[R-390] Using Break-In

[Ed G]

Hi Folks,
     From reading about the break-in feature of the 390A, I *think* it works
like "receiver muting" does on more modern receivers, but I wanted to get
some other opinions. If I leave the front panel break-in switch off, I
believe the 390 just keeps receiving (with no connections to TB103 pin 9),
correct?  If I turn the front panel break-in switch on, what have I enabled
circuit-wise?  Can I then ground the rear panel TB103 pin 9 and have the
receiver mute, or does the receiver then just ground the antenna inputs, but
allow me to hear the transmitter?
     I guess the term "break-in" is slightly confusing, as I doubt this is
really full QSK.
--Ed G--