Modifications for the ICOM - RogerK

The trimpot leads will need to bent in order to fit, and the wiper will need a small length of wire added to it so that it makesthe distance to the hole in the PCB.Picture 3 - 10k trimpot fitted to where J20 used to be.This allows you to retain the "Data Level" control, albeit a trimpot inside the radio.17. The Main Unit PCB can now be re-fitted and screwed back down.Don't forget to reconnect the coaxial lead to J2 and the internal speaker feed to J17.This male connector is now used for connecting +8 volts, ground, and the PBTV line to the pot.18. So, on the "old J20" male connector we now need, matching the leads from the pot on the female connector;Red (wiper)Braid (CW end)The blue wire (PBTV line)GroundWhite (CCW end)+8 voltsThere are many spots around the PCB to obtain +8 volts and ground from, but the easiest spot to access is IC15, a 4066.This is located just to the rear of the (big) 9.0105MHz crystal - see photo. Connect to Pin 14 for +8 volts and pin 7 forground.19. To prevent shorts, tape over where you have soldered the wires to the (J20) connector.Making use of these connectors, rather than cutting them off and soldering the wires directly to each other, improvesaccess and serviceability to the Main Unit PCB, should that be required at a later date.AlignmentIt's not absolutely necessary to tweak anything but if you are fastidious about alignment and have an accurate Digital FrequencyMeter, hook it up to the "test point" at R209, a 100R resistor. Those of you with an IC-575 Service Manual can refer to page 2-4for PBT alignment.Here is the procedure anyway;20-1 With the radio receiving in the AM mode and PBT set to full CCW, adjust L17 for a frequency of 9.46830 MHz.20-2 Centre the PBT control. Adjust R90 for 9.46500 MHz.20-3 With the PBT still centred, change to USB mode and adjust R93 for 9.46650 MHz.20-4 Change to FM mode. Adjust R95 for 9.46650 MHz. (Adjusting the PBT whilst in FM mode should make no difference tothis).21) Before you screw the bottom cover of the radio back on you'd better adjust the "Data Level" trimpot to suit yourrequirements.Make sure you have reconnected the internal speaker feed to J17, the coaxial lead to J2, and the connector to J10.22) Refit the bottom cover and screw in the nine screws.23) Reconnect power and antenna feeds and confirm normal operation.