problem with mosfets

rafelo · 11th June 2007, 09:20 AM

Hello, I have a c-audio ST600 and it has mosfets burn.It used 2sk1058 and 2sj162.I have buy news this and I have tested before to mount and all are in shortcircuit beware S and D and I do not mount because I do not understand.I have make a tester circuit for mosfets and it,s the same.Why?Can anybody help me ?Thanks.I have send circuit test that I have used.

Christer · 11th June 2007, 10:57 AM

These transistors have a built in protection diode from S to D, so that is probably what you measure as a short circuit.

rafelo · 11th June 2007, 12:21 PM

Hello, I know that it have a internal diode but I have tested in the 2 direcctions possible and is in short circuit.Thanks for answer

richie00boy · 11th June 2007, 12:28 PM

Make sure you connect gate to source while doing the resistance test. The voltage on your hands will turn the MOSFET on. You might have even damaged them already with this voltage.

VHF man · 11th June 2007, 12:52 PM

I'm pretty sure those mosfets also have a gate protection diode, so they should be OK.

Charles Hansen · 12th June 2007, 04:27 AM

Yes, they have a gate protection diode. So they probably are OK. However, if you measure from gate to another terminal with a voltmeter, it will either turn the device fully on (or fully off), depending on the polarity you applied.

To get a better reading, discharge the gate by touching the gate and one of the other terminals with your fingers. This will bleed off the residual charge and allow an accurate reading. Good luck.

rafelo · 12th June 2007, 08:51 AM

Hello, I know that it have a diode and I have tested in 2 polarity and is in shortcircuit. I have discharge with all posibilities and it,s in shortcircuit. It,s possible damage with fingers? All news mosfets are damage. I do not understand.Thanks

burbeck · 12th June 2007, 09:48 AM

hi there,
are these new parts you are testing? these transistors are fairly rugged i would not expect that you have blown them with static.
have a look at this for testing http://www.4qdtec.com/mostest.html
i think he is talking about n type devices in this example, for p type reverse the leads.
also i find that most multimeters will work on ohms range with this test
regards
bob

AMV8 · 12th June 2007, 12:05 PM

rafelo

If you are going to be working with many mosfets and/or jfets I recommend you buy a semiconductor tester. They cost around us$100 and will recognise and test most types of transistor and fet. They use a few miliamps ( usually 3ma ) to test with and will not damage any of the parts. You can also use them to match parts for most operations.

Don

11th June 2007, 12:28 PM	#4
richie00boy Did it Himself diyAudio Member Join Date: Nov 2003 Location: Gloucestershire, England, UK	Make sure you connect gate to source while doing the resistance test. The voltage on your hands will turn the MOSFET on. You might have even damaged them already with this voltage. __________________ www.readresearch.co.uk my website for UK diy audio people - designs, PCBs, kits and more

12th June 2007, 09:48 AM	#8
burbeck diyAudio Member Join Date: Aug 2004 Location: Ratae Coritanorum	test hi there, are these new parts you are testing? these transistors are fairly rugged i would not expect that you have blown them with static. have a look at this for testing http://www.4qdtec.com/mostest.html i think he is talking about n type devices in this example, for p type reverse the leads. also i find that most multimeters will work on ohms range with this test regards bob __________________ regards bob

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11th June 2007, 10:57 AM	#2
Christer diyAudio Member Join Date: Sep 2002 Location: Sweden	These transistors have a built in protection diode from S to D, so that is probably what you measure as a short circuit.

11th June 2007, 12:21 PM	#3
rafelo diyAudio Member Join Date: Jun 2007	Hello, I know that it have a internal diode but I have tested in the 2 direcctions possible and is in short circuit.Thanks for answer

11th June 2007, 12:52 PM	#5
VHF man diyAudio Member Join Date: May 2007	I'm pretty sure those mosfets also have a gate protection diode, so they should be OK.

12th June 2007, 04:27 AM	#6
Charles Hansen diyAudio Member Join Date: May 2003 Location: Colorado	Yes, they have a gate protection diode. So they probably are OK. However, if you measure from gate to another terminal with a voltmeter, it will either turn the device fully on (or fully off), depending on the polarity you applied. To get a better reading, discharge the gate by touching the gate and one of the other terminals with your fingers. This will bleed off the residual charge and allow an accurate reading. Good luck.

12th June 2007, 08:51 AM	#7
rafelo diyAudio Member Join Date: Jun 2007	Hello, I know that it have a diode and I have tested in 2 polarity and is in shortcircuit. I have discharge with all posibilities and it,s in shortcircuit. It,s possible damage with fingers? All news mosfets are damage. I do not understand.Thanks

12th June 2007, 12:05 PM	#9
AMV8 diyAudio Member Join Date: Jan 2005 Location: near london	rafelo If you are going to be working with many mosfets and/or jfets I recommend you buy a semiconductor tester. They cost around us$100 and will recognise and test most types of transistor and fet. They use a few miliamps ( usually 3ma ) to test with and will not damage any of the parts. You can also use them to match parts for most operations. Don

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