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Jason Kooner Jason Kooner is offline
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Default infinity overture 2 repair

On Sunday, March 30, 2014 1:37:06 PM UTC-5, Mark Zacharias wrote:
"chuck" wrote in message

...

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.






UGH. Had to work on one of these once. Reminded me of a car amp.

Don't forget to use an isolation transformer.



The manual can be downloaded from Elektrotanya or you can email me at:







and reverse "labolgcbs" to read "sbcglobal".



They do get a number of open resistors. I my case, a predriver looked good

but wasn't. Caused additional heartache. Got it working, but it wasn't worth

the trouble for me. If business hadn't been slow I would have just turned it

away.



Mark Z.





I have the manual now ...thanks. Also I did find some 0.22ohm half watt resistors that were open. There is also one BF469 NPN transistor that is bad but I can't find it online. I tried searching for recommended alternate but no one carries those either...too old.

Can I just lookup the Hfe, voltage and ft on the datasheet and search on mouser od digikey for the same specs? Or does anyone know of a BF496 sub that I can get in 2014?

thanks,

-jason