Mosfet Transistor question

orbanator7577 · 23rd January 2012, 11:53 PM

I have two dead transistors IRFP9240 and IRF9610. I tested them and I am not getting any reading from them. Can I just replace them with new or do I have to replace all of them?

nigelwright7557 · 24th January 2012, 12:00 AM

You wont get a reading from them unless they are dead.

They usually go short from D-S and sometimes gate to D or S.

Test them all for shorts.

orbanator7577 · 24th January 2012, 12:03 AM

All of them but those two I am getting readings. I checked and rechecked just to make sure. It is my fault too. I recapped the amp and had two wires switches. Left channel works fine and the right blows fuses. I have been checking the values to everything on the board.

nigelwright7557 · 24th January 2012, 12:08 AM

A lot depends on what damage the swapped wires caused.
Sometimes just replacing damaged mosfets works and other times they just blow again if you havent fixed all the faults on previous stages.

If it is blowing fuses then it sounds like blown mosfets. The only other thing capable of blowing fuses is a power supply fault.

orbanator7577 · 24th January 2012, 12:11 AM

The power supply is good as the other channel is working fine. I did some reading and you confirmed it that a dead mosfet will cause the fuses to blow.

Now, can I just order one of each or is it a good idea to replace all of them?

nigelwright7557 · 24th January 2012, 12:14 AM

Quote:

Originally Posted by orbanator7577

Now, can I just order one of each or is it a good idea to replace all of them?

I would just replace the dead ones. So long as the others dont have shorts they should be ok.

orbanator7577 · 24th January 2012, 12:16 AM

Thanks for your assistance. I'm a novice, but learning real fast and I find it very interesting. I recapped my rotel pre and wow it sounds so much better.

orbanator7577 · 24th January 2012, 12:18 AM

Thats what I will do. Thanks again.

nigelwright7557 · 24th January 2012, 12:25 AM

Quote:

Originally Posted by orbanator7577

Thats what I will do. Thanks again.

It should fix it.
I usually find blown mosfets are all that is wrong.

I dont want to get too technical but sometimes something else can be taken out to further back in the circuit with the mosfets
If i replace the mosfets and they blow again I take out all the mosfets and wire the VAS output back into the ltp and this closes the loop for testing the amplifier. I can then check for dc bias and offset.

diy didi · 24th January 2012, 08:26 AM

I wouldn't just replace those ones that are fried. They need to be matched- all of them. If you replace only the ones that are fried with diff production date ones, chances are that you will be sacrificing reliability. Also from experience, always desolder Mosfets when testing. For some reason they can test no-short when in circuit. Maybe someone can tell me why?

24th January 2012, 12:00 AM	#2
nigelwright7557 diyAudio Member Join Date: Apr 2008 Location: Carlisle, England	You wont get a reading from them unless they are dead. They usually go short from D-S and sometimes gate to D or S. Test them all for shorts. __________________ http://www.murtonpikesystems.co.uk PCBCAD40 pcb design software.

24th January 2012, 12:08 AM	#4
nigelwright7557 diyAudio Member Join Date: Apr 2008 Location: Carlisle, England	A lot depends on what damage the swapped wires caused. Sometimes just replacing damaged mosfets works and other times they just blow again if you havent fixed all the faults on previous stages. If it is blowing fuses then it sounds like blown mosfets. The only other thing capable of blowing fuses is a power supply fault. __________________ http://www.murtonpikesystems.co.uk PCBCAD40 pcb design software.

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24th January 2012, 12:03 AM	#3
orbanator7577 diyAudio Member Join Date: Dec 2011 Location: San Antonio, TX	All of them but those two I am getting readings. I checked and rechecked just to make sure. It is my fault too. I recapped the amp and had two wires switches. Left channel works fine and the right blows fuses. I have been checking the values to everything on the board.

24th January 2012, 12:11 AM	#5
orbanator7577 diyAudio Member Join Date: Dec 2011 Location: San Antonio, TX	The power supply is good as the other channel is working fine. I did some reading and you confirmed it that a dead mosfet will cause the fuses to blow. Now, can I just order one of each or is it a good idea to replace all of them?

24th January 2012, 12:16 AM	#7
orbanator7577 diyAudio Member Join Date: Dec 2011 Location: San Antonio, TX	Thanks for your assistance. I'm a novice, but learning real fast and I find it very interesting. I recapped my rotel pre and wow it sounds so much better.

24th January 2012, 12:18 AM	#8
orbanator7577 diyAudio Member Join Date: Dec 2011 Location: San Antonio, TX	Thats what I will do. Thanks again.

24th January 2012, 08:26 AM	#10
diy didi diyAudio Member Join Date: Sep 2009 Location: Pretoria	I wouldn't just replace those ones that are fried. They need to be matched- all of them. If you replace only the ones that are fried with diff production date ones, chances are that you will be sacrificing reliability. Also from experience, always desolder Mosfets when testing. For some reason they can test no-short when in circuit. Maybe someone can tell me why?

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