Modifications for the ICOM - RogerK

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 beforeattempting 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.The following modification was carried out to enable the front panel power control to be used on CW/SSB as well as FM.The modification is in two parts (1) the front panel and (2) the main circuit board.(1) FRONT PANELi. Remove four retaining screws and top cover.ii. Remove four retaining screws and bottom cover, disconnecting the speaker.iii. If you have a Mutek front end board fitted remove it now. MAKE NOTE OF THE CONNECTIONS TO IT! ***WRITE ITDOWN***iv. Remove the four front panel frame screwsv. disconnect the wiriing harness and remove the front panel. NOTE WHERE ALL THE PLUGS GO! ***WRITE IT DOWN***vi. Locate the orange wire linking the mode switch and the board behind the power control potentiometer.vii. Desolder it from it's present position on the mode switch and move it to the common side of the switch. That completes thefront panel mod.(2) MAIN CIRCUIT BOARDi. Remove the internal PSU if fitted.ii. Remove the VCO and screening plate on the underside of the main circuit board.iii. Now turn the rig over and find the brown wire that places TX9V(FM) on to Q64/Q65. If you look at the board layout in themanual the wire runs from sectors 3F to 4F and is marked "b".iv. Cut this wire where it joins the board, near R327/R46.v. Now find the purple wire marked "k" on the board layout on the edge of sectors 5F/6F, locate this point on the underside ofthe PCB.I did this by standing the rig on one side panel and shining a light upon the component side of the board. Pointing to thewire with a pencil or radio driver and looking at the track side to see the shadows.vi. Once you have identified the point on the trackside of the PCB desolder the wire and clear the hole that is left.vii. Join the purple and brown wires, then solder them back into the hole from where the purple wire came from. If the brownwire is to short replace it, as I did. I used a purple wire striped from a ribbon cable.This now means that when the radio is switched to transmit TX9V is placed on to Q64/Q65 and not TX9V(FM) as before.That completes the mod.viii. Reassemble the radio in the reverse order to which you disassembled it, leaving the top cover off.ix. The only thing to do now is to check that the rig still works ok and to reset the high and low power levels. This is done byadjusting VR13(high) and VR14(low) with a power meter and dummy load connected to the aerial connector and if possiblea two tone audio generator feeding into the microphone socket at around 600mV should de used to set the rig up on SSB.The power reading on the RMS power meter should be approximately half the PEP. When the desired power levels havebeen set fit the top cover.NOTES:I found that the power control on SSB/CW tends to drop the power off rather quickly but if you use it in conjunction with the micgain control very low power levels are attainable (milliwatts). Since this mod was done, G8RCF Des Sayer has also completed thesame and when we last spoke said he had not experienced any problems. An ALC input is included in the multiway socket on theback apron and if you are going to use the rig with a transverter for 6M, 4M, 70Cm, 23Cm or even HF, I suggest you look at amethod of using this input to control the drive to the external equipment and not the modified power control as it is far too easyto forget to lower the power or to catch the control.The afore mentioned note on ALC apart, this mod is useful to run a linear at a lower out put, e.i. I run my MML100s at 40 wattsor less as this stops breakthrough to a neighbours television set, yet alowing me to gain a higher ERP than just using the rig tofeed in to the aerial.My thanks go to G8RCF who was the second one to modify an IC251 using the method I used to my knowledge. Hope you find