Modifications for the ICOM - RogerK

19-07-1998(IC-275) Improve the stability of the center meterReplace C81 on the main board (currently 120pf 50 CH type capacitor) with a 120 pf 50V SH temperature coefficient capacitor(ICOM P/N 918-05960).This modification is read 685 times.top of page19-07-1998(IC-275) Noise coming from speaker during transmit with audio turned upReplace R125 (currently a 47K resistor) on the main board with a 10K resistor.This modification is read 674 times.top of page19-07-1998(IC-275) Eliminate possible spurious emission when thermal switch has turned on during TXMay 1, 1989Procedure1. Remove top and bottom covers.2. Remove PA section from radio.3. Remove shield from power amplifier.4. Replace R7 (originally 10K 1/4W) resistor with a 1K 1/4 watt resistor (ICOM part number 915-01165).5. Replace R8 (originally 10K 1/4W) resistor with a 1K 1/4 watt resistor (ICOM part number 915-01165).6. Replace the shield on the PA section.7. Replace the PA section in the radio.8. Replace the top and bottom covers.This modification is read 671 times.top of page27-10-1998(IC-275) Frequency range & CTCSS tonesThe IC-275 have capability to cover 138 - 174 MHz and the IC-475 has capability to cover 430 - 450 MHz. Because of hardwarerestrictions they might not be fully up to specifications in all of the band, but an extended range can be interesting for e.g. usewith a transverter. It seems that the IC-275 has a parallel wide band preamp, that can be switch via the WBT pin on RF-YGRPCB.In the European versions the transceivers are wired for 1750 Hz repeater call, and they have no CTCSS capability. Thetransceivers have a built-in CTCSS encoder, so these functions can be restored.Both of these version dependent functions can be set by the diode matrix: D20 - D24 in the logic unit. I do not know the exactmapping, but a lot can be derived from studying the different frequency ranges and the diode matrix coding table found on theschematic diagram.This modification is read 742 times.top of page