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-   -   Blown IRFZ44N (http://www.diyaudio.com/forums/car-audio/78522-blown-irfz44n.html)

cruck00 28th April 2006 10:14 AM

Blown IRFZ44N
 
I am trying to fix an audiobahn a2300hcx amplifier that had burned out a couple of years back. The amp had pop spilled on it and it went through one of the fans and nothing seemed to happen at that time. The next morning the amp was fired up and it blew out and the protection turned on. I opened up the amp and noticed that three of the mosfets were definitely blown up so I replaced them with new IRFZ44n. There was some blackening on the resistors (gate?) right in front of them so I tested them to check their resistance and they tested out at the proper level. So I reassembled the amplifier and hooked it up to a battery to see if it would function properly and it blew two of the same fets again. One of the fets that I replaced appears to still be in good condition. I removed the two damaged fets and powered the amp up again. The fans and everything turn on but the protection circuit is still on. Can someone please tell me what would cause just these two mosfets to keep blowing up.

TO-3 28th April 2006 03:03 PM

Re: Blown IRFZ44N
 
Quote:

Originally posted by cruck00
I am trying to fix an audiobahn a2300hcx amplifier that had burned out a couple of years back. The amp had pop spilled on it and it went through one of the fans and nothing seemed to happen at that time. The next morning the amp was fired up and it blew out and the protection turned on. I opened up the amp and noticed that three of the mosfets were definitely blown up so I replaced them with new IRFZ44n. There was some blackening on the resistors (gate?) right in front of them so I tested them to check their resistance and they tested out at the proper level. So I reassembled the amplifier and hooked it up to a battery to see if it would function properly and it blew two of the same fets again. One of the fets that I replaced appears to still be in good condition. I removed the two damaged fets and powered the amp up again. The fans and everything turn on but the protection circuit is still on. Can someone please tell me what would cause just these two mosfets to keep blowing up.
An output channel might be bad, have you measured them? If one IRFZ44 blows, you need to replace them all as you are stressing out the part that is not blown.

cruck00 28th April 2006 03:11 PM

I am still new to car audio repair. I work for a large electronics manufacturer so I have the ability but I still have some questions. Are the output channels the ones on the opposite ends of the mosfets?

TO-3 28th April 2006 03:17 PM

Quote:

Originally posted by cruck00
I am still new to car audio repair. I work for a large electronics manufacturer so I have the ability but I still have some questions. Are the output channels the ones on the opposite ends of the mosfets?
Yes. Usually they are complimentary bi-polars. Measure from the middle pin to the outer pins to check if they're shorted. Replace all parallel components and I'd recommend that you replace the complimentary components as well.

cruck00 28th April 2006 03:21 PM

Should I replace the components on the opposite side of the board as well, even though they don't seem to have been affected?

TO-3 28th April 2006 03:24 PM

Quote:

Originally posted by cruck00
Should I replace the components on the opposite side of the board as well, even though they don't seem to have been affected?
No. If the other channel is not shorted you do not need to replace them. These are totally independent of the opposite channel.

cruck00 28th April 2006 03:31 PM

Alright, I will try replacing all of the fets on the bad channel and test the outputs. Then I will replace all of the outputs on that channel. I will also be replacing the resistors for each mosfet and output. I will have to wait a little while before I can actually replace these components because I will have to order some more mosfets and some outputs. Thanks for your help and I will post how everything turns out after I do the repairs.

cruck00 28th April 2006 03:32 PM

are there any other components that you would recommend replacing? and how do I know what wattage of resistor to use when replacing them?

cruck00 28th April 2006 03:39 PM

I do know the current ohm values just unsure about the wattage.

TO-3 28th April 2006 03:59 PM

Quote:

Originally posted by cruck00
Alright, I will try replacing all of the fets on the bad channel and test the outputs. Then I will replace all of the outputs on that channel. I will also be replacing the resistors for each mosfet and output. I will have to wait a little while before I can actually replace these components because I will have to order some more mosfets and some outputs. Thanks for your help and I will post how everything turns out after I do the repairs.
I would check the outputs before you replace the switchers in the power supply. You don't want to keep replacing power supply parts.


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