IC251.3

MODIFICATIONS FOR THE ICOM IC251 
SSB & CW VARIABLE POWER 
Place  set  with  the controls towards you  and  remove  lid.  If 
necessary check FM and CW power. Connect set to known good  dummy 
load and power meter.Locate R13 and R14 on the small board behind 
the  front panel RF power control. With RF power control on  max, 
TX  on  FM and adjust RH pot(R13) for  10-12watts.Turn  RF  power 
control  fully down and adjust LH pot(R14) for desired low  power 
setting (min 200mw). Short key jack at rear of set, switch to CW, 
TX  and adjust R129 for 10-12watts the same as on FM. Switch  off 
power.  Locate the brown wire to the left of the Xtal  filter  it 
runs from next to R258 to near R327 its marked with a small b  on 
the  main unit board layout diagram. Cut this wire at  the  front 
end and solder to the emmiter of Q65 or the purple lead marked  I 
on  the main unit layout. Solder the slider of a 4.7k  preset  to 
the LH end of the resistor behind R14,then solder a 3.3k resistor 
to  one leg of the preset, run a wire from this resistor  to  the 
top of R272 (scrape the paint off before attempting to solder). 
Switch on. Switch to CW, TX and with front panel RF power control 
fully  down  adjust the(4.7k preset for desired low  power  level 
(min 200mw) SSB power is the same as CW. The front panel  control 
now affects both FM,CW & SSB power levels. 
VOX ON FM 
Place the set with the controls towards you,remove lid. 
Locate R290 on the main board it is just behind the CW delay control 
cut this resistor and insert a 1N4148 diode in series with it,its 
anode should be away from the resistor.Connect another diode (1N4148) 
to R290 then connect its ano he board on the back of the rf power 
control.
The VOX switch will now work on FM 
EXTENDED FREQUENCY RANGE 
Place the set with the controls facing away from you,remove  lid. 
Locate D52 on the Driver unit (top LH corner on the diagram,  the 
side  nearest  the edge of the set) this will not be  present  in  
solder  a  1N4148  diode in this space. The set  will  now  cover 
143.800 to 148.199mhz on TX and RX 
NB the PI board layout diagram is incorrect in 3 manuals I have seen 
so beware!!!! 
JULIAN G6LOH