Some answers:
>>First I would like to know how can one damages a MOSFET?
Several ways: put more current thru it than it is rated for, put more voltage on its terminals than it is rated for, put a high surge voltage on its gate during power-on, for example, open the lid of your power amp & without adequate ground shielding for yourself touch something in the amp, create a spark that could fry the circuit (& yourself!). For now, this is my short list.
>>Can wrong connection from powersupply kill it?
Yes, it's possible. However, the MOSFET must have been installed in the factory. It must has passed QC where they would have caught this wrong connection & fixed it before shipping.
IFFFFFF somebody else or you have tinkered with the MOSFET then it *could* be soldered in there incorrectly.
However, if the MOSFET connections are flipped it is unlikely to turn on as the most of the MOSFETs used are enhancement devices which need a positive gate-source or source-gate voltage to conduct. It *seems* that a bad connection is unlikely but........possible.
>>Next up is how does a damaged MOSFET sounds
You should hear lots of distortion like a voice over a crackling radio or a bad AM reception.
I personally doubt that a bad MOSFET will put out any sound 'cuz when there is a catastrophic failure in MOSFETs, these devices fail totally.
MOSFET aging is gradual like many other devices but in my experience failure is total i.e. it's a 0 or 1 situation.
>> how can one knows which one is dead if there are more than one in a poweramp?
This could be risky business as the power supply caps store a lot of energy EVEN when the power amp is disconnected from the wall. Be VERY careful of putting your hand in there - you could create a spark that could fry you or a good part of your hand!
Get a tech/Adcom to trouble-shoot this for you. You'll need a voltmeter to check MOSFET output voltages, bias voltages, etc. You'll also *might* need a schematic.
>>Finally, if there such a thing as life span of a MOSFET?
Yup! there most certainly is! Life of a power MOSFET is usually pretty damn long - 10 years is not uncommon with the multiple on/off cycles where the devices heats up from stone cold. Today's MOSFETs might be hardier.
I think that it might be some other component in the amp such as an aging electrolytic circuit cap or one or more of the power supply caps.
>>First I would like to know how can one damages a MOSFET?
Several ways: put more current thru it than it is rated for, put more voltage on its terminals than it is rated for, put a high surge voltage on its gate during power-on, for example, open the lid of your power amp & without adequate ground shielding for yourself touch something in the amp, create a spark that could fry the circuit (& yourself!). For now, this is my short list.
>>Can wrong connection from powersupply kill it?
Yes, it's possible. However, the MOSFET must have been installed in the factory. It must has passed QC where they would have caught this wrong connection & fixed it before shipping.
IFFFFFF somebody else or you have tinkered with the MOSFET then it *could* be soldered in there incorrectly.
However, if the MOSFET connections are flipped it is unlikely to turn on as the most of the MOSFETs used are enhancement devices which need a positive gate-source or source-gate voltage to conduct. It *seems* that a bad connection is unlikely but........possible.
>>Next up is how does a damaged MOSFET sounds
You should hear lots of distortion like a voice over a crackling radio or a bad AM reception.
I personally doubt that a bad MOSFET will put out any sound 'cuz when there is a catastrophic failure in MOSFETs, these devices fail totally.
MOSFET aging is gradual like many other devices but in my experience failure is total i.e. it's a 0 or 1 situation.
>> how can one knows which one is dead if there are more than one in a poweramp?
This could be risky business as the power supply caps store a lot of energy EVEN when the power amp is disconnected from the wall. Be VERY careful of putting your hand in there - you could create a spark that could fry you or a good part of your hand!
Get a tech/Adcom to trouble-shoot this for you. You'll need a voltmeter to check MOSFET output voltages, bias voltages, etc. You'll also *might* need a schematic.
>>Finally, if there such a thing as life span of a MOSFET?
Yup! there most certainly is! Life of a power MOSFET is usually pretty damn long - 10 years is not uncommon with the multiple on/off cycles where the devices heats up from stone cold. Today's MOSFETs might be hardier.
I think that it might be some other component in the amp such as an aging electrolytic circuit cap or one or more of the power supply caps.