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IC-821 Inquiry



Hi Fellows,

I am interested in how the IC-821 gets its 9600bps output.  Is there
someone out there who has an IC-821 and a scanner who could scan the
discriminator section of the schematic showing the circuitry that leads to
the 9600 audio output.  Either Band would be fine.  If so, please drop me a
line and I will get one of you to send it to me.  I'm interested in how
this output is coupled to the discriminator.

Also, it seems that my concern about the hot pass transistor is no real
problem.  It seems that these transistors do run hot.  It is rated at 750mw
and is drawing 620mw.  I have seen two additional units and they are
running hot also.  However, while I was poking around in the radio I
discovered a dead -5.1v supply.  This supply controls the TX power output. 
It is supplied to the RF Out control on the front panel and also to the APC
circuits to keep the power within safe limits.  The power out control did
not control the power and the TX power out was 100 watts from the 75 watt
transmitter.  Fortunately I used it primarily for receiving the pacsats. 
Now that is fixed and I am back in service again.

The -5.1v failure also happened in my IC-275 a year ago and was caused by
the same electrolytic capacitor in both radios.  For you IC-475/IC-275
owners, it is C137 a 10mF, 16v electrolytic on pin 8 of IC8 in the small
open top shielded box on the rear corner of the Main Board next to the key
jack.  Maybe this will save you some trouble shooting if you have this same
failure.

-- 
73, Roy

Internet: w0sl@amsat.org
Home Page: http://home.swbell.net/rdwelch
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