From: jjkooner@gmail.com
On Monday, March 31, 2014 3:19:13 PM UTC-5, chuck wrote:
> On Mon, 31 Mar 2014 10:19:55 -0700 (PDT), Jason Kooner
>
> wrote:
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>
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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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> >>
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> >> news:ag1bj9ld72u9vvplr531cq967mhh7hor9c@4ax.com...
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> >>
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> >> > On Thu, 27 Mar 2014 21:23:14 -0700 (PDT), Jason Kooner
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> >>
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> >> > wrote:
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> >> >
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> >>
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> >> >>Hello,
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> >>
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> >> >>
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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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> >>
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> >> >>to power the woofer section. However, I don't here anything from the
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> >>
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> >> >>woofer. There is a midrange and tweeter that are not powered and they
work
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> >>
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> >> >>fine.
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> >>
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> >> >>
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> >>
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> >> >>I unplugged one of the speakers and opened it up. There is some black
dust
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> >>
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> >> >>on the pcb near the power fets. There are 4 fets and they are all
shorted.
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> >>
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> >> >>The fets are Fairchild IRFS250B. I couldn't find these (too old) so I
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> >>
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> >> >>replaced them with ST Micro STW40NF20 fets. Also the power fets are
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> >>
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> >> >>grouped in 2 pairs with one pair having an NPN transistor between them,
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> >>
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> >> >>why doesn't the other power mosfet pair have this NPN transistor? The
NPN
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> >>
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> >> >>is a Fairchild 2012, it measures ok with a meter but I went ahead and
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> >>
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> >> >>replaced it anyway.
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> >>
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> >> >>
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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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> >>
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> >> >>terrible, it's all distorted. The midrange and tweeter are fine.
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> >>
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> >> >>
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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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> >>
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> >> >>to take some more measurements.
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> >>
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> >> >>
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> >>
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> >> >>Questions:
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> >>
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> >> >>
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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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> >>
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> >> >>comparsion and didn't see anything special about the Fairchild fet.
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> >>
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> >> >>
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> >>
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> >> >>2. Does anyone have a schematic for this pcb?
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> >>
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> >> >>
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> >>
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> >> >>3. What other parts should I look at?
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> >>
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> >> >>
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> >>
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> >> >>I think I was too quick to clean the black dust and should off spent
some
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> >>
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> >> >>more time trying to figure out the source!
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> >>
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> >> >>
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> >>
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> >> >>Cheers!
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> >>
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> >> >>
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> >>
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> >> >>-jason
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> >>
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> >> >
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> >>
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> >> >
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> >>
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> >> > Check for open resistors and open drive transistors.
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> >>
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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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> >>
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> >>
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> >>
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> >> The manual can be downloaded from Elektrotanya or you can email me at:
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> >>
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> >>
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> >>
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> >> mzacharias@labolgcbs.net
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> >>
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> >>
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> >>
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> >> and reverse "labolgcbs" to read "sbcglobal".
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> >>
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> >>
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> >>
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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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> >>
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> >> the trouble for me. If business hadn't been slow I would have just turned
it
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> >>
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> >> away.
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> >>
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> >>
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> >> Mark Z.
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> >
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> >
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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.
>
> >
>
> >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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> >
>
> >thanks,
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> >
>
> >-jason
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>
>
>
>
> NTE108. Mouser Electronics or MCM may have it in stock.
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.
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.
I do have 2 questions:
1. On page 32/35 of the schematic there is a 2K pot in the near the middle of
the page. I assuming this is used to adjust the bias of the power stage to
some level. I have a function generator to help with this, where should I
place my scope probes when
adjusting this pot and what am I looking for?
http://elektrotanya.com/infinity_overture_2.pdf/download.html
2. On the same page there is a 1K 2W (R68) resistor on one of the relay
contacts, what is this for?
thanks,
-jason
--- SoupGate-Win32 v1.05
* Origin: you cannot sedate... all the things you hate (1:229/2)
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