Yaesu FT-902DM Instruction Manual - page 3
At this part of the vfo, is also located its connector. This is very convenient for several reasons:
1. The vfo output can be sampled directly from this connector (pin#1 and ground) with a small
diameter coax (I used teflon coax for this).
2. The connection of the varicap control circuit can be done right there parallel to TC801
3. Both small caliper coax cables can be passed out of the vfo assembly and metal shield from
a hole already EXISTENT under the connector. You only need to open a cross shape slit
through a thin paper diaphragm over the existent vfo chassis hole, and remove the round
sticker that covers the respective hole on the outer aluminum shield. !!
There, you have the input and output connections for your x-lock exiting the vfo at the best possible
position, to ensure minimal distance between the 2 devices.
The cap I used in series with the varicap of the x-lock was only 1pF. It gives plenty of frequency
adjusting capability to the stabilizer, while being low enough in capacitance as to not create any
"warbling" effect in the Rx audio during the stabilization process. (please refer to the x-lock
instruction manual for more details).
Just put the VFO back in its nest, reversing all the diss-assembly steps, leaving the sampling and
control coax wires long enough so you can trim them to fit their respective places on the stabilizer
after everything is installed and the x-lock is in its final position.
The 12v regulated supply for the x-lock can be drawn from the (+) terminal of the 330uF
electrolytic cap on the counter board. Trim and connect the input – output coax cables and connect
them to the stabilizer.
Now you are almost done....
Take a deep breath, double check your work for any mistakes or omissions and flip the power
switch to ON.. After going through its initialization routine (LED going from red to amber and
finally green) the x-lock should give an instant frequency "jump" on the rig's digital display.
This happens as it applies the 4V voltage to the varicap which in turn will affect the vfo frequency.
Now the rig is free of drift, but the linearity of the analog dial is not as good as it was before the
mod. While one can live with it by just ignoring the analog dial, one does not have to compromise !
Simply note (from the analog dial indication that you had calibrated before removing the vfo) the
frequency difference between before and after the mod. It should be higher by approximately
10Khz with the x-lock vs without it.
Turn the rig up side down, remove its lower cover and completely remove the memory unit. Also
remove the Xtal unit, but do not unplug it. Just set it aside (on top of the metal shield of the IF
trimmers works best).
Now you are looking at the under surface of the VFO aluminum shield. You will see 2 round self
adhesive metallic tape parts, covering the respective holes for the TC 801 and L801. You need to
temporarily remove the round tape from the LEFT hole (face of the rig towards you).
This will give you access to the TC801. Turn the rig on and simply adjust TC801 clockwise to
return the digital frequency back to the same indication as the analog one or to reverse the
frequency difference that the x-lock varicap circuit has created .
NOW you are DONE.
Assemple your super stable FT-902(1)DM and enjoy DRIFT FREE QSOs for ever he he.
73s to all
Marinos, sv9dru / ki4gin