infinity overture 2 repair
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
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