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Old 26th September 2006, 03:05 PM   #1
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Default Mosfet blown all the time.

I would like to know why my car amplifier's mosfet blown all the time. I have no idea how to mke my amplifier more reliable. When I drive 1 12" subwoofer with my alplifier, I can last around half an hour and the mosfet will blown. I have checked the temperature, it was only around 67-68'C and it was not normal to blow mosfet in this range of temperature I think. Can anyone help me?
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Old 26th September 2006, 05:36 PM   #2
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Could be alot of things here.

Bad ground,
Bad power wire,
Improper fusing,
Too low of a load on the amp,
Low 12 volt DC to the amp
Bad drive voltage to the fets,
A bad gate resistor

Plus 70 degress C is pertty hot, over 150 F so your junction temps would be really out there on your fets. Case temp is relative to the high temp cutoff sensor, and ball park to the internal temp of the fet junction.

Plus you could have one fet failing and dragging the rest down with it, they are banked after all so, "1 down goes all"

You need to post more info like what speaker and voice coils wired how, and what amp and model.

You could have a 50 watt pyramid amp driving a L7 dual wired for 1 ohm for all we know by your description And this combo just won't work for anyone lol lol lol

Send more info please thx
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Old 29th September 2006, 06:17 PM   #3
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Justonemoreamp has a great point.Whats the speaker you are using?What amp?what ohm is the speaker?You might be using the wrong setup and need to set it up different and not so much power.
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Old 29th September 2006, 09:30 PM   #4
adason is offline adason  United States
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maybe its a fake mosfet you are replacing with
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Old 29th September 2006, 10:14 PM   #5
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Was the amp ever reliable? For example, did it perform well for a relatively long period of time (weeks, months...) and only became unreliable after the first time it failed and was repaired?
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Old 1st October 2006, 04:13 PM   #6
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It has no problem at all if you play in moderate volume, but when you push volume up and drive the speaker hard, then the mosfet will burn when the temperature reach around 68'C.
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Old 1st October 2006, 07:45 PM   #7
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Can you provide the 'detailed' history of the work that's been done to the amp each time it has failed.

Also provide information about the make/model of the amp. If possible post a good quality photo of the circuit board. Particularly the area that's been repaired.
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Old 1st October 2006, 11:37 PM   #8
Eva is offline Eva  Spain
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That seems like the result of an incomplete or erratic repair job, repeated again and again.
I use to feel like the small child in The Emperor's New Clothes tale
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Old 2nd October 2006, 07:01 AM   #9
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The temperature of the case is most probably a lost leader in this issue.

Since all mosfets are rated for temps above 100 degress C, and mosfets have the opposite temp coefficient as regular transistors.

So, keep looking, and start looking elsewhere than the "symptom" fet failure as its clearly a by-product of the real failure issue....

Best of luck as always
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