have to hook wires from one coil to the other on the speaker , u can just hook it up to the amp. so basically both +'s and negatives on the amp are actually one within it so all the power if you only use one set of them and if u wanna add more subs its just easier to add to the amp by using the xtras .

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Amp powers up (switchable) but has absolutely no output

If possible return the amp to the seller for a refund (before you tamper with it).

If that's not possible, the amp will need to be repaired. Do you want to try to repair it yourself?

For the head unit, you need to check the shield ground first. The following page will show you how to perform the test.

Shield Ground Test/Repair

Let me know if you have any other questions.

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Since you haven't received a response, I'll try to help you through the troubleshooting. The amp probably has shorted output transistors but before you start checking components, you need to 'confirm' that you have no bad connections in the power line.

With your multimeter set to DC volts, the black meter lead on the ground terminal of the amp (not on the point where the ground wire connected to the vehicle) and the head unit on (so the amp will have remote voltage applied), touch the red lead alternately to the B+ and remote terminals of the amp. If the voltage goes below ~11 volts when the amp shuts off, you need to check the wiring feeding whichever line is too low.

If the voltage remains near or above 12v, disconnect all speaker wires from the speaker terminals of the amp and disconnect signal cables from the amp. If it powers up normally, the wiring needs to be checked. If it still shuts down, the amp likely has blown output transistors.

Let me know what you find.

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3 Answers

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I have found the problem to my Kenwood KAC-7202. The amps fan was the only thing that would come on thats it. So I started checkin zener diodes cause all transistors checked out fine. So I remember readinf about a guy that had same problem and took it to a shop and they said it was some diodes. Well, thats what I was thinkin or the transformer. It turned out that 1 zener diode was no good, diode D9 1ss133. I took a zener out of an old vcr I use for parts and put it in and the fan came on as usual then the red light. Then I hooked my mp3 player to the rca input and hooked up some speakers and it works great. Hope this helps you other guys with the same problem. Check your zener diodes with a digital volt meter, if you get any measurement other than the reverse impedance which will read between 600 and 1200 ohms some lower or higher and then reverse the leads on your meter and if you get any reading it's no good and the reading will be 0-50 cause mine read 047 ohms.

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check transistor of the unit 1 or 2 tans. bad use a tester. the unit is overload protected. replace the deffecteve parts

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the outputs should be replaced in pairs, there are 2 to 4 pairs, but you sould only need 1 pair replaced. these transistors typically range between 10 to 30 cdn each + labour, look for 1 to 1.5h to replace & test the unit after repair. check your local repair shop for their rates. good luck

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