# Nakamichi PA-200 keeps blowing the supply mosfets



## KSakai (Jul 31, 2015)

hello there

Last year, i bought Nakamichi PA-200 amp and it works just fine..I also replaced every electrolytic caps since i thought they might dried out

but around 5 months ago, it started to stop working. turned out that the supply mosfet were shorted. changed it and works fine..... until the next morning i turn it on and NOTHING HAPPENED! 

pulled this thing out and check it again, those mosfets died again!

at least i replaced those mosfets more than 3 times wasting my time to pull and re-install the amp 

I wonder what happened to this amp?.. it plays nice just after a replacement!

mosfets are IRFZ44N, PWM generator is TL494.

thanks in advance!


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## TrickyRicky (Apr 5, 2009)

Replace the mosfet predrivers and the pwm ic.


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## KSakai (Jul 31, 2015)

i'll do it maybe on Tuesday.. i should buy the mosfets, drivers and controller :blush:

anyway is it fine if i use IRF3205 if i can find one?..i'm sure it does nothing but i thought more headroom is good :blush:


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## TrickyRicky (Apr 5, 2009)

You can use the IRF3205's just make sure your gate resistor is within 33ohm-100ohm. 

I don't know if that amplifier uses mosfet predrivers, so trace the squarewave outputs from the PWM pins and see for yourself.


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## KSakai (Jul 31, 2015)

the drivers are 2SA1266..small BJTs
waveform from 494 itself wasnt a good sqwv and from the drivers i can say it's completely horrible :blush:


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## TrickyRicky (Apr 5, 2009)

I would replace what I mentioned earlier....PWM IC, Mosfets, mosfets predrivers, gate resistors and test with a small 5-10 amp fuse just in case there is something else wrong with it.

Were you getting audio when it was working? If so you could cancel the amplifier section and concentrate on the power supply side.


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## KSakai (Jul 31, 2015)

okay.. i'll buy the parts tomorrow 

yes, i got a clean audio everytime i replace the mosfets


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## TrickyRicky (Apr 5, 2009)

Just curious, were are you buying your components from (hoping not from ebay, as that may be the reason why they keep failing).


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## KSakai (Jul 31, 2015)

i bought them from local store..
i actually still guessing if they're fake or original IRFZ44N

any clue for fake/original mosfets?..some of mine were labelled pretty bad like off center, bigger fonts, etc


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## TrickyRicky (Apr 5, 2009)

Order them from mouser, digikey, or arrow electronics. Stores may be generic NTE crap. I have a couple irf3205 if you wanna try those..let me know how many you need , they cost about a buck each, just notice were your from...so you should have suppliers in your country just don't know how reliable or if genuine.


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## KSakai (Jul 31, 2015)

i forgot to buy the parts yesterday :blush:

i was too concentrated on my DIY amp lol


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