IRFP240 faliure? Help needed!

marijan · 5th April 2003, 12:04 PM

Hello,
A few days ago a recognized increased low freq. hum from my speakers. I cheacked basic parameters on boath chanals of my Aleph 2 monoblocks. All voltages on pcb`s are in service schematic limits (litle higher voltage on R19 on falied chanal - 4,8V acros R19), problem ocures on FET`s PCB board. On one of the fets, the voltage acros the source resistor, raised from normal 0,45V to 2V . All other fets (on + and - chan.) are runing at 0,52volts acros source resistor (cca. 0,45V before faliure). Temperature on heatsinks raised for cca. 2-3°C. There is a noticeable change in sound caracter as well, but boath chanals keep playing. Am I dealing with dead FET?
Thanks
regards
Marijan

Mark A. Gulbrandsen · 5th April 2003, 11:23 PM

I'd just replace the bad FET and see how it behaves then. If this is a new amplifier it may be that you just have a defective device. 2 volts across a source resistor is way too much. Also check it with no input. Perhaps your preamp is throwing out a tiny bit of DC.
Mark

marijan · 6th April 2003, 12:40 PM

Thanks Mark,
it was a lost conection (desolderd joint during the heating of fet I supouse) betven source resistor and source pin on irfp. Everithinng back in normal now. I should go to P2P conection I think.
regards
Marijan

5th April 2003, 12:04 PM	#1
marijan diyAudio Member Join Date: Jul 2002 Location: Slovenija	IRFP240 faliure? Help needed! Hello, A few days ago a recognized increased low freq. hum from my speakers. I cheacked basic parameters on boath chanals of my Aleph 2 monoblocks. All voltages on pcb`s are in service schematic limits (litle higher voltage on R19 on falied chanal - 4,8V acros R19), problem ocures on FET`s PCB board. On one of the fets, the voltage acros the source resistor, raised from normal 0,45V to 2V . All other fets (on + and - chan.) are runing at 0,52volts acros source resistor (cca. 0,45V before faliure). Temperature on heatsinks raised for cca. 2-3°C. There is a noticeable change in sound caracter as well, but boath chanals keep playing. Am I dealing with dead FET? Thanks regards Marijan

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5th April 2003, 11:23 PM	#2
Mark A. Gulbrandsen diyAudio Member Join Date: Sep 2001 Location: Salt Lake City	I'd just replace the bad FET and see how it behaves then. If this is a new amplifier it may be that you just have a defective device. 2 volts across a source resistor is way too much. Also check it with no input. Perhaps your preamp is throwing out a tiny bit of DC. Mark

6th April 2003, 12:40 PM	#3
marijan diyAudio Member Join Date: Jul 2002 Location: Slovenija	Thanks Mark, it was a lost conection (desolderd joint during the heating of fet I supouse) betven source resistor and source pin on irfp. Everithinng back in normal now. I should go to P2P conection I think. regards Marijan

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