Kicker kx400.1 output mosfets

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Aaron waldrop

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Joined 2019
#1
I have an older kx400 .1 that I repaired with new output mosfets probably a year ago. And unfortunately it has went out again. It had irf640 mosfets from the factory that originally burned out I replace them with all I had on hand which was irf640n. There are two located side-by-side and they are the only two in the amp with this number. I gave the amp back to my little brother and he played it for 3 or 4 months and eventually he said it went back out of course he was probably playing it at below rated 2 ohms. This time I ordered the original irf640 to replace them I have already cut them out of the board and powered on the amp and now the green light comes on I hear it click and it stays on like it should is there anything else I should check before I go further. I did check the voltage with it powered on and if I remember right it was -47to50v on one of the legs can't remember exactly which one but it was the same as last time so I'm assuming the new mosfets will fix it anyone have any input.
 
#3
~47 volts sounds right for the rail voltages.The IRF640 on this amp and others with the same topology, are a weak link and is quite common from this device to fail, usually one will short and replacing both will fix the amp. I recall using IRF640N as a replacement.

If the gate resistors are in tolerance, R224,R226-10Ω and the resistance measured across the outside pads where the IRF640's locators are, is 50kΩ,you should be good to go.

If you have a scope, look at the drive at the gate resistors. If you will post a screenshot and pics of the board, I can advice further, if necessary.
 
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