[ICOM] Pro II vs. Pro III RX-ANT input circuit (was "Smoked ProII")

[Adam Farson]

On researching this topic a little further, I noted that the 756Pro and
756Pro2 RF Unit boards had a fuse bulb (DS111) in the RF signal path from
the RX-ANT jack to the ANT/ANT-R selection relay. This has been omitted in
the Pro3. Interestingly enough, though, the Pro3 RX-ANT circuit incorporates
an RF sensor (D101, Q103, Q104) which operates the ANT/ANT-R relay (RL-101)
when RF is applied to the RX-ANT socket, thereby breaking the RF-ANT signal
path. This feature is lacking in the Pro2.

I shall create a web page addressing this. It will be linked from my Pro III
User Review.

http://www.qsl.net/ab4oj/icom/ic756pro3/pro3notes.html

References: 

IC-756Pro3 Service Manual, p. 10-12, RF-B Unit Schematic

IC-756Pro2 Service Manual, p. 10-8, RF-A Unit Schematic

Cheers for now, 73,
Adam VA7OJ/AB4OJ


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