Checking FETs in circuit

RJCRAFTS · 25th January 2010, 12:29 AM

Hello All

I have a RF P550.2 amp that has a bad output. Is there a way to test the FETs in circuit? I have measured them best I can in circuit and none appear shorted, but the amp is pulsing on and off and the D5 LED indicating a short condition exisits on the amp board is dimmly lit. I know it's best to remove them to test, but it's almost impossible to unsolder them and I don't want to have to cut them out.

Thanks for the help
Rick M.

nigelwright7557 · 25th January 2010, 12:32 AM

Look for a short across S-D.

Perry Babin · 25th January 2010, 01:21 AM

Do you see a pulsing DC voltage on either channel?

Place the meter probes directly across the terminals for each channel.

25th January 2010, 12:29 AM	#1
RJCRAFTS diyAudio Member Join Date: Oct 2007	Checking FETs in circuit Hello All I have a RF P550.2 amp that has a bad output. Is there a way to test the FETs in circuit? I have measured them best I can in circuit and none appear shorted, but the amp is pulsing on and off and the D5 LED indicating a short condition exisits on the amp board is dimmly lit. I know it's best to remove them to test, but it's almost impossible to unsolder them and I don't want to have to cut them out. Thanks for the help Rick M.

25th January 2010, 12:32 AM	#2
nigelwright7557 diyAudio Member Join Date: Apr 2008 Location: Carlisle, England	Look for a short across S-D. __________________ http://www.murtonpikesystems.co.uk PCBCAD40 pcb design software.

25th January 2010, 01:21 AM	#3
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	Do you see a pulsing DC voltage on either channel? Place the meter probes directly across the terminals for each channel. __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links

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