FT470.17
 
When there is more than one combination which has the same frequency
range, the difference is the default step size and/or the default
repeater offset.  Of course, choices that do not match the VCO and
filters do not actually transmit or receive on those frequencies.
A particularly strange example is that the VHF side of the set can
be set to tune from 404 to 444 Mhz, but again, it won't actually lock.
Even in the 101-141 mode, the VHF VCO will not lock - this must be for
use with some other sort of VCO  (It looks like this would cover the
aeronautical band rather nicely.)   There are two really wierd VHF
settings, those for 8AL-242 and 1R3-158L.  These must be for use
with some other LCD controller - it displays truly unusual and
non sequential things when stepped through the "bands".
 
R74 seems to have something to do with something like selecting
the IF frequency, or something else like that.  When set, it
really screws up the VHF reception.
 
My technique for determining these straps is to remove the straps
that come in the unit, solder wires to each pad, run the wires out
of the unit to a bank of DIP switches,  screw the unit back together,
and then go through all of the DIP switch combinations.  I usually
use a stereo microscope and 30 guage wire for this.  Since I didn't
try powering the unit on with every combination of keys held down
for each DIP switch combination, there may still be other secrets
possible.
 
Since I was looking for something like receive and transmit from
zero to infinity, and I didn't find it, I kept looking until I got
bored and wanted to button the thing up and start using it.  I
determined, from studying the schematic, that there should be a
hiddem strapping diode from CPU pin 2 to CPU pin 22.  I installed
one, but nothing changed.  In fact, changing it and powering the
unit up did not cause a reset.  Therefore, I concluded that this
really wasn't a mystery strap, afterall.  However, there could be
others.  I'm trying to get a data sheet for the CPU, from Hitachi,
to see if any of the grounded pins are actually I/O pins -- they
might be good candidates, particularly if their traces are routed
in such a way as to be easily accessible for cutting.
CONT IN FT470.9