[SignalOne] Low power output with CX7 series radios-- an new twist

[david bertman]

Hello Everybody --

       Low power output on these units can be caused
by tube aging, incorrect adjustment of R19 on the RF
driver board and incorrect adjustment of the low pass
filters on RF Driver board (L1 and L2) and on the
Front End board (L3 and L4). These all can cause low
outpu, especially on bands above 14mhz.

      Of course, component failure in the transmit
path can cause the problem of low output, but this is
usually NO output.
 
      Other causes are improper adustment of
transmit/receive or 30.2 to 31.2 mixer bandpasses. 
Further down the list would be low levels on any of
the signals that go into the mix, mainly BFO board.
I have seen these kind of problems, but they show up
on receive as well as transmit.  The ones in above
paragraph are exclusively transmit path adjustments.

      SO  -- the above is nothing new.  Smarter S/1
people than I have pointed these things out.  BUT:  I
have discovered a new possibility.  A wiring error!

      This took me longer to find than I would ever
like to admit, and I could have found it in minutes if
I had known what to look for.  The problem is that
Front End board bypass capacitor, c46 is wired
inoorrectly.  There is an extra unused hole on the
board, and one lead of c46 will fit into it perfectly,
thus not going where it should.  This is very easy to
spot:  just match up the components of your Front End
board with those shown on component layout sheets in
section 4 of the manual.  C46 is at the end of narrow
part of board, right next to Q5.  You have the problem
if C46 on your board is at right angles to the one
shown in manual.  

       What this does is fail to bypass the collector
of Q5, which is an emitter follower delivering output
to the RF driver board.  This turns the emitter
follower into a "collector follower", esp. at
frequencies above 14mhz.  The local symptom is FE
board pin 59 output is very low on high frequencies. 
Also, the waveform is somewhat distorted.

       In other words, this radio could never have
worked properly.

       I do not wish for any other radios to have
wiring errors, but just in case  --  

       73,  
            Dave, AB7B