From: jjkooner@gmail.com
On Monday, April 7, 2014 9:55:19 AM UTC-5, chuck wrote:
> On Sun, 6 Apr 2014 20:59:26 -0700 (PDT), Jason Kooner
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> wrote:
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> >On Monday, March 31, 2014 3:19:13 PM UTC-5, chuck wrote:
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> >> On Mon, 31 Mar 2014 10:19:55 -0700 (PDT), Jason Kooner
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> >> wrote:
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> >> >On Sunday, March 30, 2014 1:37:06 PM UTC-5, Mark Zacharias wrote:
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> >> >> "chuck" wrote in message
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> >> >> news:ag1bj9ld72u9vvplr531cq967mhh7hor9c@4ax.com...
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> >> >> > On Thu, 27 Mar 2014 21:23:14 -0700 (PDT), Jason Kooner
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> >> >> > wrote:
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> >> >> >>Hello,
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> >> >> >>
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> >> >> >>I have a pair of infinity overture 2 speakers. They have an internal
amp
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> >> >> >>to power the woofer section. However, I don't here anything from the
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> >> >> >>woofer. There is a midrange and tweeter that are not powered and
they work
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> >> >> >>fine.
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> >> >> >>I unplugged one of the speakers and opened it up. There is some
black dust
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> >> >> >>on the pcb near the power fets. There are 4 fets and they are all
shorted.
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> >> >> >>The fets are Fairchild IRFS250B. I couldn't find these (too old) so
I
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> >> >> >>replaced them with ST Micro STW40NF20 fets. Also the power fets are
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> >> >> >>grouped in 2 pairs with one pair having an NPN transistor between
them,
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> >> >> >>why doesn't the other power mosfet pair have this NPN transistor?
The NPN
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> >> >> >>is a Fairchild 2012, it measures ok with a meter but I went ahead
and
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> >> >> >>replaced it anyway.
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> >> >> >>
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> >> >> >>I plugged in the speaker and tested it. The woofer is alive now but
sounds
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> >> >> >>terrible, it's all distorted. The midrange and tweeter are fine.
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> >> >> >>
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> >> >> >>I plan to bring a scope and thermal camera home from work for the
weekend
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> >> >> >>to take some more measurements.
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> >> >> >>Questions:
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> >> >> >>
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> >> >> >>1. Was that wrong to sub in the ST Micro fets? I did a datasheet
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> >> >> >>comparsion and didn't see anything special about the Fairchild fet.
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> >> >> >>
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> >> >> >>2. Does anyone have a schematic for this pcb?
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> >> >> >>3. What other parts should I look at?
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> >> >> >>I think I was too quick to clean the black dust and should off spent
some
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> >> >> >>more time trying to figure out the source!
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> >> >> >>
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> >> >> >>Cheers!
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> >> >> >>-jason
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> >> >> >
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> >> >> > Check for open resistors and open drive transistors.
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> >> >> UGH. Had to work on one of these once. Reminded me of a car amp.
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> >> >>
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> >> >> Don't forget to use an isolation transformer.
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> >> >> The manual can be downloaded from Elektrotanya or you can email me at:
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> >> >> mzacharias@labolgcbs.net
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> >> >> and reverse "labolgcbs" to read "sbcglobal".
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> >> >> They do get a number of open resistors. I my case, a predriver looked
good
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> >> >> but wasn't. Caused additional heartache. Got it working, but it wasn't
worth
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> >> >> the trouble for me. If business hadn't been slow I would have just
turned it
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> >> >> away.
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> >> >> Mark Z.
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> >> >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.
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> >> >
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> >> >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?
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> >> >
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> >> >thanks,
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> >> >-jason
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> >>
>
> >> NTE108. Mouser Electronics or MCM may have it in stock.
>
> >
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>
> >I replaced the bad components but it failed again. I think I missed a few
1K fusible resistors that are open. They connect to the gates of the power
fets so I think the gate was floating on 2 fets when I fired it up.
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> >
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> >I'll replace all the bad parts again but this time I'll bring it up slowly
at my work since I have better equipment there.
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> >
>
> >I do have 2 questions:
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> >
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[continued in next message]
--- SoupGate-Win32 v1.05
* Origin: you cannot sedate... all the things you hate (1:229/2)
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