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chuck chuck is offline
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Default infinity overture 2 repair

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.