dead output fets?

traw · 23rd December 2006, 04:23 PM

So, got my aleph5 constructed. After testing power supply, hooked up both channels as had made these boards before to test them out and usually meticulous on stuffing.

killed my fuse after starting up, about 1minute after start up. how long does it take for cl40 thermisistor to open up fully?

so, trimmed down to just one channel works fine, minimal to no significant offset. let that run about 45 minutes, heat sinks holding up well.

went back disconnected working channel, connected untested channel.

had tiny tiny puff of smoke, fuse blew about 10 seconds. near the + side first output fet.

they are to3p devices and use alum oxide pads so not suspecting broken insulation like when using silpad etc.

Is it likely to be a damaged output fet? Wondering if damaged it overheading the drain during soldering - seems to soak up more heat than gate or source.

I suppose could replace the mpsa18's while in there to be safe... Can it be powered up with out the irfp240's to test?

chipco3434 · 23rd December 2006, 05:13 PM

how long does it take for cl40 thermisistor to open up fully?
1-2 seconds

i'm too stupid to answer anything else other than the smart guys will ask you to tell them what component got cooked.

Netlist · 23rd December 2006, 08:47 PM

Chances are great that the output or current source mosfet is broken. Replacing it is the easiest way.
Measure the DC voltage across the gate resistors, it should be 0V. If not, the corresponding mosfet is broken. Use a light bulb and a variac if possible.

/Hugo

23rd December 2006, 04:23 PM	#1
traw diyAudio Member Join Date: Sep 2005	dead output fets? So, got my aleph5 constructed. After testing power supply, hooked up both channels as had made these boards before to test them out and usually meticulous on stuffing. killed my fuse after starting up, about 1minute after start up. how long does it take for cl40 thermisistor to open up fully? so, trimmed down to just one channel works fine, minimal to no significant offset. let that run about 45 minutes, heat sinks holding up well. went back disconnected working channel, connected untested channel. had tiny tiny puff of smoke, fuse blew about 10 seconds. near the + side first output fet. they are to3p devices and use alum oxide pads so not suspecting broken insulation like when using silpad etc. Is it likely to be a damaged output fet? Wondering if damaged it overheading the drain during soldering - seems to soak up more heat than gate or source. I suppose could replace the mpsa18's while in there to be safe... Can it be powered up with out the irfp240's to test?

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
improving efficiency with parallel output fets	Davey T	Class D	6	3rd December 2008 04:37 PM
SRPP with FETS, what output stage?	davidallancole	Solid State	18	4th January 2008 05:39 PM
MOS-FETS exclusively, input to output, why Nelson?	Jazzo	Pass Labs	10	29th November 2007 03:53 AM
Biasing output stage FETs	PeteMcK	Solid State	7	7th February 2002 09:37 PM

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read


	Please consider donating to help us continue to serve you. Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving

23rd December 2006, 05:13 PM	#2
chipco3434 diyAudio Member Join Date: Feb 2004 Location: Racine, Wisconsin	how long does it take for cl40 thermisistor to open up fully? 1-2 seconds i'm too stupid to answer anything else other than the smart guys will ask you to tell them what component got cooked.

23rd December 2006, 08:47 PM	#3
Netlist diyAudio Moderator Emeritus Join Date: Jan 2003	Chances are great that the output or current source mosfet is broken. Replacing it is the easiest way. Measure the DC voltage across the gate resistors, it should be 0V. If not, the corresponding mosfet is broken. Use a light bulb and a variac if possible. /Hugo