[Yaesu] FM Receive On FT-757GX

[Christopher (Chris) W. Boone]

Check the DC voltage on the Vcc pin of the 3359...If I recall,
the MAX voltage the NC detector chips use is 7 or 8 volts..
sometimes they have 9 volts on them!! (Spectrum did that in their
early SCR200 series rcvrs)....if so, look for a resistor in series
with that pin and put a 100ohm resistor to gnd at the chip side
of the resistor...this will lower the Vcc to the chip below the max
and prevent it from going south! :)
If the voltage is below 8V DC, but still close to it, it wouldnt
hurt to lower it a little anyway...I hate running ICs near their max!
Chris
WB5ITT

"Melum, Mike" wrote:
> =

> At 06:34 PM 2/15/02 -0800, you wrote:
> >    Thanks for the replies to my message, but I don't think I explaine=
d
> >my situation good enough.
> >    I am able to hear the audio, IF I turn my volume knob all of the w=
ay
> >up.  If it is where it is would be for every other mode (SSB, CW, AM)
> >then I can't hear anything even static.  Another Ham that I know that
> >has the same radio took a look at it (K=D8OJ) and he said that it shou=
ld
> >have at least static where the knob would usually be.  If I turn the
> >knob all the way up then I can hear the stations that are loud enough
> >without any problems.
> >    Thanks again for the replies.
> >    73 de KC=D8LFV (Josh)
> =

> Hi Josh,
> =

> I had the same symptoms.  For FM only, the FT-757 uses a discriminator =
IC,
> the MC3359 (Q22).  Apparently some of these chips have a weak circuit i=
n
> them that tends to fail.  It is the squelch output.  It fails in a mode=

> resulting in the rig permanently squelched.  I eventually removed the c=
hip
> and installed a socket, and put in a new MC3359.  In the interim, you c=
an
> take a real sharp pair of dikes and nip pin 15 on the chip.  This will
> restore your audio, but you will no longer have squelch control on FM (=
only).
> =

> Removing and installing a new chip is a REAL challenge in the tight spa=
ce.
> If you can live without squelch, this might be your solution.
> =

> GL
> =

> Tnx & 73
> =

> Mike, KL6M  BP51dc    Webpage:  http://www.qsl.net/kl6m
> 432 EME - FT-736; FT-767; 9.2 Meter Dish; DEM 0.4dB; 700 WATTS
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