Modifications for the ICOM - RogerK

19-07-1998(IC-281) Extended Receive for IC-281To enable extended receive a jumper has to be removed. To enable extended transmit a diode has to be removed. I have onlytested the extended receive which gives you from 118-174.995 and 320-479.995.Open the case by removing all the screws on the top, bottom and left/right sides and separating the top and bottom covers fromthe chassis.Next remove the plastic front panel that covers the logic circuit board by removing the two top and two bottom screws thatattach it to the chassis.Next remove the front panel logic board by taking out the four front screws that attach it to the chassis.Position the logic board so that the side normally near the chassis is on top and a round flat battery attached via leads is visiblewith the connector near the bottom and the cut out at the bottom right.Below the battery on the lower right there are a number of diodes, most likely surfaced mounted. Look just to the left of thediodes, there will be a very small surface mount jumper at the bottom (-#WW#- on diagram below). There is no silk screen onthe board to identify it (on mine at least) but the part itself may have a zero printed on it for zero ohms. Removing this jumperwill give you extended receive capability.Diagram (very bad but hopefully you get the idea)R O U N DB A T T E R Y! ! ! ! !! # # # # -#D#-D D D D -#D#- -#D## # # # ! -#D#- -#D#--#WW#- ! ! ! ! -#D#- -***-This modification is read 932 times.top of page19-07-1998(IC-281) Extended Transmit for IC-281By removing one of the diodes in the area mentioned above extended transmit is purported to be possible. I have not verifiedthis since I don't need this capability but it is supposed to significantly extend the transmit capability in the VHF band.To enable extended transmit remove the diode that is most near the right hand bottom part of the board as indicated in thediagram above with -***-.Reassemble and reset CPU per instruction manual.Note:When you reset the CPU you loose all memory and have too re-program all.This modification is read 899 times.top of page19-07-1998(IC-2AT) Coverage IC-2AT 140-150 MHzIf you have studied the schematic diagram for this radio, you will notice that pins 15 and 16 are not indicated on theprogrammable divider chip IC1 (TC9122).By simply connecting pin 15 thru a switch to pin 1, you will be able to move the radio up in frequency by 10 MHZ.Some of these radios were sold without covering 140-150 MHZ.The modification for this extended coverage is described below:1. Open up the radio and locate the FLEXIBLE BOARD, this connects the thumbwheel switches to the MAIN BOARD.2. At the MAIN BOARD end of the FLEXIBLE BOARD, add a jumper at location C4. There should already be a jumper at locationC2.