Question about Rockford Fosgate Punch 401S Car Audio Amplifier

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Rockford Fosgate Punch 401s starts then smokes

I have a Fosgate Punch 401s I got from a friend that had a melted input jack from a loose connection. I put in bolts for the input and there are no shorts now and it has a good power connection. When I start my car even if the stereo and all the amp settings are on low, after about 20 seconds or so the amp stops and starts smoking. When it works, it works just fine, the light comes on and it sounds great. I think it may have something to do with the fact that when I start my car after about 20 seconds, something kicks in under the hood and my dash lights get brighter. I am using the 1200 watt 401s amp, a new stereo, and a 12' Fosgate Kikr 400 watt 4 ohm dual channel sub, and all 8 gauge wiring. The amp has the option of dual or bridged wiring to the sub. Is it possible I am wiring something wrong or maybe is it something to do with that thing under my hood kicking in? Any suggestions on how to troubleshoot this? I am good with wiring and fixing electronics but not as much with how car wiring works so I need help.

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  • Cody Morgan Feb 05, 2009

    I am going to do some testing with it either this afternoon or tomorrow.
    Would the 15 amp fuse work long term? I am not really wanting deafening window shaking bass, just some more feel to the music.
    Also, when I am measuring the voltage, what numbers am I looking for?
    Thanks for the help!

  • Cody Morgan Feb 05, 2009


    I will see what I can do with this.

    Appreciate the help

  • Cody Morgan Feb 12, 2009

    Hey, I did some additional testing on the amp, and I found that it is at least one of the transistors that is fried on the panels connected to the heatsink. I got a schematic from Rockford's site, so is it possible to just replace the defective piece and go with it?

  • Mark Skinner May 11, 2010

    Also like I said I need to know what transistor failed, If you can specify like power supply section or output section. get the number of of it and if it's to fried to see post the number of the one next to it then that will let me know if it's output section or power supply section.

  • Mark Skinner May 11, 2010

    Yes, it is possable to replace the bad transistor and then see if the amp will work. If no other trnsistors were shorted then it should work. Go ahead and try it and if it works I advise you to replace all the transistors on the side it was shorted on. Is it the power supply mosfet or a output mosfet cause I don't know on this paticular amp if the output transistors are mosfets. Lets just say they are power supply mosfets cause the power supply section allways uses mosfets and there are like 3 or 4 in a row with the same number on the front of the transistor on the power supply section. Just replace it and see if it works and let me know then we will go from there. good luck and I'm glad you found the bad on, but make sure the other ones are allright before continuing. Allways double check and triple ckeck if need be cause I do just to be certain. Let me know.

  • Perry Babin May 11, 2010

    Which transistor failed?

    Email me a copy of the schematic if you don't mind. It will make things easier.

  • Mark Skinner May 11, 2010

    I agree with pbabin. But try this if you want cause it'll tell you a lot, disconnect your power wires from the amp and if possable take a 12 volt car battery to where you have the amp mounted, hopefully in the trunk and conect power to the am this way and see what happens. Better yet if you remove amp from car and take it to a place like your garage or where ever you can hook it up like a bench test. Doing this is to rule out any problems with the amp internally and the problem lies in your car wiring. It sounds like, since you allready had smoke coming out that you definately have some internal problems in the amp. Smoke that comes out of a amp is not good and something has fried. Also look for connection where the input was melted and make sure any connections are'nt touching anything else like grounding out. Good luck and let me know what you find.

  • Perry Babin May 11, 2010

    The 15 amp fuse will not hold at full power. It's simply used to determine if the amp is drawing excessive current at idle.

    With the black meter probe on the ground terminal of the amp, you should not read more than 14.5v DC on either the remote or B+ terminals.

    If you find that the amp needs repair, email Rockford to get the schematic for it and send me a copy of it.

  • Perry Babin May 11, 2010

    You need to measure the voltage at the amp to determine if the voltage is going too high.

    It could also be that the voltage is low at first because the amp is drawing excessive current and when it shuts down the voltage comes back up to normal. If you use a 15 amp fuse in the B+ line feeding the amp, it should not blow until you drive the amp hard (high volume). If it blows with no audio, the amp has a defect and is in need of repair.

    If it smokes every time, remove the bottom cover and see if you can identify which component is smoking. If you do this, you MUST wear safety glasses. The components in the rockford have no clamps on them and sometimes, when they fail, they explode throwing very hot pieces of sharp plastic.



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Can somebody email me the schematic for the Rockford Fosgate 401S?

Posted on Apr 29, 2010


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SOURCE: what is the auctual watts fpr the Rockford Fosgate

rockford fosgate doesnt have watts its considered monoblock it gives off watever the speakers gives them the power they need

Posted on Dec 29, 2009

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SOURCE: need to know how many ohms this amp is

Safe down to 2 ohms, NOT a 1 ohm stable amp, it will be pushing it hard even at 2ohms but Fosgate's should be able to handle it providing that the install and all cables,wire,connections,etc. are sanitary!
Good Luck !

Posted on Jun 30, 2010

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