From: chuck@deja.net   
      
   On Thu, 27 Mar 2014 21:23:14 -0700 (PDT), Jason Kooner   
    wrote:   
      
   >Hello,   
   >   
   >I have a pair of infinity overture 2 speakers. They have an internal amp to   
   power the woofer section. However, I don't here anything from the woofer.   
   There is a midrange and tweeter that are not powered and they work fine.   
   >   
   >I unplugged one of the speakers and opened it up. There is some black dust on   
   the pcb near the power fets. There are 4 fets and they are all shorted. The   
   fets are Fairchild IRFS250B. I couldn't find these (too old) so I replaced   
   them with ST Micro    
   STW40NF20 fets. Also the power fets are grouped in 2 pairs with one pair   
   having an NPN transistor between them, why doesn't the other power mosfet pair   
   have this NPN transistor? The NPN is a Fairchild 2012, it measures ok with a   
   meter but I went ahead    
   and replaced it anyway.   
   >   
   >I plugged in the speaker and tested it. The woofer is alive now but sounds   
   terrible, it's all distorted. The midrange and tweeter are fine.   
   >   
   >I plan to bring a scope and thermal camera home from work for the weekend to   
   take some more measurements.   
   >   
   >Questions:   
   >   
   >1. Was that wrong to sub in the ST Micro fets? I did a datasheet comparsion   
   and didn't see anything special about the Fairchild fet.   
   >   
   >2. Does anyone have a schematic for this pcb?   
   >   
   >3. What other parts should I look at?   
   >   
   >I think I was too quick to clean the black dust and should off spent some   
   more time trying to figure out the source!   
   >   
   >Cheers!   
   >   
   >-jason   
      
      
   Check for open resistors and open drive transistors.   
      
   --- SoupGate-Win32 v1.05   
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