Modifications for the ICOM - RogerK

OPTION 1CHANGES ARE IMPLEMENTED EXACTLY AS DISCUSSED IN THE PRECEDING TEXT:A. Remove the top and bottom covers. Place the receiver (top side facing up) on a stack of magazines or large books at least2" thick. Only the metal chassis should rest on the stack, not the front panel.B. You will see two flathead screws on either side of the receiver which hold the front chassis assembly to the main chassis.Remove only the top screw on each side and loosen the lower ones slightly. Using the lower two screws as a hinge,carefully fold the front assembly down so that the face of the radio rests on the desk. (A soft cloth may be used to preventscratches.)C. Right beneath the back of the S-meter, you will see a PC board to which the wide and narrow filter switches connect. Locatethe 12 solder points in a straight row associated with the two switches. There is a slight gap between the switches whichcontains two additional solder points just above and below those in the line. (The board layout diagram supplied with theservice manual is quite helpful in locating the appropriate solder points.) You need to create solder bridges across theoutermost set of normally open/normally closed switch contacts for each of the two switches. The appropriate pins areshown below:wide switch narrow switch bottom of radio^. | XX=solder. .XX. . . . . . . .XX. . | bridge.D. Inspect your work. Carefully return the front assembly to its proper position and secure the four flathead mounting screws.Re-install the bottom cover.E. Turn ON the filter switch (S1) on the main PC board. This switch will already be on if an optional CW narrow filter has beeninstalled. S1 is a small slide switch not far from the center of the board.F. You may wish to verify that everything is working OK so far. If so, be sure that all tools, etc. are out of harm's way andreconnect power, antenna and an external speaker to the receiver. The bandwidth switches should work the same asbefore, except that (1) there will be no receive with both switches pushed in and (2) there will be no receive with the"narrow" switch pushed in unless an optional CW filter is installed. Disconnect power again once the tests are complete.G. Locate D37 on the main PC board right next to IC3 near the center of the board. Cut the top (cathode) lead of the diode,leaving enough wire on both sides of the cut to make connections to. Bend the wire lead on the diode up. Solder a jumperwire from the cathode lead of D37 to the cathode (top) lead of D39 (located on the opposite side of IC3).H. PERFORM THIS STEP ONLY IF YOU WISH TO MAKE THE "IF-SHIFT" MODIFICATION FOR THE SSB/CW/RTTY "BOTHSWITCHES OUT" POSITION, AS DISCUSSED IN THE PREVIOUS TEXT. IF YOU ONLY WANT THE EXTRA AM BANDWIDTH,SKIP TO STEP "I." Cut the top (cathode) lead of D44, leaving enough wire on both sides of the cut to make connections to.Bend the wire lead on the diode up and solder a jumper wire from it to the top (cathode) lead of D42 (located near filterswitch S1).I. A switching diode must be connected from pin 4 of IC3 to the top (cathode) lead of D36 (located right next to D37). Asecond diode must be connected from pin 4 of IC3 to the lead sticking out of the PC board which was clipped from D44. IfD44 was not clipped in step H, the diode just connects to top (cathode) lead of D44. To make the IC3 connection, tin bothpin 4 and the lead which will connect to it; then place the two in contact with each other and heat up the connection.I performed this step by first soldering the anode of one of the switching diodes to the anode of the second; right where thelead enters its base. I then cut the anode lead of the first diode to a fairly short length and soldered it to pin 4 so that thetwo diodes were held in a vertical position just a tad above the IC. I then clipped the two cathode leads very short and raninsulated jumper wires from one cathode to D36 and from the other cathode to the D44 clipped lead coming out of the PCboard. However you decide to do it, make sure the IC3 connection does not short out any other pins and make sure theswitching diode leads cannot come in contact with any other components.J. Inspect your work and verify all steps were done properly. Make sure all tools are out of harm's way and test themodification. If everything works OK, reassemble the receiver. Note that with this modification, the narrow button must bein the "out" position for the FM unit (if installed) to function properly.OPTION 2CHANGES ARE IMPLEMENTED EXACTLY AS DISCUSSED IN THE PRECEDING TEXT EXCEPT THE "NARROW" FILTERSWITCH IS USED INSTEAD OF THE "BOTH SWITCHES IN" CONFIGURATION TO ACCESS THE ADDITIONALBANDWIDTH. THIS OPTION MAY ONLY BE USED IF NO CW NARROW FILTER HAS BEEN INSTALLED IN THERECEIVER.